LM3875 datasheet(18/20 Pages) NSC

18 / 20 page

Definition of Terms (Continued)

is also an excellent equation to determine the 3 dB point of a

closed-loop gain, assuming that you know the GBWP of the

device. Refer to the diagram below.

Bi-amplification: The technique of splitting the audio fre-

quency spectrum into two sections and using individual

power amplifiers to drive a separate woofer and tweeter.

Crossover frequencies for the amplifiers usually vary be-

tween 500 Hz and 1600 Hz. “Biamping” has the advantages

of allowing smaller power amps to produce a given sound

pressure level and reducing distortion effects produced by

overdrive in one part of the frequency spectrum affecting the

other part.

C.C.I.R./A.R.M.:

Literally: International

Radio

Consultative

Committee

Average Responding Meter

This refers to a weighted noise measurement for a Dolby B

type noise reduction system. A filter characteristic is used

that gives a closer correlation of the measurement with the

subjective annoyance of noise to the ear. Measurements

made with this filter cannot necessarily be related to un-

weighted noise measurements by some fixed conversion

factor since the answers obtained will depend on the spec-

trum of the noise source.

S.P.L.: Sound Pressure Level — usually measured with a

microphone/meter combination calibrated to a pressure level

of 0.0002 µBars (approximately the threshold hearing level).

S.P.L. = 20 Log 10P/0.0002 dB

Where P is the R.M.S sound pressure in microbars. (1 Bar =

1 atmosphere = 14.5 lb./in

2 = 194 dB S.P.L.).

01144914

FIGURE 3.

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