ACCEPTABLE
SOUND LEVELS

Acceptable sound levels in different location such as kindergartens, auditoriums, libraries, cinemas ...
according to the ETB

Octave	Frequency (Hz)	Wave Length in air (m)
1	63	5.46
2	125	2.75
3	250	1.38
4	500	0.69
5	1K	0.34
6	2K	0.17
7	4K	0.085
8	8K	0.043

 A    B    C    D     E    F    G     H     I    J    K     L     M 
 N    O    P     Q    R    S    T     U    V    W    X     Y    Z 

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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

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.

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 pa