If the sound power of a source is obtained by forming the surface integral of the normal component of the sound intensity vector, the shape of the surface of measurement is unimportant and projection error only occurs as a result of nonideal polar response of the composite microphone. Furthermore, the sound power of the source may be determined selectively in the presence of background noise originating outside the closed surface. If a sufficient number of points of measurement are taken, the error depends mainly on the signal−to−noise ratio at each point and on the accuracy of the measuring system.
Subject Classification: 50.25, 50.85.
Two portable, battery-powered, transistorized meters have been designed to produce direct measurements for the prediction of subjective response to noise. One of these meters reads loudness (octave-band sones and total sones) and loudness level (phons) based on Steven's method. The other meter reads Speech Interference Level in decibels (re 0.0002 microbar) based on the average sound pressure level of the three octave-bands from 600 to 4800 cps. These direct reading meters are utilized to replace the sound level meter-octave band analyzer combinations customarily used for these applications. The construction and the applications of the meters are discussed.
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