Acoustical Glossary

The scientific study of sound, its production, transmission, and effects.

The properties of a material to absorb or reflect sound (adjective), Acoustically (adverb).

A review of a space to determine the level of reverberation or reflected sound in the space (in seconds) influenced by the building materials used to construct the space. Also the amount of acoustical absorption required to reduce reverberation and noise.

A professional who is experienced in providing advice on acoustical requirements, and noise control in a variety of situations.

The acoustical characteristics of a space or room influenced by the amount of acoustical absorption, or lack of it in the space.

Sound that reaches the point of interest by traveling through the air.

All noise level present in a given environment, usually being a composite of sounds from many sources far and near. Traffic, HVAC, masking sound or even low-level background music can contribute to ambient level of noise or sound.

The nonnegative scaler measurement of a sound wave’s peak magnitude during a frequency cycle or peak pressure variation.

The control of noise in a building space to adequately support the communications function within the space and its effect on the occupants. The qualities of the building materials used to determine its character with respect to distinct hearing.

A measure of rating building elements such as acoustical ceilings and acoustical screens for speech privacy purposes. AC values increase with increasing privacy. AC has replaced Noise Isolation Class (NIC) as the accepted industry standard performance value. NIC is based on hearing sensitivity rather than discernment of actual speech, which is the primary concern in open office layouts prevalent in acoustical design work.

A measure of speech intelligibility influenced by an acoustical environment, and rated from 0.01 to 1.00. The higher the number, the higher the intelligibility of the spoken word in a sentence from 0 to 100%.

Acoustical materials spaced apart can have greater absorption than the same amount of materials butted together. The increase in efficiency is due to absorption is due to more surface area on an acoustical panel, diffraction around the panels, and air space.

Acronym for American Society of Testing and Materials

A measure of sound pressure level designed to reflect the response of the human ear, which does not respond equally to all frequencies. To describe sound in a manner representative of the human ear’s response it is necessary to reduce the effects of the low and high frequencies with respect to medium frequencies. The resultant sound level is said to be A-weighted, and the units are in decibels (dBA). The A-weighted sound level is also called the noise level.

The sound level measured with a sound level meter using A-weighting, which alters the sensitivity of the sound level meter with respect to frequency so that the sound level meter is less sensitive is less sensitive at frequencies where the ear is less sensitive; usually used in specifying permissible sound levels in buildings.

The sum total of all unwanted residual noise generated from all direct and reflected sound sources in a space that can represent an interface to, or interfere with good listening and speech intelligibility. (Hearing impaired persons are especially victimized by background noise)

An acoustical sound absorbing unit. Normally suspended vertically in a variety of patterns to introduce absorption into a space to reduce reverberation and noise levels.

Anything physical or an environment that interferes with communication or listening

An acoustic absorber or sound baffle used mainly in sound-recording studios and home theaters to absorb sound at low frequencies less that about 100 hertz (Hz). Bass traps, like all acoustically absorptive materials, function by turning sound energy within the room into minute amounts of heat through friction.

Low frequency reflections. In small rooms, acoustical panels with air space behind can better help control low frequency reflectivity.

In acoustical industry terms, an acoustical panel suspended in a horizontal position from a ceiling or roof structure. Similar to a baffle, but in a horizontal position.

The Cocktail Party effect describes the ability to focus one’s listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations. This effect reveals one of the surprising abilities of our auditory system, which allows us to communicate in a noisy place, such as a cocktail party.

The typically high frequency at which sound can pass directly through a partition due to the partition resonating at that same frequency. Speed of wave traveling through the material equals the speed if the sound (incident) wave in air.

Vibrational energy is dissipated and converted into small amounts of heat as a result of the extension and compression, or shearing of a damping layer. A viscoelastic damping compound between two stiff or rigid constraining layers such as drywall or plywood. This conversion of vibration to heat reduces the resonance of the stiff layers much like placing a hand on a drum head to stop it from resonating.

In acoustics, the cycle is the complete oscillation of a sound wave’s pressure above and below the atmospheric static pressure.

The number of oscillations (cycles) that occur in the time frame of one second. (See FREQUENCY). Low frequency sounds have fewer and longer cycles than high frequency sounds.

The process by which vibrations are converted into heat over time and distance.

A logarithmic unit used to express the difference or magnitude of the level or power of sound intensity. It is equal to ten times the common logarithm of the ratio of the two levels. [DECI + BEL] A whisper is about 20 dB, typical conversation is between 60 – 70 dB, and the threshold of pain for the human ear is around 120 dB. Decibels are not directly related to human ear sensitivity and doubling dB does not equate to a doubling in perceived loudness since it works as a curve. 10 dB is a typical doubling or halving of perceived volume. Note that being logarithmic values, they cannot be added.