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Chapter Twenty
Figure 20.1
Sound transmission.
20.3
Methods of Specifying
and Measuring Sound
There are several ways of describing the characteristics of sound:
sound power, sound pressure, intensity, loudness, frequency, speed,
and directivity.
20.3.1
Sound power
An acoustical source radiates energy in the form of sound. This acous-
tical power is expressed in watts. A
watts exponential
scale of sound
power has been developed. A sound power level of 10
⫺
12
W represents
the threshold of hearing for excellent young ears. This is given the
value of 0 dB (decibels) and is the reference level for Table 20.1. Table
20.1 lists the decibel value corresponding to a given watts exponential,
together with an example of this sound power, over a scale from 0 to
200 dB.
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