Acoustic Terms Glossary

Acoustic Terms Glossary

Sound Transmission Class(STC) – A single number rating for describing sound transmission loss of a wall or partition. A rating system designed to facilitate comparison of the sound transmission characteristics of various architectural materials and constructions. 

Noise Reduction Coefficient (NRC) – The arithmetic average of the Sound Absorption Coefficients of a material at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. This is the range having the most impact upon speech intelligibility.

Absorption – The opposite of reflection. Sound absorption results from the conversion of sound energy into another form, usually heat or motion, when passing through an acoustical medium. When a sound wave encounters resistance, absorption occurs. Absorption is measured in sabins. One sabin is the amount of absorption offered by one square foot of open air.  

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

Ambient noise – All pervasive noise associated with a given environment.

Attenuate – To reduce the level (volume, loudness, energy) of an acoustical (or electrical) signal.

Barrier – Heavy, dense and massive material used to block sound.

Bass Trap – A low frequency Sound absorber. Low frequencies are particularly difficult to absorb due to their long wavelengths. Bass traps are designed and constructed to absorb these longer waves and control unwanted room resonances. Broadband absorbent extending to lower frequencies are often called Bass Traps, imprecisely. The term “bass trap” is counter intuitive since these devices eliminate low frequency room cancellations, allowing bass to be heard.

Block – To reduce airborne sound transmission.

Echo – A distinctly discernible reflection, or repetition of a source signal. Note: The term is often used incorrectly to refer to reverberation which consists of densely spaced, indistinguishable reflections.

Reactive silencer – A silencer in air-conditioning systems that uses reflection effects for its action

Sound level – The intensity of sound measured with a sound level meter and one of its weighting networks.