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Acoustics 101: Key Concepts and Definitions

Acoustics can have an impact on a built environment in many ways. Understanding how your building materials and design can control these factors are key in creating a successful acoustical design.

But before you can make those decisions, it’s equally important to understand the terms pertaining to acoustics. This will not only keep you informed on the specifics of acoustics in construction, but it also allows for more informed decisions when specifying products for their latest project.

Sound Absorption

Sound absorption is necessary to reduce the reverberation in a space, which can improve the clarity of speech while reducing excessive noise within a room.

Sound Transmission

Airborne or structural sound transmission must be reduced to prevent sound from traveling between two spaces.

Noise Reduction Coefficient (NRC)

NRC is a single-number rating for comparing the sound absorption of building materials. Products with a high NRC value absorb sound and help reduce reverberation.

Ceiling Attenuation Class (CAC)

CAC is a single-number rating for comparing sound attenuation of ceiling systems. Products with a high CAC value can help reduce sound transmission between rooms that share a ceiling plenum.

Sound Transmission Class (STC)

STC is a single-number rating for comparing sound attenuation of partitions, such as walls or floor-ceiling assemblies. Higher STC values translate to a greater attenuation of airborne sound.

Impact Insulation Class (IIC)

A single-number rating for comparing attenuation of impact sounds, such as footsteps, in floor-ceiling assemblies.


A measure of the total sound absorption provided by an object or surface.  Sound absorption performance of non-continuous sound absorbers, such as baffles, canopies, and clouds, are typically expressed in terms of sabins.


The persistence of sound in an enclosed space due to repeated reflections of sound waves.  Excessive reverberation can result in noisy environments with poor speech intelligibility.

Speech Intelligibility

 A measure of comprehensibility of speech within the set room conditions.  Speech intelligibility is influenced by a number of factors, including reverberation and background noise. 

Speech Privacy

The opposite of speech intelligibility, speech privacy is the inability to understand conversations by an outside listener.  Speech privacy in enclosed spaces is primarily influenced by the sound transmission properties of the walls, floor, and ceiling construction, as well as background noise. 

Background Noise

Also known as ambient noise, background noise is any sound other than the primary sound being conveyed, such as speech.  Background noise can either reduce speech intelligibility or enhance speech privacy.

Additional information on key terms in acoustics can be found here.