## B : Sound and Vibration Definitions, Terms, Units, Measurements ...

B-weighting

the noise at a given location and time, measured in the absence of any alleged noise nuisance sources, also known as Residual Noise.

**Background Noise Definition** IEC 801-21-13, total of interference from all sources in a system used for the production, transmission, detection, measurement, or recording of a signal

LA90, the noise level just exceeded for 90% of the time, is often used to measure *background noise* as recommended in BS 4142 - see also statistical noise levels.

We have a full page on Background Noise

Other noise descriptors :
ambient noise •
broadband noise •
narrowband noise •
periodic •
pink noise •
pseudo random noise •
random noise •
specific noise •
white noise •
wideband noise

### 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.

See also noise criteria

### Band

a continuous range of frequencies between two limiting frequencies.

See also octave •
one-third 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

range of frequencies, usually of standard size in acoustics, for example octave or one-third 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 kilopascal 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.

phenomenon that results from the linear or non-linear superposition of two or more waves of the same kind but of different frequencies.

### 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

a bel is equal to 10 decibels (dB) and because it is a ratio of two quantities it is dimensionless.

The decibel (dB) is used extensively to 'describe' acoustic levels.

unit of level of a quantity proportional to power when the base of the logarithm is ten. Also, the unit of level of a field quantity when the base of the logarithm is the square root of ten

● Note 1 examples of power-like quantities are sound power and sound energy.

● Note 2 examples of field quantities are sound pressure and voltage.

Bending Wave

**Binaural** hearing involving both ears

### Binaural Recording

sound recorded using two microphones spaced to simulate the listeners ears and usually transmitted separately to each ear of the listener. The results, using good quality headphones, can be very realistic.

See also localisation and our head and torso simulator - HATS

Boundary Effect

### Bow-tie Correction

multispectral 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 narrowband noise.

Other noise descriptors :
ambient noise •
background noise •
broadband noise •
narrowband noise •
periodic •
pink noise •
pseudo random noise •
random noise •
specific noise •
white noise •
wideband noise

See also
constant bandwidth •
constant percentage bandwidths •
octave bands •
FFT- fast fourier transform

**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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