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Sound Power(W)
Sound Power Level (PWL, L
Sound Speed, (c,)
Spectrum (Frequency Spectrum) The amplitude of sound or vibration at various frequencies. It is
Threshold Sound Level (Lt)
Time Weighted Average Sound Level (TWA, L
Model 820 Technical Reference Manual
Weighted Peak: The peak value of a sound with a meter that has a
frequency weighting other than flat and a peak detector.
The sound power emitted by a sound source. It is measured in
Watts.
) The logarithmic form of sound power. It is also expressed by attach-
w
ment of the word decibel to the number. The logarithm is taken of
the ratio of the actual sound power to a reference sound power,
which is 1 pico-watt. Sound power level cannot be measured
directly, but can only be deduced through measurements of sound
intensity or sound pressure around the source. The equation for it is
L
The speed at which sound waves propagate. It is measured in
meters per second. It should not be confused with sound or particle
velocity which relates to the physical motion of the medium itself.
c
=
20.05 degC
c
=
given by a set of numbers that describe the amplitude at each fre-
quency or band of frequencies. It is often prefixed with a descriptor
that identifies it such as sound pressure spectrum. It is generally
expressed as a spectrum level.
The A-weighted sound level below which the sound produces little
or no Noise Dose accumulation and may be disregarded. It is used
for hearing damage risk assessment.
Standard: ANSI S1.25
TWA(TC)
Criterion Duration, that would expose a person to the same Noise
W
=
10log
------ -
w
10
W
0
+
273
49.03 degF
+
460
) It is the level of a constant sound over the
⁄
L
10
w
W
=
W
10
0
⁄
m sec
⁄
ft sec
C-17
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