Analysis Methods for Acoustical Systems Based on the FFT and Intensity Techniques

摘要

A two-part study on the measurement and analysis of acoustical systems is presented, consisting of the development of various new methods based on the FFT and intensity, and a collection of experiments for testing their applicability. The common factor in the studies is the FFT: the measurements were made with a dual-channel FFT analyzer, and the 2-D space-wavenumber FFT is used in some subsequent analyses. Most of the methods and experiments are further related to the two-transducer sound intensity techniques either directly or via some extension. In the method development part, the main theme is the direct measurement of acoustic impedance with the intensity technique. This is followed by additional developments for the determination of the incident power of an arbitrary sound field, the radiation efficiency, absorption coefficient and transmission loss. Two versions of the incident power method were formulated, one employs direct calculation of the Rayleigh integral in the space domain, and the other uses holographic approach in the wavenumber domain. In the experimental part, a number of simple acoustical systems are analyzed using the new developed methods and, whenever possible, other well known methods for comparison purposes. The investigated systems include a wool absorbent, grass-covered ground surface, a loudspeaker, a two-pane window, a wind tunnel, and a simple model silencer.