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 the 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 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 playing 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.
Sound Masking	Any means of reducing or eliminating sound pressure with respect to a specified source and receptor.