Soundproofing Glossary

Soundproofing and Acoustics: Industry Terms Defined

This glossary contains soundproofing and acoustic terminology, explanations and definitions (including acronyms) frequently used, in one place.

Absorption Panels: focused only on absorbing sound, as opposed to blocking it. Measured in Noise Reduction Coefficient (NRC)

Ambient Noise: background noise that naturally occurs in your home. This is the reason that actual results typically do not match laboratory results. Even if you can diminish outside noise from 60dB to 30dB, the fan whirring overhead will now be loud enough to hear and somewhat increase the new noise level.

Amplitude: loudness of sound, measured in dB. The decibel scale is a logarithmic scale; every time the decibel level increases by 10, the amplitude of the sound doubles. For instance, if it increases by 20, the sound is 4x as loud, and if the dB level increases by 30, it is 8x as loud.

Attenuation: the amount of sound lost through a surface. If the sound is 30dB coming into the surface, and 20dB afterward, the transmission loss was 10dB

CAC (Ceiling Attenuation Class): the STC rating for ceiling tiles and products.

CNEL (Community Noise Equivalent Level):The average noise heard outside of a home in an industrial or noisy area, over the period of a year. Loud noises at night are penalized double. The concept is used to determine how loud areas around airports and busy highways become. Some communities will offer financial assistance for soundproofing homes if the CNEL goes above 65 dB, or a locally mandated limit.

Damping: The cycle-to-cycle energy loss that occurs between waves. Over time, the wave will diminish naturally, as a grandfather clock’s pendulum slows naturally. You can add a destructive interference into the wave to make it decrease much more quickly (or almost instantaneously). This is done within a car’s muffler, but having a length as a fraction of the sound wave from the exhaust. Then, the wave’s crest interferes with its peak, to cancel out much of the noise that would otherwise exit the car into the environment.

Day-Night Level (DNL): Average Annual Sound Levels that represent the sound levels over a 24-hour period, while taking into account quiet periods as well as aircraft over-flights. For flights that occur after 10 p.m. and before 7 a.m., these events are counted twice. The DNL noise exposure contours in the residential neighborhoods are DNL 65 up to DNL 70. This is similar to the CNEL described above.

Diffusion & Diffuser Panels: breaking sound waves apart by splitting them into different directions. The panel is shaped so that incident (incoming) sound waves bounce off in all directions. This splits them up, so that the sound you hear is not as loud.

Flanking: The ability of sound to find the path of least resistance, passing around heavy, insulated areas into the adjacent rooms. When blocking sound, it is more like water than light – if there are any holes, the water will continue to flow until it has passed through the most easily.

Frequency: how quickly the sound wave repeats its movement, measured in Hertz, or per second. If the wave is measured at 1000 Hz, then it oscillates 1000 times per second. As humans, we perceive the frequency as “pitch”. The higher the frequency, the higher pitched noise that we interpret.

NRC (Noise Reduction Coefficient): ability to absorb sound, measured from 0-1. NRC is used to measure the ratio of sound absorbed to reflected. If a panel has an NRC of 1, then it absorbs 100% of the sound that comes into it, and reflects 0%. Sound can (and mostly does) still pass through the material, so it may bounce of the wall behind the panel. In general, this is important for loud noisy areas, like auditoriums and gyms, where an echo needs to be absorbed in order to hear the speaker.

Resonant Frequency: A specific frequency where the waves amplitude increases due to room geometry. At this state, the system is able to store vibrational energy. This is what happens when the perfect pitch is able to shatter a wine glass, because the wave hit at just the exact resonant frequency of the glass. Resonance is combatted by adding filters into instruments, or in the case of residential acoustics, by adding dampers or sound absorbers to disrupt transmission of resonant frequencies.

RWAR (Room within a Room): effectively creating a separate room within the room you are trying to isolate. This may be done around noisy machinery, as a small enclosure that essentially doubles the sound blocking. Additionally, if you need to soundproof further, you can apply the more expensive, soundproofing materials around the smaller room, which will reduce cost and save time.

STC (Sound Transmission Classification): This is a rating of how much sound is blocked by a material, averaged over a number of frequencies. Sound at high frequencies is easier to block, since it has shorter wavelengths. The material is tested at 8 different frequencies, and the average decibel loss over all 8 is the STC rating. A rough approximation is that STC rating is equivalent to the # of decibels that will be reduced by the curtain. Here are the STC calculations for the AcousticCurtain™.

Internationally, experts use the SRI (Sound Reduction Index) and OITC (Outdoor-Indoor Transmission Classification), based on the ASTM E-1332 Standard Classification for the Determination of Outdoor–Indoor Transmission Class.