Sound Power Measurements in Air in the Near Field of Sound Sources Using the Sound Intensity Method.

Abstract : Sound power is the acoustic energy output in watts of a sound-producing source. Sound power can be determined with an array of pressure sensing transducers placed around a source in an anechoic chamber, as specified in standard 3744-1981 (E). In contrast, sound intensity can be used to measure sound power by measuring the intensity output of the source in watts/sq. m. over a closed surface and using the definition of sound power (intensity X area) to find sound power. Advantages of the sound intensity method are that one measuring probe is used, which consists of two closely placed pressure sensing transducers: no anechoic chamber is needed; measurements can be done in the near field; and background noise can be present. Disadvantages are that: no standards exist yet; and the phase response between the two transducers in the probe must match closely, either through quality transducers or by careful calibration. The two methods of determining sound power were systematically compared. Tests showed that the sound power results from the sound intensity method, even in fairly adverse environments, were comparable to results obtained using the ISO method in most situations.