Abstract
A simple correlation technique is presented for measuring acoustic absorption coefficients and impedances of surfaces for sound incident at any angle. The measurements can be made in situ; the technique is useful for measuring ground impedance and the surface impedance of buildings, as well as the impedance of acoustic absorbing material. The technique uses a simple source and one microphone, both placed a few acoustic wave-lengths away from the surface. The source signal is random noise, and the microphone output is filtered through a narrow frequency band with a suitably smooth filter shape. Values of the absorption coefficient and impedance at any frequency are obtained from the autocorrelation curve of this narrowband signal. [Work supported by NSF.]
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