A Crash Course In Classroom Acoustics
Everything You Wanted to Know but Were Afraid to Ask
Where to begin!
Evaluating a classroom or for that matter any other space, need not be as intimidating as most people would suspect, but a few hints and guidelines won’t hurt. If poor acoustics and excessive background noise in the classroom can interfere with speech intelligibility as all of the audio logical studies seem to indicate then you will need to know something about the nature of the noise in the room, its intensity, sources and effects. Once that is identified and quantified you can then make recommendations as to how the problems can be fixed and even quantify some of the potential results in doing so.
The new ANSI standards recommend that the background noise level in an unoccupied room should not be more than 35 dBA. That is about as quiet as an average living room with carpeted floors and no activity to speak of in the rest of the house. For most people 35 dBA is quiet. When we refer to dBA we are talking about the sound level in decibels (dB) in the A weighted scale. The A weighting is a scale that closely resembles how our ears perceive sound, that is to say it discounts the low frequencies since our sense of hearing is less sensitive to low-frequency sounds. That is a benefit since most building materials perform poorly when absorbing or blocking low-frequency noise.
When evaluating a room, the first step is to sketch out the dimensions, including the length, width, and height. It’s important to note the location of the doors, windows, and other fixtures, as well as the HVAC system. If the room has central HVAC, it is likely distributed through ceiling diffusers. In some cases, the system may be through unit ventilators located under the windows, or even window AC units. Good acoustics are important in any room, and to achieve this, consider using acoustic ceiling tiles or sound panels. Exterior noise level should also be taken into consideration. To ensure accurate recall of the room’s features, taking photographs can be helpful. These photos can also serve as a good reference for future evaluations.
The equal loudness contours provide an insight to how we perceive sounds at various frequencies and levels of intensity. This is an important element to keep in mind as we move forward and begin to learn more about sound and acoustical products.
Make notes, describe as accurately as you can what the walls are constructed of, what the floor covering is and what type of ceiling is present. If the ceiling is an acoustical ceiling, the acoustic tiles will be either, 12″×12″, 24″×24″ or 24″×48″. The latter two will most likely be installed in a Tee Bar suspension system. Note also the number of light fixtures and HVAC diffusers or speaker panels. Lighting fixtures with their acrylic face covers do not have the same acoustical value as acoustical tiles and often account for 10% or more of the ceiling surface. If the school is an older building be sure to see if you can tell if the ceiling tiles have been painted over the years, This is usually quite obvious and will give a clue to the fact that the acoustical absorbing qualities have been greatly diminished.
Be sure to consult with the custodian or the buildings and grounds person as they may be able to help determine the type of ceiling tile used, whether the walls are painted concrete block, drywall, plaster or some other material.
Most flooring products are either glue down direct carpeting or a hard surfaced floor tile. Glue down carpeting is generally not much more than an 1/8-3/16 of an inch thick. Carpet under padding is rarely used in school facilities.
Note the grade level of the classroom, if possible, when the school was built and the number of students in the class. Now you are ready to look and listen. Listen to any noises you can hear and focus on the source of the noise(s). Noise sources may be coming from the window area, the HVAC system, and the lighting ballasts or through the walls or doors. When you are concentrating on the sources and nature of noise it can be quite directional. Note your observations on your sketch.
The room you are evaluating should be as airtight as possible so if you can see cracks or holes in walls or the windows sound is going to leak into the room. The room is only as good as the weakest link. Many schools use folding doors between classrooms or demountable partitions that extend only up to the ceiling. If you can see light above the partition, there is a problem. Look to see if the partitions extend all the way up to the deck above the ceiling. You can do this by lifting out a ceiling tile and looking around above the ceiling. (Have the custodian help you) If you can see light from adjacent classrooms, there is a problem. The best construction techniques that will afford the best noise isolation are walls that extend from the floor to the underside of the deck above the ceiling. Anything less is likely to result in sound transmission problems and increase background noise levels.
Background Noise Sources:
- Through walls from adjacent classrooms.
- Over the ceiling from adjacent classrooms.
- Through doors, around the frame and under the door.
- Through ventilators or louvers above door units.
- Through HVAC ductwork from adjacent rooms.
- HVAC noise from ceiling diffusers.
- Through the light fixtures.
- From outside, through exterior walls and windows.
- From floor above.
In an unoccupied space, sounds can be heard from a variety of sources. Careful scrutiny of the room can lead to identifying the intrusive sources. The diagram illustrates a few of the most common sources of noise.
Trust your senses – you’ve likely noticed that there are sources of noise in the classroom, and you may have already pinpointed where they’re coming from. With all the information you’ve gathered, including notes, sketches, and observations, you now have a clear picture of the classroom that others can easily visualize. If the classroom is particularly noisy, consider using acoustic ceiling tiles or other noise-reduction measures to help the teacher’s voice be heard clearly by students. If possible, observe the classroom during an unoccupied period to get a better sense of the background noise level. By addressing these noise sources, you can create a better learning environment for everyone in the classroom.
Whether you are conducting a simple evaluation of the classroom acoustics or conducting a study involving any aspect of listening or learning in the classroom, it is important to describe the classroom. This is also true when evaluating FM Sound Field amplification systems. Sadly, I have read so many research papers that leave one wondering what the classroom and its acoustics looked like. Too many times the study conclusions beg the question, what did the classroom look like and how were the acoustics? Questions like, were the acoustics good and is that why the FM system performs as well as it does or conversely could the system have worked better if the acoustical issues had been addressed by improving the acoustical environment. Or, do FM Sound Field Amplifications work as well under dissimilar acoustical conditions and have such conclusions been documented? These concerns and observations are not raised to spark any controversy but rather to illustrate the need to be as thorough as possible in describing the architecture and the influence it has on the listening environment.
Taking Measurements – Background Noise Levels
Now you are ready to quantify the noise levels by taking sound level measurements. If you have a sound level meter, you know how to take measurements. When you do, mark the measurements on your plan and take several measurements throughout the room; an average sound level is generally what is needed. Be careful not to take measurements closer than three feet from the walls. When you subsequently include the sound level measurements in your evaluation report be sure to describe what you were measuring, if the measurements are an average and where the measurements were taken. Indicate the conditions under which the measurements were taken, i.e. unoccupied room, Air-conditioner or heating unit operating etc.
When evaluating the classroom for background noise to comply or compare against the ANSI standards, make sure that any electrically driven fixtures or equipment are turned off. Equipment and other fixtures are variables and should not be considered a part of the permanent building architecture. The HVAC should be operating, as this is a permanent part of the building architecture.
If you take measurements in the occupied classroom to ascertain the general noise levels during class time, again, be sure to note the position at which the measurements were taken, the number of children and teachers present and any equipment that might be operating. If you are going to take measurements to determine the Signal to Noise Ratio (S/NR) try to predetermine the exact location and distance that you want measurements at, ahead of time in order to minimize the disruption. If you are measuring the sound level of the teacher’s voice, it is good to establish the first measurement at about a three-foot distance from the teacher. Then you can compare the sound levels to the Inverse Square Law (Sound intensity diminishes by 6 dB with each doubling of the distance from the source)
Another variable that seems never to be mentioned in speech intelligibility studies is the level of the teacher’s voice. Not all teachers speak at the same level of intensity. Observe also, the teacher’s teaching style; does he/she turn his/her back on the students while talking. (There is a 10 dB reduction between facing the students head on and when facing away from the students). Does the teacher tend to roam around among the students? Observe the teachers speech delivery, does he/she speak quickly, slowly and annunciate the words distinctly. Slowing speech can improve speech intelligibility. Does the teacher have a heavy accent that might be alien to the student population? This may sound a little discriminatory but the objective is to provide the children with the best education we can. Finally, how is the discipline in the classroom; poor discipline leads to increased noise.
A segment of the sound wave front surface area increasinging with distance. In this angle, the same sound energy is distributed over the spherical surfaces of increasing areas a-s-d is increased. The intensity of the sound is inversely proportional to the square of the distance of the wave front from the signal source. Example: 1d-1, 2d-4, 3d-9, 4d-16
In general, when measuring sound in a room, we use the A-weighted scale to account for normal hearing sensitivity. However, it may be necessary to determine if there is a higher level of low-frequency noise present in the sound spectrum, particularly from HVAC systems which often generate such noise. If you can hear the HVAC noise, it is important to confirm its nature. One way to do this is to switch the weighting button or switch to the C-weighted scale, which accounts for low-frequency noise that is discounted in the A-weighted scale. By using the C-weighted scale, we can determine if the low-frequency noise is significant. If the C-weighted noise level is much higher than the same measurement taken in the A-weighted scale, it indicates a strong presence of low-frequency sound content. It is important to consider the equal loudness contour when assessing sound levels in a room, as reflected sound and direct sound can both affect the acoustic solution and overall room acoustics.
Many classrooms today have computers in the room that are left on most of the time. The CPUs frequently will have fans in them that are quite audible. Note where the equipment is located. Often the CPU is located in a corner or under a desk with adjacent hard surfaces that can reflect and amplify the sound toward the students. Many classrooms also have TV sets, often mounted in a corner close to walls separating classrooms. I have seen classrooms so equipped where the TV set in one classroom was closer to a student in the adjacent classroom than he/was to the teacher in that classroom.
Horror stories abound with respect to background noise levels, such as the Los Angeles Unified School District (LAUSD) who recently equipped hundreds of their classrooms with $400 million dollars worth of window unit air conditioners that had operational noise levels in the plus 50 to plus 60 dBA ranges. Sadly, the LAUSD knew about the ANSI standards but elected to ignore the standards and the scientific rationale that prompted their development.
Identification and quantifying noise levels is an important aspect to classroom evaluation in order to achieve a good signal to noise ratio. It is also important to for evaluation of a room to determine if the room is suitable for the application of Sound Field Amplification equipment.
Reverberation and Reverberation Time
Reverberations along with background noise are the two elements most frequently cited, that can have a negative impact on speech intelligibility. Reverberation is the persistence of sound in a room once the sound signal has abruptly ceased. Reverberation time is the time in seconds that it takes for the sound to die down by 60 decibels or put another way to 1/1,000,000 of its original intensity once the signal has ceased.
Sound propagates spherically in all directions, much like blowing up a very large balloon. Sound waves travel at about 770 miles per hour (1132 feet/second) in air and when the waves contact a hard surface they are reflected, time and time again until the sound energy is absorbed and can no longer be heard. Reverberation is much more audible in a large voluminous space like a gymnasium. It is quite easy to hear the reflected sounds in the form of a hissing or even a clicking sound. Any sound in an untreated gymnasium immediately sounds hollow or it echoes. The same is true even for smaller classrooms but is not quite as easy to detect. In continuous speech the reflections arriving at the student’s ear milliseconds after the direct speech sound tend to smear the clarity of the speech signal. You also need to recognize that beyond the critical distance of direct speech, the reflected sounds can sound louder than the direct speech signal.
Reverberation & Reverb Time
When reverberation occurs in a hard surfaced room the sounds can actually increase in intensity and is known as a sound build-up caused by the combination of direct and reflected sound energy. If you have ever driven through a tunnel with the windows down you will notice how much louder the sound is. Once again this is an increase due to the combination of direct and reflected sounds. It is not necessary to understand these phenomena as much as it is to recognize that they exist.
Reverberation is dependent on only two things, (a) the volume of the space and, (b) the amount of absorption in the space. As in the case of a large, hard surfaced gymnasium the RT is much longer.
Reverberation Time can be measured with sophisticated sound measuring equipment where the sound sensitive equipment measures the time it takes for a generated signal to decay by 60 decibels upon cessation of the signal. The SLM records the sound signal and decay times at all appropriate frequencies simultaneously. Reverberation Time can also be calculated with a surprising degree of accuracy manually or by a computer aided software program.
How to Calculate Reverb Time (RT)
The recommended RT for a typical classroom of 10,000 cubic feet or less, contained in the new ANSI standards should not exceed 0.6 seconds at each of the frequencies of 500 Hz, 1000 Hz and 2000 Hz. For classrooms between 10,000 and 20,000 cubic feet in volume, the RT should not exceed 0.7 seconds at the three frequencies.
The Sabine Formula for calculating the RT in a space is a simple mathematical formula presented as T= 0.049V/Sa where T is the reverberation time in seconds, 0.049 is a constant, V is the volume of the space, S is the surface area of all the surfaces and a is the absorption coefficient of the building material at a given frequency.
Calculating the RT manually can be rather tedious and somewhat time consuming but it can be done without too much difficulty. You will have to know what the absorption coefficients are for common building materials, which are readily available from a variety of sources. Practically all-acoustical materials have been tested and their manufacturers do publish the absorption coefficients. For the more common building material absorption coefficients a listing can be found at www.acousticalsurfaces.com under acoustics 101.
The acoustical absorption coefficient of a material is defined, as the incident sound that strikes the material that is not reflected. More simply put it is the percentage of sound of a particular frequency that strikes the material that is absorbed. Absorption coefficients range from 0.0 to 1.0. The higher the absorption coefficient the better the absorption. Frequently you will see acoustical materials that are described as having an NRC of, for example .65. The NRC or Noise Reduction Coefficient is a single number rating that is based on the average of the individual absorption coefficients at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz to the nearest 0.05. The higher the NRC, generally, the higher the absorption characteristics of the material. Many hard surfaces building materials will have an NRC of only 0.01 to 0.10 while highly absorptive materials that are soft and fibrous in nature will have an NRC of 0.90 to 1.00.
A more cost-effective method of calculating the Reverberation Time has been developed by the author, which is now available as a service from Acoustical Surfaces Inc., a Chaska, Minnesota based acoustical materials distributor. ASI will provide you with a questionnaire from which all of the required information is entered into a computer program and the RT is calculated on a worksheet and in report form. Known as RASP (Reverberation Analysis Software Program) the service is available for $200.00 for the first room analysis and $100.00 for each subsequent room on the same project.
In addition to calculating the RT of an existing or a proposed room, a second worksheet is also presented with acoustical recommendations on what options are available to correct the room acoustically to comply with the ANSI standards. Another feature of the program is the ability to enter background noise levels and distance factors in order to approximate the speech intelligibility as a percentage of speech understood correctly in accordance with the default data selected. When comparing an existing space with a treated space the program will also determine the decibel reduction of the reflected sound and further provides a graph from which the percentage of sound reduction as perceived by the human ear, can be charted.
The RASP program currently offered, as an acoustical analysis service may also be available as a user friendly, point, select, and click software program in the not too distant future. The program is designed to run on Windows and is not only a practical tool for calculating RT but is also an educational tool for designers and other persons interested in acoustics and sound. The author compared numerous calculated results with those of field-measured data. Not all classrooms are the same and so it was found that certain correction factors needed to be made with the result that the correlation between the two methods was surprisingly close. The ANSI standards cite the use of the Sabine Formula as a simple means of validating compliance with the standard.
Equally important to the data developed is the manner in which the data is presented so that it can be easily understood by most laypersons. A computer printout commands attention and respect for the data and may be much more meaningful than a bunch of numbers within a written report. Graphic Typical worksheet of RASP RT program.
Understanding the Data and Evaluating the Potential Solutions
The only sound that passes through a material is that which can snake through a leak in the material. When sound strikes a wall, the sound energy sets the wall in vibration, much like a radio signal to a speaker. The wall then becomes the transmitter and relays the signal on the opposite side of the wall, albeit at a reduced level of intensity. Some of the intensity of the sound signal will be lost in energy to heat conversion process as the sound waves energize the material.
In the case of acoustically absorptive materials such as acoustical ceiling tile or acoustical wall panels, the sound waves striking the material also cause the fibers to vibrate thereby creating and energy to heat conversion that reduces the sound energy. Acoustical ceiling tiles are the most commonly used acoustical materials because the ceiling area is normally the only available surface area that is not used for other purposes. Classroom walls often have to accommodate blackboards, doors or other wall mounted fixtures. Window walls have glass for light and a view. Floors need to be durable enough to walk on or locate furniture on. Ceiling surfaces are therefore the most logical surface to install acoustics. With sound bouncing around at 770 miles per hour the acoustical ceiling is going to be bombarded with direct and reflected sound waves where some percentage will be absorbed.
All ceiling tiles have one characteristic in common and that is that they are fibrous in nature though, some are better than others. The most common ceiling tile is made from a mineral fiber, which is relatively hard. The tiles are frequently perforated with a textured pattern. Other tiles may be manufactured from fiberglass and will be quite distinctive in their appearance either on the back or the edges. Some older schools may have the old 12″×12″ standard round hole perforations that are manufactured from wood or mineral fiber.
Most relatively modern ceiling tiles will be 2′x2′ or 2′x4′ in size and lay in a tee bar grid suspension system. Just because the ceiling is acoustical in nature, do not be deluded into thinking the acoustics are OK. They may not be, because the tile’s acoustical performance is not high enough to meet the recommended ANSI standards.
When evaluating the classroom for background noise, let us suppose that you have identified the problem as one stemming from the transmission of noise from other classrooms. It may be that the partition leaks because they only extend to the underside of the acoustical ceiling. The solution is to block the path of sound through the ceiling over the wall and back through the ceiling next door. Sealing any partition leaks with a gasket or caulking compound can solve this problem. Alternatively, barrier material can be installed in the ceiling space to block off the sound transmitting through the ceiling space. To be effective it has to be handled with detail but rest assured the problem can be resolved with relative ease.
The STC (Sound Transmission Class) is a single number rating that determines a structure’s noise blocking performance. The higher the number, the better the construction. The sound levels are measured at each frequency and the resulting noise reduction levels are applied to an STC chart similar to the inverse of the equal loudness contours. In other words, once again the low frequency sound levels are discounted to reflect how we hear.
Another way to evaluate the STC performance of a partition or wall is to set a radio in one room with the volume turned up to about 70 decibels and then go to the adjacent room and see if the sound can be heard easily. You can also measure the sound in the source room and then in the receiving room to determine the difference. This is known as the noise reduction of the wall but in reality it is the total noise reduction from one room to another by all pathways.
Recommended STC performance data for walls and floors between classrooms and other spaces are listed in the new ANSI S-12.60-2002 Classroom Acoustics standard.
As you look at the ceiling in a building that has central heating and air conditioning (HVAC) the problem could be due to noise from the ductwork or the ceiling vents. HVAC ceiling silencers are available to reduce this source of noise by way of sound reducing sound trap ceiling diffusers. The thing you need to know is that there are solutions and that help is available to determine which is the most cost effective solution. In some case HVAC noise may be nothing more than proper maintenance to the equipment or a matter of reducing the fan speed of the unit.
If the sound is coming through the windows, many times the windows simply need to be gasketed with an inexpensive foam seal. If the problem of sound intrusion is through thin glass it may be necessary to install a second layer of glass much like a storm window or screen. If the sound is coming through the door to the classroom, the door frame can be gasketed with a foam sealant and an inexpensive drop seal applied to the bottom of the door that drops down when the door is closed.
Many, many problems are simple problems to identify and fix when you know how. It is not a matter of rocket science but rather, more a matter of practical knowledge. That isn’t to say that there are not more serious problems that are more difficult to fix in which case you may need to resort to more extensive expertise.
Reducing Reflected Noise and Reverberation Time
Replacing old ineffective ceiling tile with a newer higher performing acoustical tile is an option and is easy to accomplish. Be sure to ask what the NRC values of the tile are, the higher the better.
If it is not possible to replace the ceiling tile or only a small amount of additional acoustical treatment is required to correct the room’s acoustics, consider acoustical wall panels.
Adding acoustical wall panels will reduce the reflected noise and also reduce the reverberation time. One thing you will not have to worry about too much and that is where to install the wall panels. In the average classroom with chalk and bulletin boards you will be limited thus the solution to where you can place the material is simply, “anywhere you can”. Sound waves generally make no great distinction as to where acoustical treatment should be placed; traveling at 770 miles per hour around the room the sound waves will find the acoustical material sooner rather than later. Generally speaking wall space is available up high on the walls often above the chalkboards; this is OK.
Sound Transmission Class (STC)
The Sound Transmission Class (STC or STC rating) is a single number rating of the effectiveness of a material or construction assembly to retard the transmission of airborne sound. The sound transmission loss between the source and receiving rooms are plotted on a graph by frequency and sound level in decibels. The STC curve is a sliding contour that is fitted to the performance data plotted in a manner that will allow no more than 32 deficiencies below the appropriate contour. The maximum deficiency at any given frequency shall not exceed 8 decibels. Once the appropriate contour has been selected the STC is determined by the decibel value of the vertical scale at 500 Hz. The STC is expressed as a single STC number (Example STC 32) Note that the STC contour is similar to the inverse of the equal loudness contour, insofar as it discounts the lower frequency sounds to reflect how our ears perceive the lower frequency sounds.
What Type of Acoustical Wall Panels Should You Choose
The following is a list of things to consider:
- Panel’s Material Composition
- Durability of the Material
- Ease of Installation
- Ease of Availability
- Acoustical Performance
- Flammability – Fire Safety
- Cost Effectiveness
The most widely used acoustical wall panels are fabricated from fiberglass with a decorative vinyl or woven fabric facing. They are acoustically effective but can be very expensive for a variety of reasons.
Foam panels, acoustically effective yes; lightweight yes; readily available yes. But they all are not fire safe and non-flammable. The gray convoluted foam panels made from polyurethane foam are inexpensive but they are also highly flammable and when they burn they are toxic to the point you can be dead before you hit the ground.
There are white melamine foam acoustical panels that are non-flammable but they are much more expensive and they simply are not durable and impact resistant.
A new acoustical material recently introduced into the marketplace is a high performance acoustical panel made from recycled cotton fibers called Echo Eliminator™. This acoustical material is relatively inexpensive, Class A non-flammable and is available in small sized panels which can be an ideal feature given the limited space available for panel application. The Echo Eliminator panels are extremely durable and abuse resistant. The panels are available in a range of colors. The Echo Eliminator panels can be easily installed with spray adhesive or can be mounted with Velcro or double faced tape for annual transfer from one classroom to another as a hearing impaired student graduates.
Most acoustical wall panels are available in several thicknesses with the most popular being 1″ or 2″. The acoustical performance of most acoustical panels is highly dependent on the panel’s thickness. A 1″ thick fabric faced fiberglass panel has an NRC of about .80 and a 2″ panel will have an NRC of 1.00. As we previously stated, the thicker the panel, the higher the acoustical performance. However thicker acoustical panels are not necessarily the best or most cost effective and the reason is the performance at particular frequencies. In most cases to achieve good speech intelligibility we need to concentrate on the speech frequencies of 500, 1000, and 2000 Hertz. At these frequencies a 1″ panel absorbs about 90-95% of the sound striking the panels. A 2″ panel by comparison will only absorb 100% of the sound striking it under normal circumstances. The cost premium for 2″ thick panels can be 40-50% more than for a 1″ panel. Doing the math, it is not cost effective to pay 40% more for only a 5-10% improvement in absorption.
The biggest advantage of a 2″ panel vs. a 1″ panel is the boost in acoustical absorption at the low frequencies when needed. Another thing to look at insofar as acoustical wall panels are concerned is the acoustical data. Many times you will see absorption coefficients at the different frequencies or the NRC that are greater than 1.00. That would suggest that the panel can absorb more sound than strikes the panels. The ASTM test procedure that governs the testing of acoustical materials contains a mathematical anomaly that can result in higher than unity data. ASTM requires the data to be presented as developed, but most acoustical engineers will round the data off to 1.00.
The absorption values are determined in the test laboratory by measuring the sound absorption of the surface area of 64 square feet of the material. The edges are blocked off. The absorption values therefore, are based on the acoustical performance of the exposed surface area and are reported for one square foot of material. Unless the acoustical data reported indicates otherwise, this is the standard reference for all acoustical materials as a nationally accepted standard as the means of comparing the performance of different products.
Having said that, there is also a little known acoustical phenomenon that teaches us that under certain circumstances, we can get a legitimate increase in acoustical performance for acoustical panels if they are installed individually with a space between the panels. If the acoustical panels are soft edged panels the edges can also absorb sound. Take for instance, a 1′×1′ square panel; the absorptive surface area is really 16″ by 16″ (12″ for the face area and two 2″ edge areas), do the math and you will find that the absorptive area is actually 1.78 square feet but you are only paying for 1 square foot of material. Just knowing about some of these acoustical phenomena will allow you to recommend what are the best buys and the biggest bang for the buck. Most acoustical sales people will not tell you this if in fact they even know about the “edge effect”.
As you compare acoustical panels be sure to look at availability and the ease of installation. The fabric or vinyl faced fiberglass panels are all custom manufactured. The cost of labor to apply decorative fabric facings and harden the edges can be expensive and about the same as for a much larger sized panel, thus the cost can be substantially more for smaller sized panels than for a larger one, which may not fit into the available wall space. Foam panels are easily available and can be shipped to your school by UPS, as can the Echo Eliminator panels, which are also available for same day shipment.
Some Other Things to Keep in Mind
While typical classrooms may be your main concern there are many very noisy spaces in schools. Gymnasiums are notorious for being noisy as are many lunch rooms, swimming pools, industrial arts rooms and band rooms.
The sound level of a Phys-Ed instructor’s whistle in a reverberative gymnasium can be 130 decibels in his/her ear canal. Clearly, this is too loud and can lead to noise induced hearing loss.
Band practice rooms can also be noisy with sound levels reaching in excess of 100 decibels and band directors who take no precautions can also sustain noise induced hearing loss.
Most people do not understand the science of sound; as a branch of physics, acoustics can be quite intimidating to many people. Hopefully this article will take some of the mystery and intimidation out of the acoustics agenda. At times acoustics can be quite mysterious and intimidating with gruesome mathematical equations that can strike fear into the stoutest of hearts. That said, we all know more about noise and acoustics than perhaps we realize; we all know excessive noise when we hear it and we can easily measure it, if in fact we want to quantify it. So when all is said and done, evaluating classroom and other spaces is more a matter of common sense when you know how. This article does not cover all of the noise conditions you might run into from time to time but hopefully it can be a resource for you to follow when asked to evaluate a classroom or other school space.
When you have all of the elements of your classroom evaluation put together, why not present it in an inexpensive clear plastic presentation folder. Now you have developed a professional looking, world class report.
Mike Nixon, has been a subscriber to EAA for a number of years. He is also the moderator for the Classroom Acoustics listserv, a familiar resource to many EAA members. He has been a long time advocate for improving classroom acoustics and served on the ANSI classroom acoustics working committee. As a technical consultant to Acoustical Surfaces Inc a Chaska, Minnesota based acoustical materials and consulting services supplier, he has assisted ASI to develop unique and cost effective acoustical products and service for educational facilities nationwide.