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Noise Control Terms

A-Weighting – The filtering system in a sound meter that allows the meter to disregard lower frequency.

Absorption Coefficient – The ratio of the sound absorbed to the sound incident on the material or device.

Acoustical Analysis – A determination of the level of reverberation or reflected sound in the space for which the building materials are a factor. Acoustical analyses also determine how much acoustical absorption is needed to reduce reverberation and unwanted noise.

Acoustical Material – The material used to change a sound field by absorbing, damping or blocking acoustical energy.

Acoustics – The science of sound, which includes its creation, transmission and effects.
 
Airborne Noise – The uninterrupted transmission of noise into the atmosphere. Airborne noise can be controlled by absorption or by being blocked.

Ambient Noise – The sounds within a given environment from many different sources.

Anechoic Room – A test chamber lined with absorbent acoustical material used to eliminate sound reflections and to determine the sound radiation characteristics of equipment.
 
Bel – A unit of measurement referring to sound intensity. One bel equals 10 decibels.

Damping – The process of dissipating mechanical vibratory energy into heat. Damping materials are used to apply to vibrating surfaces in order to reduce the noise radiating from that surface.
 
Decay Rate – The rate at which sound will fade when the noise source is removed, expressed in dB/sec.
 
Decibel (dB) – A unit of measurement referring to sound intensity that is equal to one tenth of a Bel.

Dissipative Silencer – A device inserted into air ducts or openings that reduces the noise transmitted through the ducts or openings. Noise reduction is accomplished by using internal sound absorbing materials.
 
Flanking – The pathway along which sound travels around the perimeter or through holes within partitions or barriers erected to reduce the sound isolation between areas. Examples of flanking paths include ductwork, piping, back-to-back electrical boxes within partitions, window mullions, etc.
 
Free Field – Sound from an outdoor source where no obstructions exist.
 
Hearing Threshold Level (HTL) – Amount in decibels that a specified signal can exceed to cause damage to the ears of a listener.
 
Hertz (Hz) – Sound frequency expressed by cycles per second.

Insertion Loss – The reduction of sound power levels reached by inserting a muffler or silencer in an acoustic transmission system.
 
Live End/Dead End – An acoustical treatment plan for enclosed areas in which one end is highly absorbent while the other is reflective and diffusive.
 
Loudness – The strength of the physical resonance of a sound to sound pressure and intensity, as experienced by a listener.
 
Noise – A term referring to a sound of any kind, usually in reference to unintelligible or unwanted sound.
 
Noise Criteria (NC) – Sometimes referred to as “dBA levels,” it is used to assess listening conditions at ear level by gauging sound levels at loudest locations in a room.

Octave Band (OB) – A range of frequencies where the highest frequency of the band is double the lowest frefquency of the band.

Radiation – The process in which structure-borne vibrations are converted into airborne sound.
 
Reverberation – Sound waves that continue to bounce off surfaces after the source ends, until the sound waves lose energy and eventually die out.

Reverberation Room – A test chamber designed so that the reverberant sound field within the room has an intensity that should be the same in every direction and at every point. It is often used to measure transmission loss and sound absorption.

Sabin – The unit of measure used for sound absorption consisting of the number of square feet of sound absorbing material multiplied by the material absorption coefficient.
 
Septum – A thin layer of material sandwiched between two layers of absorptive material that prevents sound waves from passing through the absorptive material.

Sound – Pressure waves traveling through the air or in other elastic materials.

Sound Absorption – The acoustical process in which sound energy is dispelled as heat rather than reflected back to the environment as sound.

Sound Level Meter – An instrument used to measure sound pressure levels. Type 1 are precision instruments, whereas Type 2 are general purpose instruments.

Sound Power Level (Lw) – A measure of the total airborne acoustic power created by any noise source; it is expressed on a decibel scale referenced to a usual standard of 10-12 watts.

Sound Pressure Level (Lp) – A measure of air pressure changes caused by a sound wave and expressed on a decibel scale referenced to 20µPa.
 
Soundproofing – Creating an area insulated against noise.
 
Structure Borne Noise – The transmission of energy from vibrating structures or solids into noise.
 
Vibrations – Like those with structure borne noise, they are the wavering of a boundary that defines the motion of a mechanical system and can be reduced by isolators or damping.
 
Volume – Cubic area of a space calculated by the length x width x height of the space. Volume influences reverberation time.
 
Wavelength – Wavelike compressions and rarefaction produced by sound passing through air. Sound waves vary with frequency.