3 Acoustic Measurements

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Noise control programs often require measurements of various acoustic

quantities to determine the effectiveness of the noise control procedure.

There may be other reasons for the need of experimental data. Noise measurements

must be made to determine compliance with noise regulations.

Noise measurements may be needed for diagnostic purposes or to locate the

source (or sources) of noise in a piece of machinery. The transmission path

(or paths) for noise in a system may be identified through acoustic measurements.

It is important that the measuring equipment be properly selected to

monitor and measure sound properties. When we have a basic situation in

which we need to assess the severity of environmental noise, we may need to

measure only the overall sound pressure level or the A-weighted level, using

a simple sound level meter. For example, if we wish to determine if the

sound level in a room exceeds 90 dBA, then a portable or hand-held

sound level meter is the appropriate instrument to use.

There are cases where we require a more detailed analysis of the

noise. In these cases, octave band or 1/3 octave band sound level measurements

may be made. A sound level meter with octave band or 1/3 octave

band filters is required. An acoustic spectrum analyzer, in which microprocessors

are used to manipulate the input data, may be the instrument

of choice.

Copyright © 2003 Marcel Dekker, Inc.

For verification of compliance with noise exposure regulations, dosimeters

may be used to measure and record cumulative noise exposure.

Data on the sound power generated by machines and equipment may

be needed in the development of quieter mechanical systems, in making

acoustic comparisons of several different machines, and in the generation

of data on production machines and equipment. There is no ‘‘acoustic

wattmeter’’ available for direct measurement of acoustic power; however,

the techniques for sound power determination from sound pressure measurements

will be discussed in this chapter.

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