The Book of Acoustics

10.0 Glossary of Acoustic Terms

10.0 Glossary of Acoustic Terms


When a sound wave encounters a surface and the energy is absorbed by the surface rather than reflected.

Absorption coefficient

A measurement used to evaluate the sound absorption efficiency of materials.


The science of sound; a branch of physics dealing with mechanical waves.


Increasing the volume of sound.


Sound, transmitted in the form of signals.

Auditory system

The body system responsible for the sense of hearing.


Related to the sense of hearing.


The modelling and simulation of acoustic phenomena rendered as a soundfield in a virtualized space.


Free from echoes.


A measure of the width of a range of frequencies, measured in Hertz.


Relating to hearing involving two ears. Human hearing is binaural, which allows the listener to determine the direction and origin of sound.


Sound blocking is the introduction of barriers that prevent the travel of sound waves from one space to another.


An acoustic treatment by which noise is masked by another layer of sound, such as a water feature in a public space or pre-recorded music played on a speaker system.


Used variably to describe either absorption, diffusion and/or blocking of sound to achieve a more quiet and less resonant acoustic environment.

Decibel (dB)

A standard unit used to measure the intensity of sound.


The degree to which a material is compact, which can affect the extent to which it allows sound to pass through it.


The bending of sound waves around obstacles and the spreading out of sound waves beyond openings.


The spreading out of sound waves to achieve a more “even” acoustic environment.


Where a sound wave separates into its component frequencies as it passes through a material.


The sound caused by the reflection of sound waves, which arrives at the listener later than the original sound.

Environmental noise

The accumulation of noise pollution that occurs outside.

Frequency (Hz)

The speed of vibration which determines the pitch of a sound, measured in Hertz.


A measure of how comprehensible speech is in given conditions.


A phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude.


The subjective perception of sound pressure.

Mechanical wave

A wave that is an oscillation of matter, and therefore transfers energy through a medium. Sound waves are a type of mechanical wave.


Sound, particularly that which is loud, unpleasant or causes disturbance.

Noise Rating curve

A standard determining the acceptable level of sound in an interior environment for hearing preservation and verbal communication.

Noise reduction coefficient (NRC)

A representation of the amount of sound energy absorbed upon striking a particular surface, measured on scale between 0 and 1 where NRC 0 = complete reflection and NRC 1 = complete absorption.


Repeatedly and regularly fluctuating above and below a mean value. Sound oscillates as it travels, hence the wave pattern.


Occupational Safety and Health Administration, the body responsible for setting the acceptable limit of noise exposure for workers in the USA.


The study of the psychological and physiological effects of sound on human beings.

Room absorption

The sum of Sabine absorption due to objects and surfaces in a room.


When a sound wave hits a surface, it reflects, either in a relatively straight line or in scattered pattern, depending on the texture and density of the surface.


Acoustic refraction, in which the path of sound waves is redirected, occurs when sound waves enter a medium in which their speed changes. The temperature of the air, for instance, can cause sound waves to be refracted.


The reinforcement or prolongation of sound by reflection from a surface, or by the synchronous vibration of a neighbouring object.


A device or system that exhibits resonance or resonant behaviour.


The persistence of sound after the sound is produced. Created when a sound is reflected, causing numerous reflections to build up then decay as the sound is absorbed by surrounding surfaces and objects.

Reverberation time

The lifetime or persistence of a sound wave in an enclosed space.

Room acoustics

A broad term representing how sound behaves in an enclosed environment.


Unit of sound absorption, named after Wallace Clement Sabine, founder of the field of architectural acoustics.

Sabine formula

Formula developed by Wallace Clement Sabine that allows designers to plan reverberation time in a space prior to construction and occupancy.

Sound absorption class

A set of internationally recognised sound classes for materials, ranked from A to E. A higher ranking sound class (A) is not necessarily better, depending on the needs of the project.

Sound absorption coefficient

Alternative name for the Noise Reduction Coefficient (NRC) described above.

Sound wave

Longitudinal wave consisting of areas of high and low air pressure.


A sound or combination of sounds


To reduce or eliminate the transfer of sound from one area to another.


The movement of sound through and between materials.


Sound waves with frequencies above the human hearing capacity, often used in medicine.

Wood wool 

A common material in acoustic design, made of processed timber, that absorbs sound when installed on interior surfaces.


The Book of Acoustics

This is a handbook for architects and interior designers who want to create acoustically beautiful spaces that make people feel happier, healthier and more productive.