A Sound Glossary

Absorption – the measure of energy removed from sound waves as they pass through a given thickness of material 

Absorption Coefficient – Used to evaluate the sound absorption efficiency of materials. It is expressed as the ratio of absorbed energy to incident energy

Acoustics – The properties or qualities of a room or building that determine how sound is transmitted in it

Acoustic Transmission – the transmission of sounds through materials, including air, walls, ceilings, and floors

Amplification – the process of increasing the volume of sound, especially using an amplifier

Bandwidth – A range of sound frequencies, measured in Hertz. The human ear can perceive approximately from 20 to 20,000Hz

Decibel (dB) – a unit used to measure the intensity of a sound

Density – the degree of compactness of a substance or material

Diffraction – the process by which a system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the waveforms produced

Diffusion – in architectural acoustics, is the spreading of sound energy evenly in a given environment. A perfectly diffusive space is one in which the reverberation time is the same at any listening position.

Echo – a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the listener. 

Frequency (Hz) – audio frequency is a periodic vibration whose frequency is in the band audible to the average human, measured in hertz (Hz). It is the property of sound that most determines pitch.

Intelligibility – a measure of how comprehensible speech is in given conditions. Intelligibility is affected by the level (loud but not too loud) and quality of the speech signal, the type and level of background noise, reverberation (some reflections but not too many), and, for speech over communication devices, the properties of the communication system.

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

Loudness – is the subjective perception of sound pressure. Perceived loudness consists of physical, physiological, and psychological components.

Noise – is unwanted sound considered unpleasant, loud, or disruptive to hearing

Noise reduction coefficient (NRC) – a single number value ranging from 0.0-1.0, where NRC 0 = complete reflection and NRC 1 = complete absorption, describing the average sound absorption performance of a material 

OSHA – Occupational Safety and Health Administration, a federal agency of the United States that regulates workplace safety and health and establishes the acceptable limit of noise exposure for workers

Psychoacoustics – the branch of psychophysics involving the scientific study of sound perception — how humans perceive various sounds. It is the branch of science studying the psychological responses associated with sound (including noise, speech, and music). Psychoacoustics is an interdisciplinary field of many areas, including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science.

Room absorption – refers to the process by which a room’s material, structure, occupants, and objects take in sound energy when sound waves are encountered, as opposed to reflecting the energy.

Reflection – the repetition of a sound resulting from reflection of the sound waves.

Refraction – of sound waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

Reverberation – is the persistence of sound after the sound is produced. A reverberation, or reverb, is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, surfaces, people, and air.

Sound Masking – 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.

Soundscape – A soundscape is an acoustic environment as perceived by humans, in context

Soundscaping – a term coined from acousticians who study soundscapes in nature. It describes the act of creating an experience of sound appropriate to the context of a space

Soundproofing – any means of reducing or eliminating sound pressure with respect to a specified sound source and receptor