A Survey of Methods for Determining the Bulk Properties of Sound Absorbing Materials

摘要

This paper compares several approaches to determine the bulk properties (complex wavenumberand characteristic impedance) for sound absorbing materials. Acoustic bulk properties can bemeasured directly with an impedance tube using either the two-load, two-cavity, or threemicrophonemethod. In the absence of an impedance tube, flow resistance can be measured usingASTM C522. Once flow resistance is known, empirical models by Mechel (or Delaney andBazley) for fibers or Wu for plastic foams can be used. Alternatively, the sound absorption in animpedance tube can be measured and then the flow resistivity or Biot parameters, which providethe best fit to the measured absorption, can be determined. Each of the aforementioned methodsis compared for melamine foam and glass fiber, and advantages and disadvantages of eachapproach are discussed.