Definitions, Terms, Units and Parameters

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Background Noise

: the noise at a given location and time, measured in the absence of any alleged noise nuisance sources, also known as residual noise. We also have a separate page on background noise

The LA90 - level exceeded for 90% of the measured time - is commonly used. see also statistical noise levels.

Backward Curve Integration

: method for calculating reverberation time from the impulse noise decay curve. Also known as the Schroeder method.

Balanced Noise Criteria

: is a refinement of NC Noise Criteria. The rating is determined by the SIL Speech Interference Level and gets the Classification (R) for Rumble if the spectrum is rich in low frequency sound, the Classification H for Hiss if the spectrum is rich in high frequency sound, or Classification (RV) for Rattle and Vibration and Rattle if the low frequency spectra is likely to produce audible rattling in lightweight building elements.

Band

: a continuous range of frequencies between two limiting frequencies. See also 1/1 octave and 1/3 octave

Band Pass Filter

: a filter covering a band of frequencies from a lower cut-off frequency to an upper cut-off frequency. Outside the filter bandwidth, the signal is attenuated.

Bandwidth : -3 dB

: range of frequencies usually in standard sizes i.e. octave or 1/3-octave bands. The lower and upper frequencies are also known as the -3 dB or half-power points - see also constant percentage bandwidth.

Bar

: unit of atmospheric pressure, equal to 1000 millibars, one million dynes per square centimetre, 100 kilopascals or 29.53 inches of mercury.

Bark

: the human ear combines sounds of similar frequency into frequency bands, called 'critical bands'. Dr Zwicker divided the audio spectrum into 24 critical bands and named the units 'barks'. See also loudness .

Beat Frequency

: if two vibration components are quite close together in frequency and if they are present at the same time at the same place, they will combine in such a way that their sum will vary in level up and down at a rate equal to the difference in frequency between the two components. This phenomenon is known as beating, and its frequency is the beat frequency.

Bel : B

: a logarithmic measure of sound levels relative to a reference or threshold level. In practice, sound levels are almost always stated in decibels. One bel is equal to 10 decibels, dB and because it is a ratio of two quantities it is dimensionless.

Bow-tie Correction

: multispectra measurements for correlation functions are performed using spectrum averaging. Half of the normal time record is set to zero. Accordingly, correlation functions for continuous signals will decrease with the delay. The bow-tie correction compensates for this.

Broadband Noise

: also called wideband noise - noise whose energy is distributed over a wide section of the audible range as opposed to narrow band noise, - other Noise Terms.

Buffer

: a memory location in a computer or digital instrument that is set aside for temporary storage of digital information while it is waiting to be processed.

Building Acoustics

: see - Flanking, Reverberation, Sound Insulation

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