5 Noise Sources

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When one carries out an acoustic design, it is often necessary to estimate the

sound pressure level that may be expected to be produced from a particular

noise source. If experimental data are not available for the noise source,

predictive relationships are needed. This situation arises when a new system

or installation is being developed. In addition, correlations for the noise

generated by a source, such as an item of machinery, provide information

for design which enables the designer to reduce the noise output from the

source by suitable modification of such factors as size, operational speed, etc.

In this chapter, we will examine methods that may be used to predict

the noise emitted from several mechanical systems. In general, it is important

to predict not only the overall noise level but also the noise spectrum or

the sound pressure level in each octave band. From a knowledge of the

sound pressure level spectrum (sound pressure level vs. octave band center

frequency), one may predict the A-weighted sound level, which is important

in determining compliance with noise regulations.

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