Noise Standards

Sound is transmitted through the air as a series of compression waves. The energy of the noise source causes air molecules to oscillate radially away from the source. This oscillation results in a train of high-pressure regions following one another, travelling at a speed of approximately 760 miles per hour in sea-level air.

Noise can be described in terms of its loudness and its pitch, or frequency. Loudness is measured in decibels (dB). The dB scale, shown in Table 4.4.1, is a logarithmic scale— a 20 dB sound is ten times louder than a 10 dB sound. Pitch is a measure of how high or low a sound is. Pitch is measured in cycles per second (cps), or hertz (Hz). This measurement is the number of compression waves passing a point each second. The human ear is sensitive to sounds in the range of 20 to 20,000 Hz, but the ear is not as sensitive to low- and high-frequency sounds as it is to medium-frequency sounds (Figure 4.4.1).

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