Noise and Sound Control for Classrooms & Training Rooms by ArtUSA
A Sound Environment
In order to improve learning, productivity,
concentration, and teacher – student communication, you need to control the
background noise and reverberation level within the classroom. ANSI Standard
S 12.60-2002 American National Standard Acoustical Performance Criteria,
Design Requirements, and Guidelines for Schools now recommends maximum
background noise at 35 decibels and reverberation at 0.6 to 0.7 for unoccupied
classrooms. No matter how hard students try to concentrate on the teacher's
instructions, they can't help but be distracted by noise. Their concentration
levels are affected by sounds that come from inside and outside the classrooms.
We have products that will reduce the background noise and absorb the echo and
reverberation within school classrooms, gymnasiums, auditoriums, cafeterias, or
anywhere you have a noise problem. We can help you improve teacher – student
communication, thereby increasing student learning productivity. Our noise
control products are effective, cost efficient, and easy to install.
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 panels absorb
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
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
Acoustics Classroom design and layouts with good acoustics help students understand what
educators are teaching and allows students to have a better understanding of the
lessons with fewer distractions. Proper design and layout in a classroom
environment will add acoustical wall panels or acoustical ceiling tiles to break
up the hard wall and ceiling surfaces used in typical classroom environment.
Multipurpose Rooms The goal of noise reduction in large open rooms is to add sound
absorption materials to reduce reverb within the room. Typically these large
rooms have hard reflective walls and floors such as concrete block and there is
a need for noise reduction. Adding noise control products such as hanging
baffles or wall panels will increase speech intelligibility and reduce ambient
noise during events for greater usage of the room. These sound absorption
materials should be planned into the design of the gym or multipurpose room,
however they can be added as a retrofit application as the need for noise
reduction within the facility is addressed.
||Swimming PoolsDuring the
design and construction phase of an indoor swimming pool planning should be done
to control the ambient sound within the room. Most indoor swimming pool designs
call for very hard reflective surfaces such as painted block walls and metal
ceiling decks. Add to that the reflectiveness of the water and you will have
problems with excessive reverb within the room. The goal during the design and
construction phase of a swimming pool should be to add sound absorbing materials
to reduce the reverberation (echo) in the room. Materials such as acoustical
blanket or sound curtains and baffles work well to reduce the reverberation
within the room and add color to the walls and ceilings within the indoor
The teleconference room, an important part of the audio circuit, demands adequate acoustical treatment of all room surfaces.
The slightest echo can undermine speech intelligibility.
Reverberation reduction may require significant sound absorption material.
Most offices and conference rooms are too noisy and too reveberant to serve as teleconferencing rooms.
The teleconferencing room should be designed as a package with the aid of a professional acoustical consultant, especially when an upscale interior design is required.
Teleconferencing rooms, webcasting rooms and distance classrooms all require the same considerations for noise as traditional broadcasting rooms. Acoustically there are two main areas for consideration. First is noise coming in the room from the outside. Second is to keep the reverberation of the sound inside the room down to a level where the microphone doesn't "hear" reflections causing a hollow or echoic sound that limits speech intelligibility.
Noise Criteria of 20 decibels (NC-20) should exist in the broadcasting room. This means when the room is empty and quiet the sound pressure level in the room is 20 decibels or less. The existing conditions in most cases make achieving this level a challenge. Common noises that create problems are heating & air conditioning systems, telephones ringing or people talking in the next room, office equipment, and traffic noise coming from the street.
Speech Intelligibility in broadcasting requires a Reverberation Time of .75 to 1 second. Reverberation Time (RT60) is the time it takes for noise to reduce in volume by 60 decibels.
Untreated rooms have a variety of reverberation times depending on the size and shape along with the absorptive qualities of the surfaces in the room. Generally, you can expect your room to require additional absorptive materials on the walls, ceilings, floors and/or other reflective surfaces, such as tabletops and file cabinets. Existing reverberation times can be calculated. The amount of absorptive material needed to reduce that time to the recommended RT60 can also be calculated. Once this criteria is established acoustical materials and location can then be specified.
If you are considering installation of a teleconferencing room, webcasting room or distance learning classroom, you should consult with a qualified acoustical designer, as early as possible, to assure your room selection is the optimal location to avoid existing problems. If the location of your room has already been established, your acoustical designer can assist in determining the layout and orientation of monitors, speakers and microphones, as well as other acoustical considerations that will assure the best possible design.
In most applications, Acoustical Treatments are more effective and less expensive when a qualified acoustical designer is consulted early in the process of developing your plan
Noise Control in a nutshell (for existing buildings)
Some spaces are not primarily designed with an acoustical function, but acoustics impedes other functions: these spaces are just too loud. The acoustical requirement for noisy spaces, such as cafeterias, work spaces, gymnasiums, and pools is straightforward: make them less noisy. There are two ways to accomplish this goal:
1. isolate the space from noise sources;
2. reduce reverberation.
It is always better, if possible, to control noise by removing a noise source. In the case of a cafeteria or gymnasium, however, the largest source of noise, people in the space, can’t be removed. However, there may be other sources of noise that can be removed to make these spaces quieter, such as air-conditioning units and – very common – drink vending machines with loud, built-in refrigerators.
Changing room surfaces to reduce reverberation is often the only practical solution for quieting a noisy space. The basic problem is to determine how to get in as much sound-absorbing material as possible at a reasonable cost while preserving aesthetics.
ASA Group Works to Establish Minimum Classroom Noise Standards
Proposed standards for classroom acoustics are being developed. 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.
Cafeterias are often synonymous with noise. If you do an Internet word search on "cafeteria noise" or "noisy or loud cafeteria" you would find over 200 entries. A search on "quiet cafeteria" turns up about 40. Dictionaries often use noisy cafeterias as an example of the use of the adjective noisy. Those who study the ability to understand speech in noise often use what is called "cafeteria noise" as the noise source. It is a recording of many people talking at the same time.
This is especially true of the school cafeteria. Parent Teacher Associations (PTA's) and others call acoustical consultants looking for answers to this problem. Some cafeterias exceed the OSHA noise level of 85 dBA and causing cafeterias to begin accumulating noise dose. When visiting and measuring noise at one school, a frustrated teacher screamed into the microphone on the sound level meter (paraphrased) "It sure is loud in here isn't it?"
So what is the primary underlying phenomenon? Research has shown that signal to noise ratio (S/N) is the number one factor contributing to changes in voice levels used by adults. S/N is simply the difference in sound level between the signal (what someone wants to hear) and the background noise (what is interfering with someone hearing the signal). The S/N in a cafeteria is the difference in sound level of the person talking to the noise of everyone else talking measured at the listener's ear. When the S/N is poor, someone cannot be heard over the "cafeteria noise", the response is often to raise one's voice. This makes sense, after all S/N is also the primary factor affecting speech intelligibility (the ability to understand speech) in this setting. It has been thought that adults will all then raise their voices to some maximum sustainable voice level, until listening conditions improve again.
S/N in a cafeteria is controlled by the number of people talking, the total sound absorption in the room (some surfaces absorb sound, some mainly reflect sound), and the seating density (how close the different noise sources are). We know that small changes in S/N can result in large changes in the understanding of speech. This could possibly mean people may modify their voice levels in response to even small changes in S/N.
Why are some restaurants quiet and school cafeterias noisy? For starters, classroom acoustics research has shown that children have a much greater difficulty understanding teachers and each other in noise and reverberation than adults do. Reverberation is the time rate of sound decay in a room. It is the liveliness or 'echoey' (made up word) character that is found especially in large rooms with mostly hard surfaces such as the typical large gym. In addition, the number of children in a cafeteria and seating densities are much greater than in adult cafeterias and restaurants. Quiet restaurants and adult cafeterias also have full acoustical ceilings, carpet, and padded furniture. Most school cafeterias have no more than a basic acoustical ceiling with mediocre sound absorption properties. Less absorption, more people talking, greater seating densities, and greater inherent difficulty understanding speech all mean much louder cafeterias.
What can be done about it? There has been anecdotal evidence that adults respond to improved S/N by lowering their voices, even if conditions are still not ideal. If this is true, and if it is also true for children, it could mean that, even a small improvement in S/N would result in children also lowering their voices, and therefore lower noise levels. To test this idea, noise levels and other relevant information to determine the acoustics of the space were collected and analyzed from 19 schools, of which 13 were elementary schools. 5 minute median broadband A-weighted noise levels varied from the lower 70's (dB) to the upper 80's (dB). The analysis of the data showed that children's voice levels are strongly a function of S/N. Reverberation may also have a lesser role. Reverberant spaces also tend to have poor S/N making evaluation difficult. This work showed that better acoustics (better S/N) result in less noisy cafeterias and children using lower voices.
How can the S/N be improved? S/N can be improved by reducing the number of children talking (quiet periods, reading time etc.), reducing the number of children, adding sound absorption, or having a lower seating density. Many of these and other ideas can be implemented in designing better school cafeterias in initial construction. For instance, the use of more absorptive and full acoustical ceilings, and the addition of absorptive wall treatments. Reduction of seating densities. Reducing the number of kids talking may involve having outdoor play areas, or spreading lunch service over a larger period. With existing schools, often answers are limited to looking at adding sound absorption.
This is what happened at Dillard Drive Elementary School in Raleigh, North Carolina. The A-weighted noise levels were generally above 80 dB and up to 86.5 dB for 5 minutes at a time during recent measurements (even higher during the larger study last year). This school had the highest 5-minute median sound levels in the study. The room had up to around 230 children at a given time with a seating density as little as under 15 sq.ft. per person. The only absorptive surface (other than the kids themselves) was a partial acoustical ceiling that had very mediocre sound absorption (probably chosen for fire-rating, not acoustical quality). The room was very reverberant when empty. It was a day lit room with a high ceiling (over 30 feet in height at it's peak). The fire rating required in the existing ceiling made replacing the panels with a highly absorptive (lower fire-rated) fiberglass panel not feasible. Instead, a fiberglass ceiling was added in a lower ceiling area and similar fiberglass panels added to the walls. Armstrong provided the material. If children did not change their behavior, the treatment (calculated) would have reduced levels only 1.7 dB. Instead, levels were reduced between 3-3.5 dB. This can only be from reduced voice levels. This 3-3.5 dB is typically considered a barely noticeable change, but remember what a small change in S/N can do. So far, many at Dillard feel it was a definite improvement. One teacher felt she can now actually tell who is talking too loud and correct them. One of the PTA members shared high praises about the change. Of course, with that small a change in sound level, some have not noticed as much a change. The data from the other schools suggested a 5 dB change (instead of 3-3.5 dB) would result. The Dillard measurements after room modifications clearly is not typical of the other data collected. It may be that the children will adjust their voices further as time progresses.
So the answer to the question: Are all school cafeterias created equal? NO. Although quiet cafeterias may be too much to ask for, certainly less noisy and more pleasant school cafeterias are achievable.
Gymnasiums, multipurpose rooms and meetings halls are typically large, noisy rooms, with numerous solid surfaces. The "hard" surfaces create significant levels of reverb (echo) which raises the overall noise level to a point where communication and speech clarity become very difficult. The key to controlling the sound in these rooms is to lower the reverberation time, or the amount of time it takes for the sound to decay. To improve acoustics in gyms, multipurpose rooms and meting halls, it will require the addition of noise absorbing materials.
ArtUSA Noise Control Products, Inc. has a complete line of acoustical materials designed for use in high-traffic, loud environments such as gymnasiums, multi-purpose rooms, and meeting halls. Our products meets fire code requirements, provide excellent durability and the best acoustical performance available.
We ship our products factory direct. Contact our Acoustical Consultants for expert advice on your project. ArtUSA Noise Control Products, Inc. can provide cost effective sound solutions that work.
The Secret of Architectural Acoustics Revealed
Have you ever noticed that your radio seems awfully loud when you stop your car after listening on the highway? Or have you ever felt that palpable relief when the air conditioner shuts off? We don't notice background noise---but background noise determines what we can hear and understand in the foreground.
Some times we don't want to hear everything. Imagine if you could hear and understand every conversation at your office. It would be terribly distracting. But when we do want to hear every little thing---at a religious service, in an important meeting, at a play, or at a concert---background noise is critical.
During a lecture or sermon, any audible sound not made by the speaker is noise; during a performance, any audible sound not created by a performer is noise. There are, of course, many aspects to excellent acoustical design. However, in any space intended for listening, strict control of noise is fundamental. I call these spaces "critical-listening space."
Sources of noise include traffic, airplanes, machinery, plumbing, lights, and people in other spaces. In a space for listening, the worst offender is usually the heating, ventilating, and air-conditioning system (HVAC).
The (undamaged) human ear is so sensitive that we can detect sounds that displace the eardrum by roughly the diameter of a hydrogen molecule.1 This means that background noise determines the softest sound that a performer or speaker can effectively utilize. Even in spaces that most people would consider quiet, the background noise level can be twenty to thirty decibels above the threshold of hearing. You don't notice this, but the performer has lost twenty to thirty decibels of dynamic range!
This is illustrated in the graph below, with HVAC noise criteria curves for comparison.2
NC-40 is considered acceptable for such noncritical spaces as lobbies and corridors. NC-30 would be acceptable for a motel room. NC-20 is often given as acceptable for churches or drama theatres.3 But look at how much area there is between the threshold of hearing curve4 and NC-20. There is an awful lot of audible sound being covered up by an HVAC system at NC-20.
When a theatre is truly quiet, an actor can use his entire dynamic range, from a shout to a whisper, and still be clearly understood. Since the quiet moments in a drama are often the most electrifying, strict control of background noise is essential.
The ancient Greek theatres are known for their almost magical acoustics for speech. One can hear a drachma drop from the farthest seats in the theatre at Epidaurus. How can this be so? The answer is that no audible sound covers up the sound of the coin striking stone--and so it is heard.
Similarly for music, a silent background allows a performer to exploit his entire dynamic range. The loud climaxes of a musical performance can be wonderfully stirring, but the quiet moments set off these climactic moments and give them their power. Without the quiet moments, music is all on the same dull level. Furthermore, some of the most intense, magical moments in music are the softest. These moments are only possible when the hall in which they occur is truly quiet.
Recording engineers understand this. They commonly turn off all mechanical systems and most lights while recording.
Speech and Music in the Same Space
Many spaces are used for both speech and music, the best example being church sanctuaries. For such mixed use, a silent background is particularly important. This is because reverberation (the persistence of sound in space) is necessary for music. Without reverberation, music sounds flat and dull. But reverberation can interfere with speech intelligibility by prolonging the sounds of speech, smearing them in time.
A good speaker corrects for this effect by speaking slowly and clearly, working with reverberation to enhance the sound of his voice. However, reverberation amplifies background noise, creating a double difficulty for speech. Contrary to common belief, speech can work quite well in a properly designed reverberant space, but only if background noise is minimized.
Audience noise is beyond the direct control of the architect or acoustical consultant. However, research shows that audience members are significantly quieter when background noise levels are very low. In the City of Birmingham Symphony Hall, Birmingham, England---a hall with exceptionally low background noise---audience members are so attentive during quiet music passages that they hold their breath to listen.
Examples of Spaces with Low Background Noise
- Meyerson Symphony Hall, Dallas
- Domain Forget, Charlevoix Quebec
- New Jersey Performing Arts Center, Newark, NJ
- Clemens Theatre, Christopher Dock Mennonite School, Lansdale, PA
Gymnasiums, Restaurants, Cafeterias
Listening may not be the primary function in your space. However, people are always hearing, and the acoustics of these spaces can almost always be improved by lowering background noise (as well as other measures). I was recently in a gymnasium, for instance, with horrible screeching noise from the lights. The poor gym teacher who has to work in that space must have a perpetual headache.
The Common Condition
In the vast majority of places where I listen---churches, theatres, lecture halls, recital halls, concert halls---background noise imposes a haze in front of the sound. This noise itself goes unnoticed by most people. Instead, they notice that their experience is diminished: the tone color of the violins is dull; the sound lacks clarity; they can't quite understand the words.
The usual response to the ubiquitous blanketing of desired sound by background noise is to turn up the amplification. Amplification often adds fifteen to twenty decibels above the background noise to the level of the speaker. Wouldn't it be better to reveal the speaker by removing twenty to thirty decibels of background noise?
Furthermore, lower background noise makes the job of the sound system vastly easier.
See and Hear for Yourself
The effect of background noise can be compared to looking through a dirty window; one doesn't notice the dirt on the window, one simply can't make out the view. Clean the window for a striking improvement in clarity. And so it is when background noise is controlled. You can hear this for your self by the following simple experiment. You need two other people to help.
- Two people stand on opposite ends of the room.
- The third person is on hand to manage the noisemakers: fans, ventilation systems, lights, dimmer racks, air-conditioning, etc.
- Turn on all noisemakers. In actual practice not all these devices may be on at the same time, but for the sake of demonstration turn them on to create the greatest contrast.
- Converse with the person across the room. Note the effort necessary to make yourself understood. Note the effort necessary to understand.
- Turn off all the noisemakers at once.
- Proceed with your conversation.
- Note the change in effort necessary to understand and be understood.
Even in rooms that have other acoustical difficulties, the improvement should be clear and palpable.
What Is To Be Done?
When designing a new critical-listening space, consider the location of noise producing machinery such as air-handlers, and the design of a silent mechanical ventilation system from the very beginning. Few people realize that it is possible to supply cool air to a room without creating any noise. It is. However, since this is not the usual practice, such a silent system must be considered from the beginning of design.
An architect once called me to help with the design of a high school auditorium. I discovered that it was too late in the design to move two large air-handlers from their location on the roof of the auditorium. They might just as well have been put on stage! I did my best to help out, but nothing I could recommend for the inside of the room will cancel out the deleterious effect of those two huge noisemakers.
In the case of historic renovation, noise control may be the only option available for improving the acoustics of a space. In some cases, merely quieting a noisy mechanical ventilation system will affect a drastic improvement in the acoustics.
Conversely, many a perfectly lovely space has been ruined acoustically by loud new ventilation systems. When planning the renovation of a worship or performance space, make noise control the first consideration.
Noise control is fundamentally important to the success of any building for listening. It can make the difference between excellent sound and the usual mediocrity. This is especially true on a tight budget. Better to save money by leaving out the seats! After all, these buildings are often meant to last for more than a hundred years.
Since the level of background noise determines what we can hear in a space, it determines the level of acoustical excellence. This is truly the secret of great acoustics. Awareness of this secret in the early stages of design brings excellent acoustics for your new critical-listening space within your grasp. (by Orpheus Acoustics)
Quiet Classrooms is an alliance of non-profit organizations working to create better learning environments in schools by reducing noise. Quiet background noise levels and good classroom acoustics are important for good learning. This is true for students in general and hearing impaired students in particular. This website is a resource for schools, school boards, P.T.A.s, principals, parents, teachers, students, and school architects