An acoustics glossary for architects and contractors

Construction documents always have technical acoustic terms all over! They might seem foreign but they are not hard to understand.

We have tabulated a glossary of terms commonly queried by architects and contractors. This glossary explains each term with practical situations so that they are more relatable.

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Acoustics Glossary

Prolongation of sound due to sound reflections.

What is heard: muddied, unintelligible sounds that are indistinguishable from sound source.

Reflection of sound that is heard more than 0.1s after direct sound is produced.

What is heard: reflected sound arriving at the listener with a distinguishable lag time.

The amount of time sound takes to decay by 60dB.

What this means: RT60 is an acoustical measurement of any space. The greater the RT60, the more reverberant a space sounds, vice versa.

Design consideration: Different spaces have different optimum RT60 suitable for its use. For example, a conference room would do well with a low RT60 while a symphony hall would do well with a higher RT60.

The range of frequencies absorbed by acoustic panels. Porous materials generally have broadband absorption while resonating panels generally have narrower absorption bandwidth.

What this means: Porous materials such as rockwool/fibreglass absorb a wide range of frequencies; resonating panels such as perforated/grooved panels absorb a narrower range of frequencies.

Design considerations: For most spaces (e.g. office, conference rooms), broadband absorption is sufficient to resolve reverberation issues. Acoustic panels using porous materials (e.g. Fabrix) can be used in these cases.

Measurement, between 0 and 1, of amount of sound energy absorbed by a material at specific frequencies. SAC 0 indicates total reflection while SAC 1 indicates total absorption.

Representation, between 0 and 1, of amount of sound energy absorbed by a material. NRC 0 indicates total reflection while NRC 1 indicates total absorption. It is the average of SAC values across different frequencies.

What this means: Two materials of the same NRC might not have the same performance as they can have different SAC values.

Sound transmission through the air.

Sound transmission through connected structures.

Rating of how effective a partition attenuates airborne sound.

What this means: STC measures/rates how well a partition stops transmission of airborne sound. This is a laboratory-derived rating.

The on-site measurement of STC is FSTC, but it is less often used as a post-construction test because it ignores sound transmission through flanking paths.

ASTC reflects the apparent performance of a partition, taking into consideration both airborne sound transmission and flanking paths. It is more commonly used as a post-construction test.

Rating for noise level within a space.

Rating of how effective a partition attenuates impact sounds.

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