Measurement of Normal Incidence Absorption Coefficient Using Sound Intensity.
Paper in Inter-noise 89 Inst Noise Control Eng Poughkeepsie NY :1077-1080
The accepted laboratory procedure for measuring the normal incidence absorption coefficient of materials depends on a determination of the standing wave pattern in an enclosed tube. This method has been relied on by the U.S. Bureau of Mines in its efforts to characterize the performance of acoustical materials that have been subjected to physical agents typically found in mining environments. However, the standing wave method is not ideally suited for this kind of measurement since the physical condition of a test sample saturated with either oil or water can change rapidly with time. Thus, with the standing wave method it is simply not possible to obtain absorption data for all frequencies at the same point in time. Due to the continuing research interest in the long-term performance of acoustical materials used in mining noise control, sound intensity has been investigated as an alternative approach to measuring the absorption coefficient. In general, it is concluded that the sound intensity technique promises a more convenient and efficient method for the measurement of normal incidence absorption coefficient. This will provide a tremendous advantage in those situations where it is critical to measure at all frequencies simultaneously.
Paper in Inter-noise 89; Inst. Noise Control Eng., Poughkeepsie, New York, PP. 1077-1080