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

B-weighting

### Backward Curve Integration

, a method for calculating reverberation time from the impulse noise decay curve, also known as the Schroeder Method.

**EDT (early decay time)**, based on the impulse decay curve, 0 dB to -10 dB

**T10 decay time**, based on the impulse decay curve, -5 dB to -15 dB

**T20 decay time**, based on the impulse decay curve, -5 dB to -25 dB

**T30 decay time**, based on the impulse decay curve, -5 dB to -35 dB

### Balanced Noise Criteria (NCB)

, a refinement of the noise criteria rating system. The rating is determined by the speech interference level, resulting in the following classifications.

*R is for Rumble*, if the spectrum is rich in low frequency sound.

*H is for Hiss*, if the spectrum is rich in high frequency sound.

*RV is for Rattle and Vibration*, if the low frequency spectra is likely to produce audible rattling in lightweight building elements.

*Balance noise criteria* also includes the 16 and 31.5 Hz octave bands

See also • noise rating (NR) curves and room criteria (RC)

**Band**, a continuous range of frequencies between two limiting frequencies.

### Band Pass 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.

See also octave bands and third octave bands

**Bar**, the 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 sound or vibration components are quite close together in frequency and are present at the same time at the same place, they will combine in such a way that their sum will vary in level 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.

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.

The decibel is used extensively in acoustics, so we have a more detailed description.

Bending Wave

**Binaural**, hearing involving both ears

### Binaural Recording

uses 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, so the

*bow tie correction* compensates for this.

**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.

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