Sound Absorption
The soundproofing treatment outlined here targets the control of unwanted sound reflections within a room. Before we proceed, we invite you to visit our courses here at the Academy on both Sound Reflection and the NRC to discover the behavior of sound wave reflection and how it is measured.
When an air borne sound wave hits a wall, a portion of that wave is returned to your room, while the balance of the wave will attempt to transmit through the wall. If the time elapsed between the original sound signal and the reflecting sound signal is greater than one tenth of a second, human ear will distinguish them as two separate sounds. This is called echo. But if the time elapsed is less than one tenth of a second, the reflecting sound is heard as one continuous prolonged sound. This is called Reverberation.
The length of time it takes for a sound reverberation within a room to die off to inaudibility is called the RT value of the room. RT stands for Reverberation Time. The industry standard is to measure the length of time a sound reflection will take to collapse by more than 60 dB from the strength of its original sound signal. This is called the RT60 value of the room. In an untreated room for sound control, the RT60 values can carry for up to 10 seconds or longer. The problem defined is that human ear can tolerate just 1.5 to 2.0 seconds worth of sound reverberation. Beyond this level, sound reflections become blurred, competing with new sound signals, and delivering unhealthy levels of what is called “background noise”.
Sound absorption treatments are designed to capture sound reflections and slow the room’s RT60 time down to under 2.0 seconds. By eliminating unwanted reverberation in a room, the background noise is cleaned out while better clarity is delivered from original sound signals such as speech patterns and blended harmonic musical tones.
Unwanted sound reflections within a room are caused by the lack of proper absorption coefficients on the existing surfaces in the room. Our Coefficients Chart illustrates the poor absorption qualities of standard wall, ceiling and floor spaces. On average, these surfaces will absorb less than 5% of the room’s unwanted energy, delivering back RT60 values that will average between 4 and 10 seconds. When we consider that sound actually radiates out like a pebble wave in a pond, all six surfaces in the room are accepting and reflecting unhealthy levels of sound reverberation as we simulate below. As you can see, untreated rooms are quick to fill with unhealthy levels of background noise.
Why Absorb Sound Reverberation?
Good quality sound absorption will serve to slow down sound wave reflections, cleaning out unhealthy levels of background noise in a room, while restoring the room back to good acoustic balance with good clarity to original sound.
For commercial settings, less background noise will trigger a more comfortable acoustic environment for groups of people that congregate in one room. No longer will people need to shout over the background noise to communicate. These are ideal conditions for fellowship halls, cafeterias, bars, restaurants, basketball courts, nurseries, night clubs, health clubs, dance studios, and multipurpose rooms. Classrooms will convert to more favorable learning environments, triggering better grades as a result of better communication from teacher to pupil. Sanctuaries and auditoriums deliver clear voice signals and harmonic musical tones that help sustain attendance. Office cubicle settings become more privatized, while recording studios, home theaters and broadcast studios all enjoy superior sound quality. Absorbing sound reflections can also lower decibel level exposures in unhealthy work environments that range from boarding kennels to industrial plants. The bottom line is that clearing out unwanted levels of background noise will improve the acoustic environment in most any room.
How it Works:
To improve the quality of sound produced within a room, we lower the RT time by increasing the absorption coefficients in the room as measured in Sabins. By placing NetWell sound absorption products in the room, Sabin counts are increased as sound reflections are captured. As the sound wave strikes against the material, tiny fibers or pores in the material accept the energy of the sound wave and begin to vibrate. This produces friction, which transforms the sound energy into a low grade form of heat called kinetic energy, which in turn will dissipate the energy up and out of the room unnoticed. What is delivered back into the room is a small percentage of the reflection that was able to escape. This process lowers the background noise in the room, and as a result, lowers the perceived level of sound. Note in the following chart how the sound pressure levels in a room drop as the ratio increases between a room’s “before” and “after” treatment for sound absorption:
In this example, suppose a room prior to a soundproofing treatment delivers 500 Sabins of absorption from the existing surfaces in the room. Following a NetWell treatment, suppose an additional 2000 Sabins are added into the room. The net effect of carrying 2500 Sabins in the room is five times greater than before the treatment. On the chart above, this factor of 5 is the Absorption Ratio along the bottom, which indicates a drop of 60% in perceived loudness in the room.
Product selection for your treatment is easy for our help desk to determine, but might prove overwhelming to the first time visitors to this website. Simply call us at 1-800-638-9355. Also, our Product Guide will list the hundreds of options available to you, while our Applications Guide can help you first select your treatment and then deliver you to the products best matched to your sound control project. As we discuss in our course on the NRC here at the Academy, the NRC value of a product also helps align the appropriate product to your treatment. In any case, please call our help desk to ensure you are targeting the right product for your treatment if you are a new customer.
Coverage:
Unlike the barrier treatments outlined in our course on Transmission Loss, absorption treatments do not require 100% coverage of a surface to trigger your results. Our goal is to collapse the RT time in your room down to under 2.0 seconds. The treatment will target a percentage of square foot coverage for your room, based on the size, shape, and surface texture of your room matched to the frequency of your sound source, and the thickness and NRC values of the product selected. Your goal is to then simply space the product around the room’s perimeter as best you are able. Though each room and each treatment is unique and should be confirmed with our help desk, the following coverage amounts can help serve as a guideline:
Room Description Suggested Wall Coverage
Classroom, Office, Fellowship Hall 15-20%
Home Theaters 25-30%
Recording Studios, Music Rooms 50-60%
Sanctuaries, Auditoriums, Gyms Sabin Formula
Remember that our goal with absorption is simply better control over your room’s environment, not a cure. This control is gauged by the degree of satisfaction you seek to attain. There are diminishing points of return in the art of sound absorption. If, for instance, you were to invest $3000 to trigger an 80% drop in your sound reflection and produce an RT time of 2.0 seconds, would you consider investing $15,000 to trigger an 85% drop in the same room to produce an RT time of 1.8 seconds? Probably not. The human ear is not fine tuned enough to be able to discern the difference for the additional cost. Our goal is to help you control both the reflections in your room and your pocketbook, and not to over sell you products that you don’t need. The averages listed above are just that. Some clients will prefer stronger coverage for a slight increase in their performance, while others match a pre-existing budget to determine their starting point. Your best advice is to follow the guidance available at our help desk.
Undertreating the Room:
Although we guard against the over treatment of your room, we also warn you about under treatment. If your application calls for the installation of 500 square feet of a product, and your budget allows for only 100 square feet, you will not get 1/5 the result. You may get 1/25th of the result. Absorption values accelerate as you move closer to the coverage amounts recommended. Although we are sensitive to the budgetary constraints of our clients, and do not have minimum orders, our goal has to be the protection of the reputation of our products. If a room is under treated, the products won’t perform.
Thickness:
As we outlined here in our course on the Hertz, sounds that produce low bass frequencies will produce longer, flatter sound wave patterns than higher-pitched tones. This allows bass frequencies to move more rapidly through surfaces with less time or distance traveled. As a result, this will lower a sound panel’s ability to capture and convert the sound wave. By thickening the panel, we increase the ability to capture the wave. As an example, let’s look at our Fabric Panels. The 2″ thickness boasts an NRC value at 125 Hertz of .46, while the 1″ thickness is just .11. The same product, twice as thick, produces four times the amount of absorption at the low bass frequency.
Product Placement:
One of the most frequently asked questions we get centers on the location of the product once the proper product selection and coverage amounts have been made. Remember that the sound reflections in your room are radiating like a pebble wave in a pond covering the equivalent of 3.5 football fields in less than 1 second. Every square foot of surface space in your room is getting hit with sound reflections faster than you can blink. So long as you follow our guidelines for quantities installed, your desired results can be triggered by simply spreading the product around the room as best you are able to. Remember, we are after better control here, not a cure. Align your treatment based on sprinkler heads, doors, windows, lighting, durability, and other factors that will be unique to your room. As long as the treatments are not hidden behind obstructions, the sound waves will find them and will be captured and converted.