ArtUSA University

ABC’s of Noise Control – ArtUSA Glossary of Noise and Sound Control Terms

Absorption

A property of materials that allows a reduction in the amount of sound energy reflected. The introduction of an absorbent into the surfaces of a room will reduce the sound pressure level in that room by not reflecting all of the sound energy striking the room’s surfaces. The effect of absorption merely reduces the resultant sound level in the room produced by energy that has already entered the room.

Absorption Coefficient

A measure of the sound-absorbing ability of a surface. It is defined as the fraction of incident sound energy absorbed or otherwise not reflected by a surface. Unless otherwise specified, a diffuse sound field is assumed. The values at the sound-absorption coefficient usually range from about 0.01 for marble slate to almost 1.0 for long absorbing wedges often used in anechoic rooms.

Acoustics

(1) The science of sound, including the generation, transmission, and effects of sound waves, both audible and inaudible. (2) The physical qualities of a room or other enclosure (such as size, shape, amount of noise) that determine the audibility and perception of speech and music within the room.

Acoustical Engineering

Acoustical engineering is the branch of engineering dealing with sound and vibration. It is closely related to acoustics, the science of sound and vibration. Acoustical engineers are typically concerned with:

how to reduce unwanted sounds

how to make useful sounds

using sound as an indication of some other physical property

The art of reducing unwanted sounds is called noise control. Noise control engineers work with engineers in most industries to ensure that their products and processes are quiet.

The art of producing useful sounds includes the use of ultrasound for medical diagnosis, sonar, and sound reproduction.

A separate and related discipline, audio engineering, is the art of recording and reproducing speech and music for human use.

Acoustic Trauma

Damage to the hearing mechanism caused by a sudden burst of intense noise, or by a blast. The term usually implies a single traumatic event.

Airborne Sound

Sound that reaches the point of interest by propagation through air.

Ambient Noise

The total of all noise in the environment, other than the noise from the source of interest. This term is used interchangeably with background noise.

Anechoic Room

A room in which the boundaries absorb nearly all the incident sound, thereby, effectively creating free field conditions.

A.N.S.I.

The American National Standards Institute.

Articulation Index (AI)

A numerically calculated measure of the intelligibility of transmitted or processed speech. It takes into account the limitations of the transmission path and the background noise. The articulation index can range in magnitude between 0 and 1.0 . If the AI is less than 0.1, speech intelligibility is generally low. If it is above 0.6, speech intelligibility is generally high.

Attenuation

The reduction of sound intensity by various means (e.g., air, humidity, porous materials…).

Audio Frequency

The frequency of oscillation of an audible sound wave. Any frequency between 20 and 20,000 Hz.

Audiogram

A graph showing individual hearing acuity as a function of frequency.

Audiometer

An instrument for measuring individual hearing acuity.

A-Weighted Sound Level

A measure of sound pressure level designed to reflect the acuity of the human ear, which does not respond equally to all frequencies. The ear is less efficient at low and high frequencies than at medium or speech-range frequencies. Therefore, to describe a sound containing a wide range of frequencies in a manner representative of the ear’s response, it is necessary to reduce the effects of the low and high frequencies with respect to the medium frequencies. The resultant sound level is said to be A-weighted, and the units are dBA. The A-weighted sound level is also called the noise level. Sound level meters have an A-weighting network for measuring A-weighted sound level.

The A-weighted sound level LA is widely used to state acoustical design goals as a single number, but its usefulness is limited because it gives no information on spectrum content. The rating is expressed as a number followed by dBA, for example 36 dBA. A-weighted sound levels correlate well with human judgments of relative loudness, but give no information on spectral balance. Thus, they do not necessarily correlate well with the annoyance caused by the noise. Many different-sounding spectra can have the same numeric rating, but have quite different subjective qualities. A-weighted comparisons are best used with sounds that sound alike but differ in level. They should not be used to compare sounds with distinctly different spectral characteristics; that is, two sounds at the same sound level but with different spectral content are likely to be judged differently by the listener in terms of acceptability as a background sound. One of the sounds might be completely acceptable, while the other could be objectionable because its spectrum shape was rumbly, hissy, or tonal in character. A-weighted sound levels are use extensively in outdoor environmental noise standards.

Background Noise

The total of all noise in a system or situation, independent of the presence of the desired signal. In acoustical measurements, strictly speaking, the term “background noise” means electrical noise in the measurement system. However, in popular usage the term “background noise” is often used to mean the noise in the environment, other than the noise from the source of interest.

Band

Any segment of the frequency spectrum.

Band Pass Filter

A wave filter that has a single transmission band extending from a lower cutoff frequency greater than zero to a finite upper cutoff frequency.

Broadband Noise

Noise with components over a wide range of frequencies.

Broadcasting Noise Control Products

Creating acoustically ideal rooms is challenging, particularly if existing spaces must be adapted. By absorbing, blocking and containing the areas of concern— flutter echo, near field reflection, room resonances, standing waves, exterior sounds—ArtUSA Industries professional solutions effectively and affordably solve acoustic control issues. The right sound is critical. That’s why ArtUSA Industries is dedicated to meeting the need of sound engineers and producers in every corner of the globe. We solve noise problems in television, radio and film studios as well as religious recording and audio test facilities such as ABC, DISNEY, CNN, TBS and many others. ArtUSA Industries affordable, fire-resistant and easy-to-install acoustical wall panels, ceiling tiles and barrier materials are designed to help deliver the right sound. Art-Barrier products help you isolate studios and listening rooms from outside sounds. Art-Tile Ceilings are perfect for control rooms, offices and lobbies, and offer aesthetics as well as one of the industry’s highest noise reduction ratings. Art-Tile metal ceiling tiles create a sleek, modern or high-tech look at an affordable price in offices, lobbies and conference rooms— without sacrificing acoustic control. Art-Fab wall panels are gaining popularity for their combination of sleek design and outstanding acoustic control in all frequencies with components over a wide range of frequencies.

Calibrator (Acoustical)

A device which produces a known sound pressure on the microphone of a sound level measurement system, and is used to adjust the system to Standard specifications.

Church Noise Control Products

In churches, synagogues and worship centers large or small, words and music can sound incomprehensible to the congregation if sound is not properly controlled. Poor sound quality is common in churches because of an abundance of hard surface materials. Brick, marble, stone, tile, glass, wood and sheetrock are all acoustically reflective. Sound waves bounce back and forth between parallel surfaces, creating a confusion of noise until they finally decay. Even the most strategically-placed speakers and microphones will not compensate for poor acoustics. Every room needs some absorptive materials and some reflective materials to get the right acoustic mix for the room’s intended purpose. The challenge is to find that balance. Art-Fab and Art-Sorb panels from ArtUSA Noise Control Products Inc. are designed to absorb airborne sound energy and reduce a room’s overall noise, reverberation and standing waves—creating interiors that reduce the din without sacrificing the divine. The right balance between absorption and reflection using strategically placed acoustic wall panels and baffles, create a more enjoyable worship and listening experience. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help the message and experience Lightweight and easy to install wall and ceiling treatments reduce reverberation and absorb sound from all directions. Traditional and or innovative solutions noise control and sound quality issues are our mission.

Cochlea

A spirally coiled organ located within the inner ear which contains the receptor organs essential to hear

Community and Environmental Noise

When neighbor businesses or residents feel there is excessive noise from industrial premises they complain. Environmental protection has become increasingly important. In addition to air and water quality, noise generation is a key environmental concern. Whether building a new facility or reducing noise at an existing site assuring that industrial noise will not be an issue is important. Analysis and design as well as the the supply and installation of the acoustical solutions should be an integral part of planning. In existing facilities investigating and dealing with a problem at an early stage promotes the companys responsible image and can save money in the long run. Combat community and environmental noise with our innovative products.

Comparable Table of Sound Level

A scale of compared sounds

Measurement of the distance to the specific sound source is important
Examples	dBA
Jet aircraft at 150 ft away	140
Threshold of pain	130
Threshold of discomfort	120
Chainsaw at 3 ft	110
Disco 3 ft from speaker	100
Diesel truck at 30 ft away	90
Curbside of a busy road at 15 ft away	80
Vacuum cleaner at 3 ft	70
Conversation at 3 ft	60
Average ambient noise in the home	55
Very quiet library	45
Very quiet country bedroom at night	35
Background in TV studio	25
Rustling of leaves	15
Threshold of human hearing	0

Cutoff Frequencies

The frequencies that mark the ends of a band, or the points at Which the characteristics of a filter change from pass to no-pass.

Cycle

The complete sequence of values of a periodic quantity that occurs during one period.

Cycles per Second

A measure of frequency numerically equivalent to hertz.

Cylindrical Wave

A wave in which the surfaces of constant phase are coaxial cylinders. A line of closely-spaced sound sources radiating into an open space produces a free sound field of cylindrical waves.

Damping

The dissipation of energy with time or distance. The term is generally applied to the attenuation of sound in a structure owing to the internal sound-dissipative properties of the structure or to the addition of sound-dissipative materials.

dBA

Unit of sound level. The weighted sound pressure level by the use of the A metering characteristic and weighting specified in ANSI Specifications for Sound Level Meter, S1.4-1983. dBA is used as a measure of human response to sound.

Decibel

A unit of sound pressure level, abbreviated dB.
– The Decibel is used to calculate changes in sound and power pressure levels.
– The Decibel is equal to ten times the logarithm to base 10 of the ratio of two quantities:
L = 10 log (E1 / E2)
where
E1 and E2 are the two quantities.

Diffraction

A modification which sound waves undergo in passing by the edges of solid bodies.

Directivity Index

In a given direction from a sound source, the difference in decibels between (a) the sound pressure level produced by the source in that direction, and (b) the space-average sound pressure level of that source, measured at the same distance.

Doppler Effect (Doppler Shift)

The apparent upward shift in frequency of a sound as a noise source approaches the listener or the apparent downward shift when the noise source recedes. The classic example is the change in pitch of a railroad whistle as the locomotive approaches and passes by.

DOSIMETER –

A device worn by a worker for determining the worker’s accumulated noise exposure with regard to level and time according to a pre-determined integration formula.

Ear (Human)

What is this strange and wonderful thing we call hearing. Consider the auditory sense in comparison to vision. The threshold stimulus for vision is much less than for hearing. The dark-adapted eye needs only 0.5 attajoules (aJ) of energy falling on it to perceive light. The ear requires 100J of energy falling on the ear-drum to perceive a sound.

In the comparative dynamic ranges of seeing and hearing, however, we find a dramatically greater versatility in the ear .The dynamic range of perception is the difference, in decibels, between the Just noticeable threshold and the level of stimulus that damages the sensory organ. The dynamic range of seeing is about 9OdB an extraordinary dynamic range by any standard. The dynamic range of hearing in a young person of moderate musical tastes is 140dB, 5OdB more than for seeing; it is the visual dynamic range multiplied by 100,000. The frequency response of perception is the range of frequencies over which the sensory organ operates, usually figured in octaves. The frequency range of visible light runs from the infrared to the ultraviolet, from 460 terahertz (THz) to 750THz, about 0.7 octaves. The frequency response of audible sounds, by contrast, runs from 20 Hz to 20kHz, 10 octaves. High-order brain processing is connected to the eyes and the ears, but I argue that more cerebral processing is employed for hearing than for sight.

Consider, analogously, the simplicity of technical equipment required to analyze stereoscopic photographs and the sophisticated technical equipment needed to analyze sonar recordings. Consider that our ears are always active and that the sounds are always being evaluated, even while we sleep. When the baby cries or a thief switches on the car engine, we awaken. They are truly miracles, these things on the sides of our heads. Let’s consider their anatomy and the way they work.

The outer ear

The part of the hearing mechanism presented to the outside world is a cartilaginous flap of skin called the pinna, or auricle. It has an asymmetrical shape useful in localizing the source of sound around the head. Though we are not accustomed to looking at them closely, pinnas are just as individual as faces: No two are perfectly alike. Running through the temporal bone of the skull is the ear canal, also called the auditory canal, the auditory meatus or, plainly enough, the earhole. Terminating the Inside end of the ear canal is the eardrum or tympanum, also sometimes called the tympanic membrane. This Is a circular plate of fibers, both radial and circumferential, attached to the ear canal all the way around its own circumference. It’s quite easy to rupture the eardrum, and It usually heals quickly, but each rupture can stiffen the eardrum, and enough ruptures can affect the hearing. The outer ear is inspected with an otoscope, an instrument with an internal light and a lens.

The middle ear

An open cavity within the temporal bone of the skull, between lcm cubed and 2cm cubed in volume, contains the ossilcles, which are three very small bones used to transmit the vibrations of the eardrum. The outer bone is the malleus, or hammer. Its lower end is attached to the inside of the eardrum. Also connected to it is the tensor tympanum, a very small muscle that applies tension to the eardrum through the malleus. The upper end of the malleus is connected to the incus, or anvil, the second small bone of the middle ear. The malleo-incudal joint Is held together with semi-flexible tendons, and there is an unexpected phenomenon here. When the eardrum flexes Inward, it pushes the malleus, which directly pushes the Incus. When the eardrum flexes outward, however, It pulls the malleus with it, and the upper tip of the malleus actually separates from the end of the Incus. The tendons at the Joint stretch with each flexure. Therefore, from the middle ear on, the human hearing mechanism Is asymmetrical. It responds instantly to compression waves pushing in the eardrum, but it responds with an elastic hysteresis to rarefaction waves that draw out the eardrum. A lever motion of the malleus sets the incus into rocking motion. The inner end of the incus is attached to the stapes, or stirrup, the last of these tiny bones in the middle ear. The stapes moves linearly, driven at its smaller end by the rocking of the Incus. The larger end, the foot, of the stapes completely covers an opening to the innermost part of the ear .This opening is called the oval window. A muscle called the stapedius can pull down the tip of the stapes, away from contact with the incus. This action is called the acoustic reflex, and It is stimulated by over-excursion of the ossicles, usually the result of a very loud, impulsive sound. It provides about 2OdB of vibration attenuation and requires about 175ms to take effect. The result is called a temporary loudness shift (TLS). This hollow (but busy with activity) chamber, the middle ear, Is connected to the rear of the throat by means of the Eustachian tube. This airway permits air pressures to be equalized between the two sides of the eardrum, but it can become clogged and provide a route of infection to the middle ear. The Eustachian tube is named after its discoverer, Bartolommeo Eustachio (1520~1574), an Italian physician and anatomist who worked in the days of the resurrection men, when human bodies could not legally be obtained for study.

The inner ear

The foot of the stapes covers the oval window and moves back and forth with the vibrations of the incus (and, through the incus, with the vibrations of the malleus and, through the malleus, with The cochlea contains the scala vestibuli, the scala tympani and the cochlear duct, where vibration is converted into nerve impulse the vibrations of the eardrum). The oval window is a flexible, membrane covered interruption in a bony wall between the middle ear and the inner ear. All of the structures and organs of the inner ear are suspended within the membranous labyrinth. This is a series of communicating sacs and ducts, protected from the bony osseous labyrinth (the chambers within the temporal bone) by a form of spinal fluid called the perilymph. The major organs of the Inner ear are the cochlea and the semicircular canals. These are fined with a gelatinous, serous fluid, similar to the fluid inside cells, called endolymph. Once a vibration is transmitted by the stapes through the oval window into the Inner ear, it becomes a fluid flow. When the stapes compresses the fluid within the oval window, the fluid needs a pressure release. This is provided by the round window, or fenestra rotunda.The round window, like the oval window, is a membrane covered opening in the wall between the middle and inner ear. When the stapes pushes the fluid in, the round window bulges back out into the middle ear. Immediately within the inner ear is the vestibule, a chamber into which vibrations from the cochlea and the semicircular canals emerge. At the top of the vestibule, three curved tubes are arranged at right angles to each other so that each tube curves through one perpendicular plane of three-dimensional space. The upper tube is called the superior; it curves up. The rear tube is called the posterior; it curves horizontally. The tube at the side curves around the side and Is called the lateral. These three tubes, called the semicircular canals, are used to sense the orientation of the head. For this purpose, they are filled with otolith, or ear sand. This colorfully named stuff consists of crystals of calcium carbonate, which move across sensing hair cells in the semicircular canals. This works analogously to a carpenter’s bubble level, except that, instead of a bubble finding the highest point of a curved tube, the ear sands drift around the lowest parts of curved tubes. They contribute to the sense of equilibrium and balance.

The cochlea

Now we come to the cochlea, the mystery at the center of human hearing. Its interior was first described in 1851 by Alfonso Corti (1822-1876). Great advances in the understanding of cochlear mechanics and electro-physiology were made throughout his life by George Von Bekesy (1899-1972), who started as an engineer with the Hungarian telephone company but found that his auditory researches gradually took over his career. In 1961, his research in ear anatomy won him the only Nobel prize ever given In any area of acoustics. The cochlea is a helically coiled tube, which spirals about 2 times around a bony structure called the modiolus. It has three chambers running along its length. A very thin shelf of bone, called (appropriately) the bony shelf, or osseous spiral lamina, projects Into the cochlea from the modiolus, dividing it almost in half along Its length. At the tip of the bony shelf, two membranes spread apart, rather like the arms of the letter Y. One of these is quite sturdy and is called the basilar membrane; the other is much thinner and more delicate and is called Reissner’s membrane, after Ernst Reissner (1824-1873). Between these membranes runs the cochlear duct. or scala media. Within the cochlear duct are the structures that convert vibrations of the fluid to nerve impulses. The channel running along the cochlea and Reissner’s membrane, and connected to the oval window, is the scala vestibuli. The other major channel along the cochlea, the scala tympani, starts at the round window and runs along the basilar membrane. These canals get smaller and smaller along the length,of the cochlea, and at the apex are connected by a small opening In the basilar membrane called the helicotrema. The scala vestibuli and the scala tympani are filled with perilymph, which can flow through the helicotrema to equalize the static fluid pressures. When the stapes pushes on the oval window, fluid pressures are actually transmitted all the way up the scala vestibuli. It is within the cochlear duct that the real action takes place. This canal is much smaller than the scala vestibuli or the scala tympani and is filled with endolymph, which is much thicker than perilymph, Running along the cochlear duct, and resting on the basilar membrane, is the organ of Corti. On one side, hair cells or cilia protrude Into the cochlear duct ; on the other side are the most peripheral nerve cells, called Corti’s ganglion, of the auditory nerve (or eighth cranial nerve). The hair cells In the organ of Corti actually terminate in a bundle of hairs, around 50 per cell. These are organized into a conical pattern, something like the stakes of a tepee. Electrically, the hair cells are capacitor plates. One end of the cell touches the perilymph on the other side of the basilar membrane; tile other end, with the tips of hairs, floats in the endolymph. Because the perilymph has a higher concentration of sodium ions and a lower concentration of potassium ions than does the endolymph (or, Indeed, the Interior of the hair cell), the resting hair cell has a potential of about -6OmVdc. When the bundle of hairs is deformed in one direction by waves In the cochlear fluids, its potential is changed to about -40mVdc; when deformed an equivalent amount in the other direction, it is changed to about -65mVdc. This is yet another asymmetry in the auditory pathway.These changes in the voltage of the hair cells affect the nerve cells Immediately below. It is important, however, to remember that the nerve cell Is not transmitting an analog current up to the brain. Nerve cells don’t transmit continuously nuctuating signals. Rather, they electrochemically transmit impulses, or spikes; this is called nerve cell firing. It is important to remember that the electrochemical behavior of the hair cells does not correspond precisely to the velocity or the displacement of the basilar membrane, which is why purely mechanical models of cochlear behavior yield so little useful Information about hearing. The auditory nerve brings impulses to the temporal lobes of the brain, that part of the brain immediately above the middle and inner ear. You will sometimes find It said that a pure tone agitates only one very small area of the basilar membrane. This theory goes on to say that the way the brain knows what frequencies are being heard is by identifying which hair cells are in motion. That was actually believed by otophysiologists at one time, about a century ago. It’s true there are resonance behaviors within the cochlea, and the resonance antinodes occur at about 0.2 octaves per millimeter. Still, virtually every sound agitates virtually every hair cell in the cochlea. Frequency discrimination is a rather higher-order brain function than anything going on in the inner ear .There are good theories about how it works, but the theories rely on psychological testing as much as study of ear mechanics or electrochemistry. The ear actually emits sound at frequencies the ear can hear properly. A damaged ear, with hair cell loss in the cochlea, will not emit sounds in the frequency ranges of hearing loss. This peculiar fact, disputed until recent years, suggests that active amplification, mechanical gain, occurs In the cochlea. The cochlear amplifier theory explains much about hearing that is otherwise inexplicable. There is no mechanism yet known by which the cochlea could amplify the vibrations transmitted to it.

Echo

A wave that has been reflected or otherwise returned with sufficient magnitude and delay, so as to be detected as a wave distinct from that directly transmitted.

Educational Noise Control

In classrooms, gymnasiums, indoor pools and other learning environments, poor speech intelligibility—the ability to understand what is being spoken—can adversely affect learning, achievement and enjoyment. The culprit is background noise and reverberation or echo. ArtUSA Noise Control Products, Inc. helps solve these issues in new and existing schools with cost- effective, long-lasting and easy to install enclosures, ceiling tiles, wall panels, baffles and other acoustical solutions. It is something educators know intuitively and research supports—high levels of background noise and reverberation or echo hinder learning. So, what’s the solution as class sizes continue to increase and budgets continue to shrink? ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help education and training sound better and positively influence learning. Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in indoor pools, gymnasiums, multipurpose rooms and other large interior spaces. Baffles are offered in a variety of standard and custom colors to complement or match school colors. Fabric-wrapped wall panel absorbs up to 85% of the sound directed toward it. They are available in hundreds of fabrics to complement or match school colors in classrooms, music rooms, offices and gymnasiums. Ceiling tiles with a backer board drop into a standard grid system and help block sound traveling from adjacent rooms. Tiles without a backer board can be adhered to any wall or ceiling surface making them ideal for rooms without a grid system or those with low ceiling heights.

Equivalent A-Weighted Sound Level (Leq)

The constant sound level that, in a given time period, would convey the same sound energy as the actual time-varying A-weighted sound level.

Free Field

Describes a sound source region in free space where the sound pressure level obeys the inverse-square law (the sound pressure level decreases 6 dB with each doubling of distance from the source). Also, in this region the sound particle velocity is in phase with the sound pressure. Closer to the source where these two conditions do not hold constitutes the near field region.

Filter

A device for separating components of a signal on the basis of their frequency. It allows components in one or more frequency bands to pass relatively unattenuated, and it attenuates components in other frequency bands.

Filters for Dust Collectors

Industrial air filters for dust collectors come in a distinct variety of formats. Certain dust collector filters technologies work best with certain applications. On this page, you can learn about HEPA air filters, electrostatic precipitators, pleated bag filters and cartridge filters.

Grain of Sand 80-2000 ?m Human Hair 30 – 200 ?m Settling Dust 10 – 100 ?m Inhalable Dust 8.0 – 12 ?m Respirable Dust 1.0 – 5.0 ?m Smoke Particle 0.01 – 1.0 ?m

Characteristics of Dust

On one end of the spectrum you have tiny suspended dust particles that can be filtered through an ambient air cleaner. This may be background haze you barely notice, yet causes serious respiratory conditions. Respirable dust is 1.0 – 5.0 microns in size and able to penetrate deep into the respiratory system, past the body’s cilia, mucous and natural defense mechanisms. Inhalable dust is bigger, around 10 microns in particle size, enters the body, but gets trapped by the bodies natural filtering mechanisms in the nose, throat and upper respiratory tract. For this atmospheric dust, you need filtration capable of capturing the smallest particles, either electrostatic precipitators (ESP), high quality media or HEPA filters. Most electrostatic air cleaners can use a HEPA after-filter. Anything with a post filter capable of capturing a good percentage of particles one micron or smaller will provide a noticeable difference. When looking at efficiency, you should always go by ASHRAE compliant filter media testing. Dust spot testing is often misleading. ASHRAE is the industry standard for describing filter efficiency based on different particle sizes.

HEPA Air Filters

Many people have heard of HEPA air filters. They have a reputation for being highly efficient. Here’s a little more information. High Efficiency Particle Arresting (HEPA) media was developed for protection against harmful particles emitted from radioactive substances. Any filter that is HEPA rated can capture 99.97% of particles 0.3 microns in diameter. This is according to ASHRAE testing. HEPA will stop any harmful respirable dust and most smoke particles. But this does not mean HEPA is your total solution. HEPA filters are usually a very fine weave. This means they constrict airflow and clog easily. If you are collecting tooling dust, wood cutting dust or anything heavier than light atmospheric dust, you will need more course prefilters to take out the bigger particles. Using a prefilter extends the life of a HEPA filter.

For dust collection, HEPA filters are best used as post filters on a multiple filter dust collection system or as a post filter or main filter in an ambient air cleaner used to remove light atmospheric dust from breathing zones.

Electrostatic Precipitators

Also called electronic air cleaners or ESP, electrostatic dust collectors also collect fine particles. As far as dust collection is concerned, ESP is pretty limited. Electrostatic cells do well with smoke and mist, but will load up very quickly with any amount of dust greater than light atmospheric. Like HEPA, most ESP is best used for ambient air cleaners. Although, extremely large electrostatic precipitators are used in smoke stacks to remove fly ash.

Pleated Bag Filters

For a long time, fabric bag filters have been the staple filtration mechanism for dust collectors. They are now being replaced by pleated media bag filters. The pleats greatly increase filter surface area. Layers of deep pockets made of woven fabric pack away heavy loads of dust. Pleated bag filters come in all shapes and sizes. When space is an issue, pleated bag filters the size of large box filters can often provide adequate dust collector filter media area. The picture to the right shows a pair of extended media filters. The surface area is extended by using deep pockets. In other cases, huge tube shaped pleated filter bags replace hanging, suspended or cage supported fabric bags from a baghouse. Often washable, efficient and capable of heavy loading, pleated filters, whether bag or cartridge, have become the current norm for industrial dust collection media.

Cartridge Filters

To date, cartridge filters are the most advanced form of media filtration. Also using extended surface area, manufacturers of replacement filters are constantly developing and improving media technology used in cartridges. Offering high efficiency across a broad range of particle sizes, cartridge filters can be used for just about any dust collection application. Cartridge filters are cylindrical shaped and open on one or both ends. Pleated filtration media wraps around the cylinder walls. When installed, one end is sealed off, leaving the open end as the exhaust. Air is sucked in through the filter sides and out the open end. Capable of reverse pulse cleaning, huge banks of cartridge filters can be used to continuously collect dust from a factory’s central dust collection system.

Firing Range Noise Noise Control Products

The sound produced by gunfire is deafening outdoors, but when the acoustical energy it produces is confined to a small indoor space as in a firing range, it gets even louder. The noise can reach levels as much as ten times greater than those experienced in outdoor ranges. Art-Sorb panels help eliminate this indoor “range effect” by absorbing sound waves that would otherwise build up to dangerous levels causing serious discomfort and even hearing damage. Additionally, they are relatively inexpensive and easy to install. Art-Sorb panels are ideal for indoor firing ranges because they are Class 1 fire-rated and have excellent sound absorption at 500 and 1000 Herz (Hz), the most common frequencies produced by gunfire. The sound absorption coefficient of most 2″ thick panels are between 0.73 and 1.05 at 500 and 1000 Hz. This means that the panels absorb between 73% and 100% of the acoustical energy at 500 Hz and 1000 Hz, depending upon the exact pattern. Panels are available in a variety of patterns and surface treatments to meet almost every firing range need. A surprisingly small amount of absorption goes a long way in most ranges. Typically, a range requires an amount of foam equal to the square footage of its ceiling. The foam is divided, however, between the ceiling and the walls for the most efficient sound absorption. This will normally reduce the amount of acoustical energy within the range by an amazing 85%. Measure the square footage of the ceiling as if you were covering it completely. Attach two-thirds of the panels ordered to the ceiling in one large block or in several bands starting directly above the firing positions and extending downrange to where the first signs of bullet damage begin to show on the ceiling. Attach the remaining one-third of foam to the walls, once again extending downrange from the firing stations to the first signs of bullet damage. Leave one to two feet clear above the floor to avoid damage to the foam panels by floor cleaning equipment. Also, avoid areas near switches and control panels to eliminate damage done by users and personnel. device for separating components of a signal on the basis of their frequency. It allows components in one or more frequency bands to pass relatively unattenuated, and it attenuates components in other frequency bands.

Free Sound Field (Free Field)

A sound field in which the effects of obstacles or boundaries on sound propagated in that field are negligible.

Frequency

The number of times per second that the sine wave of sound repeats itself, or that the sine wave of a vibrating object repeats itself. Now expressed in hertz(Hz), formerly in cycles per second (cps).

An introduction to the nature of sound with frequency, wavelength and octaves:

Sound energy is transmitted through air (or other particles) as a traveling pressure wave. In air the displacement wave amplitude may range from 10-7 mm to a few mm per second.

FREQUENCY
The frequency (cycles per second) of a sound is expressed in hertz (Hz).

f = 1/T (Hz)

The range for human hearing is from 20 to 20.000 Hz. By age 12-13.000 Hz are the limit for many people.

Wavelength
The wavelength of sound is the distance between analogous points of two successive waves.

l = c / f
where
c = speed of sound (m/s)
f = frequency (Hz)

Gym and Multipurpose Noise Control Products

From physical education classes, sporting events and school assemblies, to everyday cafeteria, overflow classroom space and general meeting areas, gymnasiums and multipurpose rooms are some of the most-used and most-populated areas on a school campus. With all the activities, sound levels can quickly build to boisterous levels. The large, open space, high ceilings, wood or tiled floors and painted concrete walls with school colors and themes give gyms and multipurpose rooms the flexibility to accommodate a wide range of student and community activities. However, these same traits also contribute to excessive reverberation and poor acoustics. Excessive echo, or reverberation, interferes with instruction between students and teachers, inhibits participation and enjoyment during events and reduces speech intelligibility of announcements. The hard, reflective surfaces commonly found in gyms and multipurpose rooms cause the sound waves to bounce around until they eventually decay or are absorbed. The right balance between absorption and reflection using strategically placed acoustic wall panels baffles and traps, creates a more functional and enjoyable space. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help gyms and multipurpose rooms sound better and positively influence events and learning. Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in indoor pools, gymnasiums, multipurpose rooms and other large interior spaces.

Hair Cell

Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.

Harmonic

A sinusoidal (pure-tone) component whose frequency is a whole-number multiple of the fundamental frequency of the wave. If a component has a frequency twice that of the fundamental it is called the second harmonic, etc…

Hearing

The subjective human response to sound.

Hearing Level

A measured threshold of hearing at a specified frequency, expressed in decibels relative to a specified standard of normal hearing. The deviation in decibels of an individual’s threshold from the zero reference of the audiometer.

Hearing Loss

A term denoting an impairment of auditory acuity. The amount of hearing impairment, in decibels, measured as a set of hearing threshold levels at specified frequencies. Types of hearing loss are:

1. Conductive Hearing Loss:
A loss originating in the conductive mechanism of the ear

2. Sensor-neural Hearing Loss:
A loss originating in the cochlea or the fibers of the
auditory nerve

3. Noise induced Hearing Loss:
A sensor-neural loss attributed to the effects of noise

Hearing Threshold Level (HTL)

Amount (in decibels) by which an individual’s threshold of audibility differs from a standard audiometric threshold

Hertz (Hz)

Unit of measurement of frequency, numerically equal to cycles per second

HVAC NOISE –

Mechanical and HVAC systems generate noise that can be transmitted into occupied spaces. Examples of acoustical problems include: 1) breakout noise from MER walls and doors, 2) vibration transmitted from blowers, 3) drumming of duct walls, 4) regenerated noise in ducts at elbows, dampers, and diffusers, and 5) excess fan noise propagated down the ductwork.
For noise problems that become apparent after a space is occupied, the first step is to establish a criterion for the affected room.
The second step is to meter then analyze it. The analysis reveals the severity of the noise problem and what frequencies are affected most.
The next step is to formulate options to reduce the noise based on the type of noise sources involved and their frequency spectra. These treatment options can be evaluated to select the most cost-effective solution.

Several background sound rating methods are used to rate indoor sound. They include the A-weighted sound pressure level dBA and noise criteria NC, the more recent room criteria RC and balanced noise criteria NCB, and the new RC Mark II. Each sound rating method was developed from data for specific applications; not all methods are equally suitable for rating the HVAC-related sound in the variety of applications encountered.
The degree of occupant satisfaction achieved with a given level of background sound is determined by many factors. For example, large conference rooms, auditoriums, and recording studios can tolerate only a low level of background sound. On the other hand, higher levels of background sound are acceptable and even desirable in certain situations, such as open-plan offices where a certain amount of speech and activity masking is essential. Therefore, the system sound control goal varies depending on the required use of the space.
To be unobtrusive, background sound should have the following properties:

• A balanced distribution of sound energy over a broad frequency range
• No audible or tonal characteristics such as whine, whistle, hum, or rumble
• No noticeable time varying levels from beats or other system induced aerodynamic instability
• No fluctuations in level such as throbbing or pulsing

Impact Insulation Class (IC)

A single-figure rating that compares the impact sound insulating capabilities of floor-ceiling assemblies to a reference contour.

Impact Sound

The sound produced by the collision of two solid objects. Typical sources are footsteps, dropped objects, etc., on an interior surface (wall, floor, or ceiling) of a building.

Impulsive Noise

• Either a single sound pressure peak (with either a rise time less than 200 milliseconds or total duration less than 200 milliseconds) or multiple sound pressure peaks (with either rise time less than 200 milliseconds or total duration less than 200 milliseconds) spaced at least by 200 millisecond pauses,

• A sharp sound pressure peak occurring in a short interval of time.

Industrial Noise Control Products

Excessive noise is one of the most common workplace hazards in industrial facilities. Prolonged exposure to noise in manufacturing, power generation, printing and other industries can result in compromised verbal communication, fatigue, lower productivity and work-related hearing loss. Manufacturing areas are not the only places where noise can be hazardous and counterproductive. Offices that share walls with factories or are subjected to outside noise from highways or airports face similar noise problems. In such environments, uncontrolled sound can interfere with the intended purpose of the space, resulting in hampered interpersonal communication, headaches and other problems. ArtUSA Noise Control Products Inc. offers many durable choices to easily and affordably create a healthier work environment. Noise control entails suppressing audible kinetic energy in two ways, and the most effective solutions may require a combination of the two: 1) Containing noise with enclosures and or barrier materials 2) Absorbing noise with panels, baffles and other acoustical absorber products. ArtUSA Noise Control Products Inc. offers flexible and rigid enclosure systems. Curtains are flexible and can either be used independently or as part of an enclosure system. Custom-configured enclosures can be made from a combination of products to produce an effective and economical method of noise reduction. Options include rooftop panels, grommets, view windows, sliding hinged and overhead doors, silencers, exhaust fans and more.

Industrial noise is usually considered mainly from the point of view of environmental health and safety, rather than nuisance, as sustained exposure can cause permanent hearing damage. Traditionally, workplace noise has been a hazard linked to heavy industries such as ship-building and associated only with noise induced hearing loss (NIHL). Modern thinking in occupational safety and health identifies noise as hazardous to worker safety and health in many places of employment and by a variety of means.

Noise can not only cause hearing impairment (at long-term exposures of over 85 decibels (dB)), but it also acts as a causal factor for stress and raises systolic blood pressure.

Additionally, it can be a causal factor in work accidents, both by masking hazards and warning signals, and by impeding concentration.

Noise also acts synergistically with other hazards to increase the risk of harm to workers. In particular, noise and dangerous substances (e.g. some solvents) that have some tendencies towards ototoxicity may give rise to rapid ear damage.

A-weighted measurements are commonly used to determine noise levels that can cause harm to the human ear, and special exposure meters are available that integrate noise over a period of time to give an Leq value (equivalent sound pressure level), defined by standards.

Industrial noise reduction

When two identical industrial noise sources are side by side producing a recorded noise at 100 dB(A) the reduction in noise from shutting off one of the noise sources is about 3 dBA resulting in 97 dBA.

When one doubles the distance from a noise source the recorded noise level is reduced by 6 dBA. This is also called the Rule of 6. This is based on the fact that the equation to calculate noise attenuation at a distance D₂, knowing the SPL at distance D₁ is given by , where D is the distance. If the distance is doubled, the equation simplifies to 20 * log(2) which equals 6.02 (or approx. 6)

Infrasonic

Sounds of a frequency lower than 20 hertz.

Intensity

The sound energy flow through a unit area in a unit time.

Inverse Square Law

A description of the acoustic wave behavior in which the mean-square pressure varies inversely with the square of the distance from the source. This behavior occurs in free field situations, where the sound pressure level decreases 6 dB with each doubling of distance from the source.

ISO

The International Organization for Standardization.

Level

The logarithm of the ratio of a quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be specified.

Logarithm

The exponent that indicates the power to which a number must be raised to produce a given number. For example, for the base 10 logarithm, used in acoustics, 2 is the logarithm of 100.

Loudness

The subjective judgment of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure (a tenfold increase in acoustical energy, or, 10 dB) to produce a doubling of loudness.

Loudness Level

Measured in phons it is numerically equal to the median sound pressure level (dB) of a free progressive 1000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud.

Masking

• The process by which the threshold of audibilty for a sound is raised by the presence of another (masking) sound.

• The amount by which the threshold of audibility of a sound is raised by the presence of another (masking) sound.

Masking Noise

A noise that is intense enough to render inaudible or unintelligible another sound that is also present.

Medium

A substance carrying a sound wave.

Near Field

The sound field very near to a source, where the sound pressure does not obey the inverse square law and the particle velocity is not in phase with the sound pressure.

Niosh

The National Institute for occupational Safety and Health.

Noise

• Unwanted sound.

• Any sound not occurring in the natural environment, such as sounds emanating from aircraft, highways, industrial, commercial and residential sources.

• An erratic, intermittent, or statistically random oscillation.

Noise Health Effects

Noise health effects, the collection of health consequences of elevated sound levels, constitute one of the most widespread public health threats in industrialized countries. Roadway noise is the main source of environmental noise exposure. Aerodynamic noise created at freeway speeds is particularly intense. Current conditions expose tens of millions of people to sound levels capable of causing hearing loss,^[1] but also are known to induce tinnitus, hypertension, vasoconstriction and other cardiovascular impacts.^[2] Vasoconstriction can also be contributory to erectile dysfunction.^[3]Beyond these effects, elevated noise levels create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors.^[4] The most important sources of sound levels that create the above effects are motor vehicle and aircraft noise, with industrial worker noise exposure also being notable. Secondary exposures may arise from loud audio media especially if practiced as a lifestyle such as prolonged portable audio player use.

The pinna (visible portion of the human ear) combined with the middle ear amplifies sound levels by a factor of 20 when sound reaches the inner ear. Approximately ten percent of the population in industrialized societies have significant hearing loss, and millions more are steadily progressing to that outcome. The major source of hearing loss is exposure to elevated sound levels. Once it was thought that only extremely high sound levels create hearing loss; however, more careful investigations showed that cumulative exposure to relatively moderate levels, such as 70 dB(A),^[5] can lead to the irreversible loss of hearing. Another myth of noise effects is the overstated role of presbycusis, or loss of hearing associated with aging. It has been demonstrated that the most important factor of hearing degradation is not aging alone, but rather the cumulative long-term exposure to environmental and occupational noise that create the harm.^[5] In the Rosenhall study, age cohort populations were tracked, with the result that noise-exposed persons had much greater hearing loss than their age cohorts who were relatively unexposed to noise. In fact, it has been shown that people in non-industrialized countries do not experience the same progressive hearing loss.^[6] Due to loud music and a generally noisy environment, young people in the United States have a rate of impaired hearing 2.5 times greater than their parents and grandparents.^[7]

The mechanism of hearing loss arises from trauma to stereocilia of the cochlea, the principal fluid filled structure of the inner ear. The pinna (visible portion of the ear) combined with the middle ear amplifies sound pressure levels by a factor of twenty, so that extremely high sound pressure levels arrive in the cochlea, even from moderate atmospheric sound stimuli. The cilial damage is known to be cumulative and can be irreversible.^[8] The most recent research indicates that high noise levels create elevated levels of reactive oxygen species in the inner ear,^[9] which interfere with the regenerative process for cochlear cilia repair. This research shows why high noise levels have differing effects over a given population, and lead to a possible preventative strategy of adequate antioxidant intake.

In 1972 the U.S. EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that are likely to lead to significant hearing loss.^[10] Given the significant increase in traffic, car ownership and air travel since that time, the worldwide implication for industrialized countries would place this exposed population in the hundreds of millions at a conservative estimate.

Cardiovascular disease and other health effects

Cardiovascular effects can result from excessive noise. Note especially the coronary arteries supplying the heart itself, which structures are sensitive to narrowing and hypertensive effects.

Important cardiovascular consequences follow from elevated sound levels, principally because the elevated adrenaline levels trigger a narrowing of the blood vessels (vasoconstriction). Sound levels, again of fairly typical roadway noise exposure, are known to constrict arterial blood flow and lead to elevated blood pressure; in this case, it appears that a certain fraction of the population is more susceptible to vasoconstriction. (Independently, high noise levels are known to produce medical stress reactions, another risk associated with cardiovascular disease.) Noise-induced medical stress is significant for two reasons. First, it often results from prolonged exposure for 8 to 16 hours per day, leading to elevated blood pressure for much of the day. Second, unlike emotional stress, it has a very clear effect on blood pressure, whereas this is not always true of emotional stress. These effects may be compounded by other environmental vasoconstrictors such as over-illumination or light pollution.

Other proven effects of high noise levels are increased frequency of headaches, fatigue, stomach ulcers and vertigo.^[11] The same U.S. EPA study establishes links between high noise levels and fetal development. This body of research suggests a correlation between low-birth-weight babies (using the World Health Organization definition of 5.5 pounds) and high sound levels, and also correlations in abnormally high rates of birth defects, where expectant mothers are exposed to elevated sound levels, such as typical airport environs. Specific birth abnormalities included harelip, cleft palate, and defects in the spine. According to Lester W. Sontag of The Fels Research Institute (as presented in the same EPA study): “There is ample evidence that environment has a role in shaping the physique, behavior and function of animals, including man, from conception and not merely from birth. The fetus is capable of perceiving sounds and responding to them by motor activity and cardiac rate change.” Noise exposure is deemed to be particularly pernicious when it occurs between 15 and 60 days after conception, when major internal organs and the central nervous system are formed. Later developmental effects occur as vasoconstriction in the mother reduces blood flow and hence oxygen and nutrition to the fetus. Low birth weights and noise were also associated with lower levels of certain hormones in the mother, these hormones being thought to affect fetal growth and to be a good indicator of protein production. The difference between the hormone levels of pregnant mothers in noisy versus quiet areas increased as birth approached.

Psychological effects

Earlier researchers often grouped the non-physiological impacts of noise as “annoyance”. As research unfolded, it became clear that there are a host of psychological and behavioral effects result from elevated sound levels, including: sleep disturbance, reading development in children, stress, mental health (including disengagement and increases in aggressive behavior). These effects are statistical but measurable changes in a population of individuals compared to a control group of persons in a quiet environment. Obviously, other negative environmental factors are likely to be present in high noise areas such as higher air pollution levels and possibly poverty-induced nutrition deficits; however, the overwhelming weight of dozens of independent studies identify noise pollution to be responsible for significant increases in the psychological effects studied above.

Measurements of noise annoyance typically rely on weighting filters, which consider sound frequencies annoying only to the degree that they are audible, on average, to a human ear at a particular decibel volume. Common methods include the older dBA weighting filter used widely in the U.S., which underestimates the impact of frequencies around 6000 Hz and at very low frequencies, and the newer ITU-R 468 noise weighting filter, which is used more widely. It is important to note that these filters do not necessarily reflect the occurrence of adverse health effects from noise, which may not depend on its audibility to the ear, nor do they take into account the propensity of low-frequency noises to penetrate into buildings or to carry over long distances.

Annoyance effects of noise vary greatly by demographics and by the perception of how useful the entity is that originates the noise. For example, aircraft mechanics who live near an airport are less likely to be complainants, since their livelihood is based upon airport operations. Annoyance is also influenced by whether the noise source is visible, whether it has pure tones or hammer effects and whether the recipient believes the noise can be controlled. In any case, the onset^[12] of noise complaints can be as low as 40 dB(A).^[13] However decibels don’t always tell the whole story: consider a maddening ever present faraway radio, vs. the occasional nearby dog bark. Whether the noise occurs at night is another critical variable for annoyance phenomena. Most commonly, concerted actions of the public appear at approximately 65dBA regarding roadway, aircraft or industrial noise in the environment. Closely associated with annoyance are sleep disturbance and speech interference phenomena. The threshold for sleep interference is 45 dB(A) or lower.^[14] The onset of speech interference is about 63dBA, or roughly the sound level of speech in a normal tone between two people separated by one meter.

When young children are exposed to speech interference levels of noise on a regular basis, there is a likelihood of developing speech or reading difficulties, because the auditory processing functions are compromised. In particular the writing learning impairment known as dysgraphia is commonly associated with environmental stressors in the classroom.

Effects of environmental noise upon aggression, mental health, anxiety, withdrawal and other psychological factors have been studied by numerous researchers. For example J.M. Field^[15] examines a variety of these outcomes and finds significant influence of moderate-level environmental noise upon human behavior and mood. There are also strong associative impacts when other stressors are present such as over-illumination and presence of certain drugs.

Noise Isolation Class (NIC)

A single number rating derived in a prescribed manner from the measured values of noise reduction between two areas or rooms. It provides an evaluation of the sound isolation between two enclosed spaces that are acoustically connected by one or more paths.

Noise Level

For airborne sound , unless specified to the contrary, it is the A-weighted sound level.

Noise Mitigation

Noise mitigation is a set of strategies to reduce unwanted environmental sound. The main topics of noise mitigation (alternatively known as noise abatement) are: transportation noise control, architectural design, and occupational noise control. Roadway noise and aircraft noise are the most pervasive sources of environmental noise worldwide, and remarkably little change has been effected in source control in these areas since invention of the original vehicles. The sole exception to have widespread potential impact is development of the hybrid vehicle.

A panoply of techniques have been developed to address interior sound levels, many of which are encouraged by local building codes; in the best case of project designs, planners are encouraged to work with design engineers to examine tradeoffs of roadway design and architectural design. These techniques include design of exterior walls, party walls and floor/ceiling assemblies; moreover, there are a host of specialized means for dampening reverberation from special purpose rooms such as auditoria, concert halls, dining areas and meeting rooms. Many of these techniques rely upon materials science applications of constructing sound baffles or using sound absorbing liners for interior spaces. Industrial noise control is really a subset of interior architectural control of noise, with emphasis upon specific methods of sound isolation from industrial machinery and for protection of workers at their task stations.

Roadway noise mitigation

This Hybrid vehicle can operate 15 to 25 decibels more quietly than conventional autos at speeds less than 60 km/h

Source control in roadway noise has provided little reduction in vehicle noise, except for the development of the hybrid vehicle; nevertheless, hybrid use will need to attain a market share of roughly fifty percent to have a major impact on noise source reduction on city streets. (Highway noise is little affected by automobile type, since those effects are aerodynamic and tyre noise related.) Other contributions to reduction of noise at the source are: improved tire tread designs for trucks in the 1970s, better shielding of diesel stacks in the 1980s, and local vehicle regulation of unmuffled vehicles.

The most fertile area for roadway noise mitigation is in urban planning decisions, roadway design, noise barrier design^[1], speed control, surface pavement selection and truck restrictions. Speed control is effective since the lowest sound emissions arise from vehicles moving smoothly at 30 to 60 kilometres per hour. Above that range sound emissions double with each five miles per hour of speed. At the lowest speeds, braking and (engine) acceleration noise dominates. Selection of surface pavement can make a difference of a factor of two in sound levels, for the speed regime above 30 kilometres per hour. Quieter pavements are porous with a negative surface texture and use medium to small aggregates; the loudest pavements have a transversely tined/grooved surface, and/or a positive surface texture and use larger aggregates. Obviously surface friction and roadway safety are important considerations as well for pavement decisions.

When designing new urban freeways or arterials, there are numerous design decisions regarding alignment and roadway geometrics^[2], Use of a computer model to predict future sound levels from line sources has become standard practice since the early 1970s. In this way exposure of sensitive receptors to elevated sound levels can be minimized. An analogous process exists for urban mass transit systems and other rail transportation decisions. Early examples of urban rail systems designed using this technology were: Boston MTA line expansions (1970s), San Francisco Bay Area Rapid Transit System expansion (1981), Houston light rail system (1982), Portland, Oregon Beaverton light rail line (1983).

Noise barriers can be applicable for existing or planned surface transportation projects. They are probably the single most effective weapon in retrofitting an existing roadway, and commonly can reduce adjacent land use sound levels by ten decibels. A computer model is required to design the barrier since terrain, micro meteorology and other locale specific factors make the endeavor a very complex undertaking. For example, a roadway in cut or strong prevailing winds can produce a setting where atmospheric sound propagation is unfavorable to any noise barrier.

Aircraft noise abatement

A British Airways Airbus A321, on landing approach to London Heathrow Airport, showing proximity to homes.

As in the case of roadway noise, surprisingly little progress has been made in source quieting of aircraft noise, other than elimination of gratuitously loud engine designs from the 1960s and earlier. Because of its velocity and volume, jet turbine engine exhaust defies any simple means of quieting. The most promising forms of aircraft noise abatement is through land planning, flight operations restrictions and residential soundproofing. Flight restrictions can take the form of preferred runway use; departure flight path and slope; and time of day restrictions. These tactics are sometimes controversial since they can impact aircraft safety, flying convenience and airline economics.

In 1979 the U.S. Congress authorized^[3] the FAA to devise technology and programs to attempt to insulate homes near airports. While this obviously does not aid the exterior environment, the program has been effective for residential and school interiors. Some of the first airports at which the technology was applied were San Francisco International Airport^[4], Seattle-Tacoma International Airport, John Wayne International Airport and San Jose International Airport^[5] in California. The underlying technology is a computer model which simulates the propagation of aircraft noise and its penetration into buildings. Variations in aircraft types, flight patterns and local meteorology can be analyzed along with benefits of alternative building retrofit strategies such as roof upgrading, window glazing improvement, fireplace baffling, caulking construction seams and other measures. The computer model allows cost effectiveness evaluations of a host of alternative strategies.

In year 1998 the flight paths in all of Scandinavia were changed as the new Oslo-Gardermoen Airport was opened. These new paths were straighter, consuming less fuel, and disturbing fewer people. However heavy protests came from people who weren’t disturbed before, and they took legal action etc (NIMBY effect).

Architectural solutions

Choices of stud construction, insulation and isolation of plumbing assemblies can reduce interior noise

Beyond the interior acoustics cited above under aircraft noise, there has been a steady trend to design quieter buildings with regard to sources within and without the structure itself. In the case of construction of new (or remodeled) apartments, condominiums, hospitals and hotels many states and cities have stringent building codes with requirements of acoustical analysis, in order to protect building occupants. With regard to exterior noise, the codes usually require measurement of the exterior acoustic environment in order to determine the performance standard required for exterior building skin design. The architect can work with the acoustical scientist to arrive at the best cost effective means of creating a quiet interior (normally 45 dBA). The most important elements of design of the building skin are usually: glazing (glass thickness, double pane design etc.), roof material, caulking standards,chimney baffles, exterior door design, mail slots, attic ventilation ports and mounting of through the wall air conditioners.

Regarding sound generated inside the building, there are two principal types of transmission. Firstly, airborne sound travels through walls or floor/ceiling assemblies and can emanate from either human activities in adjacent living spaces or from mechanical noise within the building systems. Human activities might include voice, amplified sound systems or animal noise. Mechanical systems are elevator systems, boilers, refrigeration or air conditioning systems, generators and trash compactors. Since many of these sounds are inherently loud, the principal design element is to require the wall or ceiling assembly to meet certain performance standards^[6] (typically Sound transmission class of 50), which allows considerable attenuation of the sound level reaching occupants.

The second type of interior sound is called Impact Insulation Class (IIC) transmission. This effect arises not from airborne transmission, but rather from transmission of sound through the building itself. The most common perception of IIC noise is from footfall of occupants in living spaces above. This type of noise is more difficult to abate, but consideration must be given to isolating the floor assembly above or hanging the lower ceiling on resilient channel.

Both of the above transmission effects may emanate either from building occupants or from building mechanical systems such as elevators, plumbing systems or heating, ventilating and air conditioning units. In some cases it is merely necessary to specify the best available quieting technology in selecting such building hardware. In other cases shock mounting of systems to control vibration may be in order. In the case of plumbing systems there are specific protocols developed, especially for water supply lines, to create isolation clamping of pipes within building walls. In the case of central air systems, it is important to baffle any ducts that could transmit sound between different building areas.

Designing special purpose rooms has more exotic challenges, since these rooms may have requirements for unusual features such as concertperformance, sound studio recording, lecture halls. In these cases reverberation and reflection must be analyzed in order to not only quiet the rooms but prevent echo effects from occurring. In these situations special sound baffles and sound absorptive lining materials may be specified to dampen unwanted effects..

Industrial noise mitigation

This situation classically is thought to involve primarily manufacturing settings where industrial machinery produces intense sound levels^[7], not uncommonly in the 75 to 85 decibel range. While this circumstance is the most dramatic, there are many other office type environments where sound levels may lie in the range of 70 to 75 decibels, entirely comprised of office equipment, music, public address systems, and even exterior noise intrusion. The latter environments can also produce noise health effects provided that exposures are long term.

In the case of industrial equipment, the most common techniques for noise protection of workers consist of shock mounting source equipment, creation of acrylic glass or other solid barriers, and provision of ear protection equipment. In certain cases the machinery itself can be re-designed to operate in a manner less prone to produce grating, grinding, frictional or other motions that induce sound emissions.

In the case of more conventional office environments, the techniques in architectural acoustics discussed above may apply. Other solutions may involve researching the quietest models of office equipment, particularly printers and photocopy machines. One source of annoying, if not loud, sound level emissions are certain types of lighting fixtures (notably older fluorescent globes). These fixtures can be retrofitted or analyzed to see whether over-illumination is present, a common office environment issue. If over-illumination is occurring, de-lamping or reduced light bank usage may apply.

Noise Pollution

Noise pollution (or environmental noise in technical venues) is displeasing human or machine created sound that disrupts the environment. The dominant form of noise pollution is from transportation sources, principally motor vehicles^[1] . The word “noise” comes from the Latin word nauseameaning “seasickness“, or from a derivative (perhaps Latin noxia) of Latin noceō = “I do harm”, referring originally to nuisance noise.^[2]

The overarching source of most noise worldwide is generated by transportation systems, principally motor vehicle noise, but also including aircraft noise and rail noise.^[3][4]. Hybrid vehicles are the first innovation within the last 100 years to achieve significant widespread noise source reduction.^{[citation needed]} Poor urban planning may also give rise to noise pollution, since juxtaposition of industrial to residential land uses, for example, often results in adverse consequences for the residential acoustic environment.

Besides transportation noise, other prominent sources are office equipment, factory machinery, appliances, power tools, lighting hum and audio entertainment systems. Furthermore, with the popularity of digital audio player devices, individuals in a noisy area might increase the volume in order to drown out ambient sounds. Construction equipment also produces noise pollution.

Noise from recreational vehicles has become a serious problem in rural areas. ATVs, also known as quads, have increased in popularity and are joining the traditional two wheeled dirt motorcycles for off-road riding.

The noise from ATV machines is quite different from of the traditional dirt bike. Some ATVs have large bore, four stroke engines that produce a loud throaty growl that will carry further due to the lower frequencies involved. The traditional two stroke engines on dirt bikes have gotten larger and, while they have higher frequencies, they still can propagate the sound for a mile or more. The noise produced by these vehicles is particularly disturbing due to the wide variations in frequency and volume.

Recreational vehicles are generally not required to be registered and control of the noise they emit is absent in most communities. However, there is a growing awareness that operation of these machines can seriously degrade the quality of life of those within earshot of the noise and some communities have enacted regulations, either by imposing limits on the sound or through land use laws. Rider organizations are also beginning to recognize the problem and are enlightening members as to future restrictions on riding if noise is not curtailed. because of human beings

Human health

Principal noise health effects are both health and behavioral in nature. The following discussion refers to sound levels that are present within 30 to 150 meters from a moderately busy highway. Sound is a particular auditory impression perceived by the sense of hearing. The presence of unwanted sound is a called noise pollution. This unwanted sound can seriously damage and effect physiological and psychological health. For instance, noise pollution can cause annoyance and aggression, hypertension, high stress levels, tinnitus, hearing loss, and other harmful effects depending on the level of sound, or how loud it is.^[5][6] Furthermore, stress and hypertension are the leading causes to health problems, whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.^[7][8]

Hearing

The mechanism for chronic exposure to noise leading to hearing loss is well established. The elevated sound levels cause trauma to the cochlearstructure in the inner ear, which gives rise to irreversible hearing loss.^[5]

The outer ear (visible portion of the human ear) combined with the middle ear amplifies sound levels by a factor of 20 when sound reaches the inner ear.^[9]

In Rosen’s seminal work on serious health effects regarding hearing loss and coronary artery disease, one of his findings derived from tracking Maabantribesmen, who were insignificantly exposed to transportation or industrial noise. This population was systematically compared by cohort group to a typical U.S. population. The findings proved that aging is an almost insignificant cause of hearing loss, which instead is associated with chronic exposure to moderately high levels of environmental noise.^[5]

Cardiovascular health

High noise levels can contribute to cardiovascular effects and exposure to moderately high (e.g. above 70 dBA) levels during a single eight hour period causes a statistical rise in blood pressure of five to ten mmHg; a clear and measurable increase in stress ^[10]; and vasoconstriction leading to theincreased blood pressure noted above as well as to increased incidence of coronary artery disease.

Annoyance

Though it pales in comparison to the health effects noted above, noise pollution constitutes a significant factor of annoyance and distraction in modern artificial environments:

1. The meaning listeners attribute to the sound influences annoyance, so that, if listeners dislike the noise content, they are annoyed. What is music to one is noise to another.
2. If the sound causes activity interference, noise is more likely to annoy (for example, sleep disturbance)
3. If listeners feel they can control the noise source, the less likely the noise will be annoying.
4. If listeners believe that the noise is subject to third-party control, including police, but control has failed, they are more annoyed.
5. The inherent unpleasantness of the sound causes annoyance.
6. Contextual sound. If the sound is appropriate for the activity it is in context. If one is at a race track the noise is in context and the psychological effects are absent. If one is at an outdoor picnic the race track noise will produce adverse psychological and physical effects.

A 2005 study by Spanish researchers found that in urban areas households are willing to pay approximately four Euros per decibel per year for noise reduction^[11].

Environment

Noise pollution can also be harmful to wildlife . High noise levels may interfere with the natural cycles of animals, including feeding behavior, breeding rituals and migration paths.^{[citation needed]} The most significant impact of noise to animal life is the systematic reduction of usable habitat, which in the case of endangered species may be an important part of the path to extinction. Perhaps the most sensational damage caused by noise pollution is the death of certain species of beached whales, brought on by the extremely loud (up to 200 decibels) sound of military sonar.^{[citation needed]}

Mitigation and control of noise

The sound tube in Melbourne, Australia, designed to reduce roadway noise without detracting from the area’s aesthetics.

There is also technology that has been applied with the aim of mitigating or containing noise as much as possible, provided that it has a sufficiently localized source.

? Roadway noise, is the most widespread environmental component of noise pollution worldwide. There are a variety of effective strategies for mitigating adverse sound levels including: use of noise barriers, limitation of vehicle speeds, alteration of roadway surface texture, limitation of heavy duty vehicles, use of traffic controls that smooth vehicle flow to reduce braking and acceleration, innovative tire design and other methods. Thousands of case studies in the U.S. alone have been documented starting in 1970, indicating substantial improvement in roadway planning and design. The most important factor in applying these strategies is a computer model for roadway noise, that is capable of addressing local topography, meteorology, traffic operations and hypothetical mitigation. Costs of building in mitigation is often quite modest, provided these solutions are sought in the planning stage of a roadway project.

? Aircraft noise can be reduced to some extent by design of quieter jet engines, which was pursued vigorously in the 1970s and 1980s. This strategy has brought limited but noticeable reduction of urban sound levels. Reconsideration of operations, such as altering flight paths and time of day runway use, have demonstrated significant benefits for residential populations near airports. FAA sponsored residential retrofit (insulation) programs initiated in the 1970s has also enjoyed widespread success in reducing interior residential noise in thousands of affected residences across the United States.

? Exposure of Industrial noise on workers has the longest history of scientific study, having been addressed since the 1930s. This scientific studies have emphasized redesign of industrial equipment, shock mounting assemblies and physical barriers in the workplace. Innovations have had considerable success; however, the costs of retrofitting existing systems is often rather high.

Legal status

Governments up until the 1970s viewed noise as a “nuisance” rather than an environmental problem. In the United States there are federal standards for highway and aircraft noise; states and local governments typically have very specific statutes on building codes, urban planning and roadway development. In Canada and the EU there are few national, provincial, or state laws that protect against noise. As a result in Canada and the EU, most regulation has been left up to municipal authorities.

Noise laws and ordinances vary widely among municipalities and indeed do not even exist in some cities. An ordinance may contain a general prohibition against making noise that is a nuisance, or it may set out specific guidelines for the level of noise allowable at certain times of the day and for certain activities. Exceptions are generally made for activities considered essential public services such as refuse collection and emergency vehicles.

Most city ordinances prohibit sound above a threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restricts it to a higher decibel level; however, enforcement is uneven. Many municipalities do not follow up on complaints. Even where a municipality has an enforcement office, it may only be willing to issue warnings, since taking offenders to court is expensive. For persistent nuisances, individuals may have to seek damages through the civil courts. Many jurisdictions, such as New York City and Chicago authorize police to impound cars with loud stereos and to hold the cars as evidence until the citation has been adjudicated.

Many conflicts over noise pollution are handled by negotiation between the emitter and the receiver. Escalation procedures vary by country, and may include action in conjunction with local authorities, in particular the police. Clear documentation, repetitive complaints, getting neighbors involved, and forming a Neighborhood Watch can be effective at obtaining enforcement. Noise pollution often persists because only five to ten percent of people affected by noise will lodge a formal complaint^{[citation needed]}. Many people are not aware of their legal right to quiet and do not know how to register a complaint. Furthermore, mobile noise sources are transitory such that they may be difficult to pursue unless a noise measurement device is in place, so effectiveness tends to depend on whether a city has instituted proactive enforcement policies (e.g. muffler inspections).

NOISE RATING CURVE:

Noise Rating Curve	Octave Band Mid-Frequency, Hz (dB refrence 0,00002 N/m2)
	31.5	62.5	125	250	500	1000	2000	4000	8000
NR 0	55	36	22	12	5	0	– 4	– 6	– 8
NR 10	62	43	31	21	15	10	7	4	2
NR 20	69	51	39	31	24	20	17	14	13
NR 30	76	59	48	40	34	30	27	25	23
NR 40	83	67	57	49	44	40	37	35	33
NR 50	89	75	66	59	54	50	47	45	44
NR 60	96	83	74	68	63	60	57	55	54
NR 70	103	91	83	77	73	70	68	66	64
NR 80	110	99	92	86	83	80	78	76	74
NR 90	117	107	100	96	93	90	88	86	85
NR 100	124	115	109	105	102	100	98	96	95
NR 110	120	122	118	114	112	110	108	107	105
NR 120	137	130	126	124	122	120	118	117	116
NR 130	144	138	135	133	131	130	128	127	126

Noise Reduction (NR)

The numerical difference, in decibels, of the average sound pressure levels in two areas or rooms. A measurement of “noise reduction” combines the effect of the sound transmission loss performance of structures separating the two areas or rooms, plus the effect of acoustic absorption present in the receiving room.

An introduction to the Noise Rating (NR) curves developed by the International Organization for Standardization (ISO).

• The Noise Rating (NR) curves are developed by the International
Organization for Standardization (ISO).

• Noise rating graphs are plotted of Sound Pressure Level at
frequency to show how acceptable sound levels vary
with frequency.

• What is acceptable varies with the room and the use of it.
There is a different curve obtained for each type of use.

• Each such curve is obtained by an NR number.

Noise Reduction Coefficient (NRC)

A measure of the acoustical absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05.

Non-Impulsive Noise

Includes: All noise not included in the definition of impulsive noise.

Octave

The interval between two sounds having a frequency ratio of two.- There are 8 octaves on the keyboard of a standard piano.

Octave Band

A segment of the frequency spectrum separated by an octave.

Octave Band Level

The integrated sound pressure level of only those sine-wave components in a specified octave band.

Office Noise Control Products

In today’s design-oriented world, acoustical products need to do more than function. They are expected to complement, and even enhance interior spaces. That’s why ArtUSA Industries is continually designing solutions with the results and look our clients are looking for. We offer a variety of impressive styles and colors. Our wall and ceiling panels are attractive and versatile, and include foam fabric-wrapped and metal panels. ArtUSA Noise Control Products, Inc. helps solve office noise issues in new and existing facilities with cost- effective, long-lasting and easy to install enclosures, ceiling tiles, wall panels, baffles, and other acoustical solutions. High levels of background noise and reverberation or echo hinder and interrupt workflow. So, what’s the solution? ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help offices sound better and work smoother. Lightweight and easy to suspend from high, open ceilings using traditional hanging or innovative cable suspension systems baffles absorb sound from all directions to reduce reverberation in large open office areas. Baffles are offered in a variety of standard and custom colors to complement or match school colors. Fabric-wrapped wall panel absorbs up to 85% of the sound directed toward it. They are available in hundreds of fabrics to complement new or freshen up existing color schemes. Ceiling tiles with a backer board drop into a standard grid system and help block sound traveling from adjacent rooms. Tiles without a backer board can be adhered to any wall or ceiling surface making them ideal for rooms without a grid system or those with low ceiling heights.

Oscillation

The variation with time, alternately increasing and decreasing, of (a) some feature of an audible sound, such as the sound pressure; or (b) some feature of a vibrating solid object, such as the displacement of its surface.

OSHA

The Occupational Safety and Health Administration.

Peak Sound Pressure

The maximum absolute value of the instantaneous sound pressure in a specific time interval. Note: in the case of a periodic wave, if the time interval considered is a complete period, the peak sound pressure becomes identical with the maximum sound pressure.

Period

The duration of time it takes for a periodic wave form (like a sine wave) to repeat itself.

Permanent Threshold Shift (PTS)

A permanent decrease of the acuity of the ear at a specified frequency as compared to a previously established reference level. The amount of permanent threshold shift is customarily expressed in decibels.

Permissible Noise Exposure

A permissable noise exposure issued by OSHA expressed in dBA.

Permissible Noise (OSHA)

DURATION PER DAY	dBA SLOW RESPONSE
8	90
6	92
4	95
3	97
2	100
1 1/2	102
1	105
1/2	110
1/4 or less	115 MAX

Phon

The unit of measurement for loudness level.

Pink Noise

Noise with constant energy per octave band width.

Pitch

The attribute of auditory sensation that orders sounds on a scale extending from low to high. Pitch depends primarily upon the frequency of the sound stimulus, but it also depends upon the sound pressure and wave form of the stimulus.

Plane Wave

A wave whose wave fronts are parallel and perpendicular to the direction in which the wave is traveling.

Presbycusis

The decline in hearing acuity that is attributed to the aging process.

Pure Tone

A sound for which the sound pressure is a simple sinusoidal function of the time, and characterized by its singleness of pitch.

Random Noise

An oscillation whose instantaneous magnitude is not specified for any given instant of time. It can be described statistically by probability distribution functions giving the traction of the total time that the magnitude of the noise lies within a specified range.

Reflection

The return of a sound wave from a surface.

Refraction

The bending of a sound wave from its original path, either because it is passing from one medium to another or by changes in the physical properties of the medium, e.g., a temperature or wind gradient in the air.

Religious Facility Noise Control Products

In churches, synagogues and worship centers large or small, words and music can sound incomprehensible to the congregation if sound is not properly controlled. Poor sound quality is common in churches because of an abundance of hard surface materials. Brick, marble, stone, tile, glass, wood and sheetrock are all acoustically reflective. Sound waves bounce back and forth between parallel surfaces, creating a confusion of noise until they finally decay. Even the most strategically-placed speakers and microphones will not compensate for poor acoustics. Every room needs some absorptive materials and some reflective materials to get the right acoustic mix for the room’s intended purpose. The challenge is to find that balance. Art-Fab and Art-Sorb panels from ArtUSA Noise Control Products Inc. are designed to absorb airborne sound energy and reduce a room’s overall noise, reverberation and standing waves—creating interiors that reduce the din without sacrificing the divine. The right balance between absorption and reflection using strategically placed acoustic wall panels and baffles, create a more enjoyable worship and listening experience. ArtUSA Industries affordable acoustic and sound control solutions are the proven answers to help the message and experience Lightweight and easy to install wall and ceiling treatments reduce reverberation and absorb sound from all directions. Traditional and or innovative solutions noise control and sound quality issues are our mission.

Resonance

The relatively large amplitude of vibration produced when the frequency of some source of sound or vibration “matches” the natural frequency of vibration of some object, component, or system.

Resonator

A device that resounds or vibrates in sympathy with a source of sound or vibration.

Reverberant Field

The region in a room where the reflected sound dominates, as opposed to the region close to the noise source where the direct sound dominates.

Reverberation

The persistence of sound in an enclosed space, as a result of multiple reflections, after the sound source has stopped.

Reverberation Room

A room having a long reverberation time, especially designed to make the sound field inside it as diffuse (homogeneous) as possible.

Reverberation Time (RT)

The reverberation time of a room is the time taken for the sound pressure level to decrease 60 dB from its steady-state value when the source of sound energy is suddenly interrupted. It is a measure of the persistence of an impulsive sound in a room as well as of the amount of acoustical absorption present inside the room. Rooms with long reverberation times are called live rooms.

RMS Sound Pressure

The square root of the time averaged square of the sound pressure.

Room Sound Propagation (Indoor)

The sound in a room will propagate to the receiver by direct sound and reverberant sound.

For a continuing source in a room, the sound level is the sum of direct and reverberant sound and is given by:
L_p = L_w + log (D / (4 p r²) + 4 / R) (dB)

where

D = directivity coefficient
R = room constant (m²)
r = distance from source (m)

Room constant:

R = S a_m / (1-a^m) (m²)

where

S = total surface of the room (m2)
a = absorption coefficient
a_m = mean apsorption coefficient for the room

Absorption coefficient:

a = Ia / Ii

where

I_a = sound intensity absorbed I_i = incident sound intensity

The rooms total absorption, m² Sabine:

A_m = S S a (m² Sabine)

The mean apsorption coefficient for the room a_m = A_m / S

The sound level as a sum of direct and reverberant sound for a source in a room

For a continuing source in a room, the sound level is the sum of direct and reverberant sound and is given by:

L_p = L_w + log (D / (4 p r²) + 4 / R) (dB)

where

D = directivity coefficient R = room constant (m² Sabine) r = distance from source (m)

Directivity coefficient:

The figure can be used to estimate the directivity coefficient D.

The figure permits calculation of theoretical sound pressure levels L_p, from both direct and reverberant sound, at a given distance (r) from a source inside room of sound power level L_w. R is the room constant.

Room Sound Propagation (Outdoor)

When the distance from the the power source doubles, the sound pressure level decrease with 6 dB. This relationship is also known as the inverse square law.

L_p = L_w
where

r = distance from source (m)
K’ = constant

When source radiates hemispherically with the source near ground K’ = – 8.
When source radiates spherically K’ = – 11.

Other factors affecting the radiation of sound might be direction of the source, barriers and atmospheric conditions.
The eq. can be modifyed as:

L_p = L_w – 20 log r + K’ + DI – A_a – A_b

where

DI = directivity index
A_a = attenuation due to atmospheric conditions
A_b = attenuation due to barriers

Root-Mean-Square (RMS)

1. The root-mean-square value of a time-varying quantity is obtained by squaring the function at each instant, obtaining the average of the squared values over the interval of interest, and then taking the square root of this average. For a sine wave, if you multiply the RMS value by the square root of 2, or about 1.41, you get the peak value of the wave. The RMS value, also called the effective value of the sound pressure, is the best measure of ordinary continuous sound, but the peak value is necessary for assessment of impulsive noises.

2. A term describing the mathematical process of determining an ‘average’ value of a complex signal.

Sabin

A measure of the sound absorption of a surface; it is the equivalent of one square foot of a perfectly absorptive surface.

School and Training Room Noise

A work group of the Acoustical Society of America (ASA) in conjunction with the American National Standards Institute (ANSI) recommends that classroom noise not exceed 35 decibels. Many American class- rooms today can be as loud as 50 decibels, for satisfactory communication, speech should be 15 decibels above background noise. The group also recommends that reverberation time not exceed O.6 seconds. Depending on its source, noise can be controlled by containing it, absorbing it, or both. Walls and ceilings treated with acoustic panels. They will absorb excess reverberation within a room. Noise from outside a classroom, whether from traffic or hallway conversation, can be contained with barriers installed within walls or above drop ceilings to block noise out. An ArtUSA Industries professional can help to identify your noise problem and offer the right solution.

Shielding

The attenuation of a sound, achieved by placing barriers between a sound source and the receiver.

Sone

The unit of measurement for loudness. One sone is the loudness of a sound whose loudness level is 40 phons. Loudness is proportional to the sound’s loudness rating, e.g., two sones are twice as loud as one sone.

Sociocusis

Loss of hearing caused by noise exposures that are part of the social environment, exclusive of occupational-noise exposure, physiological changes with age, and disease.

Sound

1. An oscillation in pressure, stress, particle displacement, particle velocity, etc., in an elastic or partially elastic medium, or the superposition of such propagated alterations.

2. An auditory sensation evoked by the oscillation described above. Not all sound waves can evoke an auditory sensation: e.g. ultrasound.

Soundproofing

Soundproofing is any means of reducing the intensity of sound with respect to a specified source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using barriers to block or absorb the energy of the sound waves, using damping structures such as baffles , or using active antinoise sound generators.

Soundproofing affects sound in two different ways: noise reduction and noise absorption. Noise reduction simply blocks the passage of sound waves through the use of distance and intervening objects in the sound path. Noise absorption, on the other hand, operates by transforming the sound wave. Noise absorption involves suppressing echoes, reverberation, resonance and reflection. The damping characteristics of the materials it is made out of are important in noise absorption.

Distance

The use of distance to dissipate sound is straightforward. The energy density of sound waves decrease as they spread out, so that increasing the distance between the receiver and source results in a progressively lesser intensity of sound at the receiver. In a normal three dimensional setting, the intensity of sound waves will be attenuated according to the inverse square of the distance from the source. Using mass to absorb sound is also quite straightforward, with part of the sound energy being used to vibrate the mass of the intervening object, rather than being transmitted. When this mass consists of air the extra dissipation on top of the distance effect is only significant for typically more than 1000 meters, depending also on the weather and reflections from the soil

Damping or Dampening is the process by which sonic vibrations are converted into heat over time and distance. This can be achieved in several ways. For example, use of a material such as loaded vinyl that is both heavy and soft, with the softness allowing it to damp the noise rather than allowing transmission. Making a sound wave transfer through different layers of material with different densities also assists in noise damping. This is the reason why open-celled foam is a good sound damper; the sound waves are forced to travel through multiple foam cells and their cell walls as sound travels through the foam medium. Improperly done, however, structural compliance can make things worse, enabling resonance. This process is analogous to a string holding wind-chimes: the string helps the chimes ring by isolating the vibration instead of damping it. Foam tapes may therefore be undependable in a soundproofing protocol.

Room Within A Room

A Room Within A Room (RWAR) is one method of isolating sound and stopping it transmitting to the outside world where it may be undesirable.

Most sound transfer from a room to the outside occurs through mechanical means. The vibration passes directly through the brick, woodwork and other solid elements. When it meets with an efficient sound board such as a wall, ceiling, floor or window, the vibration is amplified and heard in the second space. A mechanical transmission is much faster, more efficient and may be more readily amplified than an airborne transmission of the same initial strength.

The use of acoustic foams and other absorbent means are useless against this transmitted vibration. The user is required to break the connection between the room that contains the noise source and the outside world. This is called acoustic de-coupling. Ideal de-coupling involves eliminating vibration transfer in both solid materials and in the air, so air-flow into the room is often controlled. This has safety implications, for example proper ventilation must be assured and gas heaters cannot be used inside de-coupled space.

There are very successful professional products and methods available from ArtUSA Costs vary depending on the individual space.

Noise cancellation

Noise cancellation generators for active noise control are a relatively modern innovation. A microphone is used to pick up the sound that is then analyzed by a computer; then, sound waves with opposite polarity (not phase) are output through a speaker, causing destructive interference and cancelling much of the noise.

Noise barriers as exterior soundproofing

Since the early 1970s it has become common practice in the United States (followed later by many other industrialized countries) to engineer noise barriers along major highways to protect adjacent residents from intruding roadway noise. The technology exists to predict accurately the optimum geometry for the noise barrier design. Noise barriers may be constructed of masonry, earth or a combination thereof. One of the earliest noise barrier designs was in Arlington, Virginia adjacent to Interstate 66, stemming from interests expressed by the Arlington Coalition on Transportation. Possibly the earliest scientifically designed and published noise barrier construction was in Los Altos, California in 1970.

Sound Intensity

Power per unit area, vary substantially with distance from source, and also diminish as a result of intervening obstacles and barriers, air absorption, wind and other factors.

The intencity from a source pasing a spherical surface around the source can be expressed as:

I = W / A = W / 4 p r² (W/m²)

In a progressing leveled wave, intensity can be expressed as:

I = W / A = p² / r c (W/m²)

where

I = intensity of sound (W/m²)
W = power (W)
A = area (m²)
r = radius in the spherical surface (m)
p = root mean square pressure (N/m²)
r = density (kg/m³)
c = velocity of sound (m/s)

Sound intensity expressed in dB:

L_I = 10 log (I / I0) (dB)

where

I₀ = reference intensity (W/m²)

The normal reference level is 10^-12 W/m².

Sound Level

The weighted sound pressure level obtained by the use of a sound level meter and frequency weighting network, such as A, B, or C as specified in ANSI specifications for sound level meters (ANSI Sl.4-1971, or the latest approved revision). If the frequency weighting employed is not indicated, the A-weighting is implied.

Sound Level Meter

An instrument comprised of a microphone, amplifier, output meter, and frequency-weighting networks which is used for the measurement of noise and sound levels.

Sound Power

The total sound energy radiated by a source per unit time. The unit of measurement is the watt.

Sound Power Level

Sound power level are connected to the sound source and independent of distance. Sound power are indicated in decibel.

L_w = 10 log (W / W₀)

where

W₀ = reference power (W)

The normal reference level is 10^-12 W which is the lowest sound persons of excellent hearing can discern. Note that older american litterature may contain sound power level data referenced to 10^-13 W.

Sound Pressure

The instantaneous difference between the actual pressure produced by a sound wave and the average or barometric pressure at a given point in space.

Sound Pressure Level (SPL)

20 times the logarithm, to the base 10, of the ratio of the pressure of the sound measured to the reference pressure, which is 20 micronewtons per square meter. In equation form, sound pressure level in units of decibels is expressed as SPL (dB) = 20 log p/pr.

Since sound measuring instruments respond to sound pressure the “decibel” is generally associated with sound pressure level.

Sound pressure level quantify in decibels the intensity of given sound sources. Sound pressure level vary substantially with distance from source, and also diminish as a result of intervening obstacles and barriers, air absorption, wind and other factors.

Since I = p² / r c then:

L_p = 10 log (p² / p²0) = 20 log (p / p₀)

where

p = root mean square pressure (N/m²)

The usual reference level p_o is 20×10^-6 N/m².

• Note that the noise from fans, machines etc. in general are
documented in sound power level.

• If the sound pressure doubles,the sound pressure level
increases with 6 dB.

• The lowest sound level that people of excellent hearing can
discern has an acoustic sound power about 10^-12 W, 0 dB

• The loudest sound generally encountered is that of a jet
aircraft with a sound power of 105 W, 170 dB

Sound Transmission Class (STC)

The preferred single figure rating system designed to give an estimate of the sound insulation properties of a structure or a rank ordering of a series of structures.

Sound Transmission Loss (STL)

A measure of sound insulation provided by a structural configuration. Expressed in decibels, it is 10 times the logarithm to the base 10 of the reciprocal of the sound transmission coefficient of the configuration.

Spectrum

The description of a sound wave’s resolution into its components of frequency and amplitude.

Speech-Interference Level (SIL)

A calculated quantity providing a guide to the interference of a noise with the reception of speech. The speech-interference level is the arithmetic average of the octave band levels of the interfering noise in the most important part of the speech frequency range. The levels in octave bands centered at 500, 1000, and 2000 Hz are commonly averaged to determine the speech-interference level.

Speed (Velocity of Sound in Air

344 m/sec (l128 ft/sec) at 70 degrees F in air at sea level.

Spherical Divergence

The condition of propagation of spherical waves that relates to the regular decrease in intensity of a spherical sound wave at progressively greater distances from the source. Under this condition the sound pressure level decreases 6 decibels with each doubling of distance from the source.

Spherical Wave

A sound wave in which the surfaces of constant phase are concentric spheres. A small (point) source radiating into an open space produces a free sound field of spherical waves.

Steady-State Sounds

Sounds whose average characteristics remain relatively constant in time. A practical example of a steady-state sound source is an air conditioning unit.

Studio Noise

Designing an acoustically ideal sound stage, studio, control room or listening room is a challenge under any conditions. In the real world, where such rooms must fit into an existing building, the acoustical challenges are even greater. Three problems face the designer or acoustic engineer. Sound isolation Outside noise getting in. Automobile traffic, airplanes, footsteps, and conversation in hallways or adjacent rooms make it difficult to record quiet, clear musical passages and voices without sacrificing dynamic range. Noise and Vibration Control Building noise. Heat, ventilating and air-conditioning machinery generates sounds that range from a low-frequency rumble to a high-frequency hiss. Equipment noise. Cooling fans in PCs and studio equipment are another common source of unwanted sounds. With today’s digital electronic recording equipment, subliminally audible vibration and noise are likely to be recorded along with the artist’s performance. Room Acoustics Slap and flutter echo High-frequency sound information can lose clarity due to reflective delays caused by parallel hard surfaces in a live recording or listening environment. Near-field reflections. When hard surfaces are located close to the recording or listening position, reflected sound waves can have unpredictable effects on audio clarity imaging and frequency response. Room resonance. Room walls and floors often act as resonators or sounding boards at long wavelengths, causing amplification of bass fundamental frequencies and harmonics. Standing waves. When a sound’s wavelength coincides with the length of a room boundary the wave “stands.” This leads to boosting of certain frequencies and cancellation of others, especially at low frequencies where holes and spikes in frequency response are likely to occur. Live end/dead end” acoustics are created in control room settings by using sound-absorbing panels to treat the wall behind the speakers and a portion of the two adjacent walls, but leaving the listener area untreated or “live’: Studio acoustics are enhanced by treating three non-parallel surfaces, i.e. .two adjacent walls and the ceiling or floor. Unlike conventional materials such as acoustical tile, sponge rubber, cork or carpet, Our panels are engineered to absorb sound evenly over a broad frequency spectrum. Their engineered surface patterns dissipate and trap high-frequency sound energy while offering more absorptive area that conventional flat materials.

Tables of Acoustic Properties of Materials A widely used table from Specialty Engineering and Onda Corporation. We offer our list of material properties, complete with all of the updates. Materials are listed in order of hardness. If there is an abbreviation in one of the tables you do not understand, be sure to check in the abbreviations listing. Solids Longitudinal Piezoelectric Shear Piezoelectric Plastics Rubbers Liquids Gases Abbreviations References

The above list of tables open as pdf documents and require Adobe Acrobat Reader. Click here to download the latest version of the Reader or here to download Adobe Acrobat Reader version 5.1 for Windows 2000/XP.

If you feel the tables are not displayed properly (fonts), then download the latest version of the Reader.

If you are missing the Greek character font, you can download a ZIP-compressed copy of the .TTF font file.

If you are missing the Multinational Helvetica character font, you can download a ZIP-compressed copy of the .TTF font file.

Supplemental Tables

Laust Pedersen has kindly offered to include his list of material properties here as well, and rather than take it apart and edit everything into these lists, we offer it as a stand alone spreadsheet (MS Excel file in zip-format, for download only). We may, in the future, strive to incorporate these numbers into our own lists, but would like you to have the benefit of Laust’s work in the mean time.

Temporary Threshold Shift (TTS)

A temporary impairment of hearing acuity as indicated by a change in the threshold of audibility.

The ABCs of NOISE and SOUND CONTROL –

Just Remember the ABCs of Noise Control. The best way to control noise is Absorb it, Block it, Break up its path and isolate it or better yet a composite of them.

Absorb
Absorber products like the Acousti-Foam and Acousti-Panels work to control noise through absorption.

Block
Building a continuous barrier that traps or stops air movement greatly reduces airborne sound transmission. Steel Panels B 10 NR and acoustical seals reduce noise. [/one_half]


Composite of both to Break
Interior and exterior walls, ceilings, floors, all allow sound to travel between and through them. Using an acoustically resilient foam or clip in the assembly, and staggering openings such as windows and doors.

Composite of both to Isolate
Products like our enclosures and acousti-mat deaden noise and isolate or confine it to the area where it originated.