Industrial Acoustic Terms and Abbreviations Glossary

Our expertise in industrial acoustic and noise control solutions means that we sometimes use jargon. While that makes it efficient to describe our projects, sometimes that leaves our customers in the dark. Here’s a glossary of common industrial acoustic terms (and abbreviations) to help you better understand your project.

Acoustic Lagging

Materials applied externally to the surface of pipes and ducts to reduce radiated noise to the environment.

Acoustical Enclosure

A metal structure built around a turbine or machinery to reduce noise emitted to the environment.

Airborne Sound

Sound or noise radiated directly from a source, such as a turbine or machine, into the surrounding environment.

Ambient Noise

Total noise level in a specified environment.

Attenuation

Term used to indicate the general noise reduction of acoustic panels, silencers, enclosures, etc., usually expressed in decibels.

Audible Frequency Range

Normal hearing for a healthy person ranging from approximately 20 Hz to 20,000 Hz (20 kHz).

A-weighting

A frequency weighting adjustment that conforms approximately to the response of the human ear.

Background Noise Level

Prevailing noise level in a specified environment measured in the absence of the noise being studied.

Continuous Equivalent Noise Level, Leq, LAeq

Steady noise level (usually in dBA) which, over a specified period of time, contains the same amount of sound energy as the time varying noise.

dB (A)

The A-weighted sound pressure level, in decibels.

Decibel (dB)

Degree of loudness. A unit for expressing the relative intensity of noise on a scale from 0 dB for the least perceptible sound to 130 dB for a level so loud it causes pain (referred to as “threshold of pain”).

Directivity Index (DI)

The difference between sound pressure level in any direction in the acoustic far-field and the average sound pressure level in that field. For example, noise emanating from a stack exit will vary with directivity angle between the point of measurement and the center line.

Far-Field

Part of the sound field where the sound wave is spreading spherically. Sound decays at 6 dB for a doubling of the distance from the sound source.

Free-Field

An environment where there are no reflective surfaces.

Frequency

Number of cycles or pressure variations per second. Expressed in Hertz (Hz).

Full (1/1) Octave Bands

Sound levels are normally reported in ten (10) full octave bands which cover the audible frequencies from 20 to 16,000 Hz. Each octave band is denoted by a center frequency (OBCF) as follows; 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 8000 Hz, 16000 Hz.

Insertion Loss (IL)

The difference, in dB, between two sound pressure levels (or sound power levels) which are measured at the same point in space before and after a silencer is inserted between the measurement point and the noise source.

Near-Field

Area that surrounds the noise source. Sound does not decay at 6 dB for a doubling of the distance from the sound source.

Noise

Pressure fluctuations in air that the human ear can hear.

Self-Noise

Sound level, denoted in dB, generated within a silencer caused by air flow over the internals of the silencer. Self-noise reduces the effectiveness of the silencer.

Sound Pressure

Pressure fluctuations in air, measured in Pascals (Pa). Audible sound pressure variations are very small, ranging from about 20 μPa (2×10−5 Pa) to 100 Pa.

Sound Pressure Level, Lp (SPL)

Sound pressure measured on a decibel scale.

Sound Transmission

The transfer of sound energy through a barrier from one medium to another.

Structure-Borne Noise

Generation and propagation of time-dependent motions and forces in solid materials, which result in unwanted, radiated sound.

Transmission Loss

The difference, in dB, of the sound power incident on a structure to the sound power transmitted by that structure. Describes the ability of a solid surface to block the propagation of noise.

Wavelength (λ)

Length of cycle, calculated by dividing speed of sound in air by frequency (λ = c/f, where c = speed of sound, 343 m/s standard day).

Do you need help with custom-engineered industrial noise control solutions? SVI Dynamics offers industrial noise control modeling, planning, noise surveys, silencer inspections and plant and/or equipment noise control design support. Contact the engineers at SVI Dynamics today.