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The Decor Systems Acoustics Glossary

Published30 May 2021
Written ByRebecca Fox

We've compiled the key terminology when it comes to all things acoustics. Bookmark this page for easy access to the information you need.

Absorption Coefficient (alpha)

The dimensionless ration of absorbed to incident sound energy from a single interaction between a sound wave and a partition. Values range from 0 to 1.


The product of absorption coefficient and surface area of a material, in units of sabins, is used to designate the amount of sound absorbed by that material. The properties of a material composition convert sound energy into heat thereby reducing the amount of energy that can be reflected.


The sound characteristics of a room. The science of the production, control, transmission, reception and effects of sound and the phenomenon of hearing.

Acoustic Material Selection

It is a given that soft furnishings typically diminish reflections and lessen the reverberation time whilst hard surfaces such as concrete, glazing, and plasterboard will usually raise reverberation time.

The use of glazing, concrete and plasterboard need to be complemented with a careful selection of complementary acoustic panel systems to ensure adequate acoustic control.

It is well-known that perforated, slotted and slatted acoustic panel systems can be appropriately engineered to absorb noise. The layout, substrate, finish and perforation pattern can be configurated to meet both acoustic and aesthetic requirements.

Industry experts such as interior designers and architects should seek an acoustic consultant to assist with the support of acoustical design within any functional space. Your Decor Systems consultant will be happy to assist you in this.

Ambient noise

All pervasive noise that's associated with a given environment.


The reduction of sound energy as a function of distance travelled.

Ceiling Attenuation Class (CAC)

CAC refers to the Ceiling Attenuation Class (CAC) value which is a rating that describes a materials ability to prevent sound from travelling between partitions through the ceiling cavity. It is usually required between private spaces when the walls do not go full height.


The loss of energy in a vibration system, usually through friction.

Decibel (dB)

A unit of sound level implying 10 multiplied by a logarithmic ratio of power or some quantity proportional to power. The logarithm is to the base 10. Sound intensity is described in decibels. For example breathing, 5 dB; office activity 50 dB; jet aircraft during take-off at 300′ distance, 130 dB.


The scattering or random distribution of a sound wave after striking a surface.


A repetitive echo set up by parallel reflecting surfaces.

Frequency (f)

The number of oscillations or cycles per unit of time. Acoustical frequency is usually expressed in units of Hertz (Hz) where one Hz is equal to one cycle per second. Interpreted subjectively as pitch. Humans can hear sounds having frequencies between 20 and 20,000 Hz.

Hertz (Hz)

Frequency of sound expressed by cycles per second.


Resistance to the transmission of sound by materials and structures. The separation of airborne or mechanically transmitted energy.

Noise Reduction Coefficient (NRC)

A single number rating system for absorption coefficients over the speech frequency range. The NRC of an acoustical material is the mathematical average to the absorption coefficients at 250, 500, 1000, 2000 Hz.


The perceived auditory sensation of sounds is expressed in terms of the high or low-frequency stimulus of the sound.


This is the portion of a sound wave that is not absorbed when meeting an object. The portion of the sound wave will change direction and continue to travel. 100% reflection is represented as “0” on the sound absorption coefficient rating. It is the opposite of absorption.

Reverberation Time

Reverberation is the accumulation of soundwaves in a space. Because reverberated sounds stack up, they can make direct communication difficult because there is so much ambient sound, and the direct sound can get lost.

When that happens, people tend to speak up to be heard over the din which only causes more reverb, and the cycle continues.

Reverberation time is the time (in seconds) taken for the sound pressure level generated by a source to decay by 60 decibels following the conclusion of the source event. It provides relevant information for assessing the speech intelligibility and the acoustic quality of a space. It is sometimes referred to as the “echo” in a room.

Both excessive and lack of reverberation can lead to a poor acoustic environment depending on the function of the space. This means that in order to achieve the correct range of reverberation time for a space – it must be calculated.


Rw refers to the weighted noise reduction that roughly corresponds to the decibel scale. It is a measure of how much airborne sound is attenuated between a partition. This is the descriptor that would usually be described as “Soundproofing”.

Sound absorption

This refers to the portion of a sound wave that is not reflected when meeting an object. This portion of the sound wave will not continue to travel and will be converted into thermal energy. 100% absorption is represented as “1” on the sound absorption coefficient rating. It is the opposite of reflection. Sound absorption reduces reverberation time.

Sound Absorption Coefficient (SAC)

The fraction of energy striking a material or object that is not reflected. For instance, if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient is 0.30. SAC = absorption / area in sabins per sq.

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