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A Novel Single-Microphone Method of Measuring Acoustical Impedance in a Tube

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A method is presented, for measuring acoustical properties of materials, which the authors believe to be novel and unique. The method relies on an MLS (maximum length sequence) excitation signal to measure the acoustical impedance of a specimen of material placed at the termination of a long tube. Whereas the traditional methods require that measurements be made at multiple locations within the tube, either using a multi-channel data acquisition system, or by physically moving a single microphone from one location to the next, the novel method requires only a single measurement at one location in the tube, using a single microphone. The necessity to conduct only a single measurement makes this method two to four times faster than traditional methods, depending on the desired frequency range of the measurement. Other benefits of this method include the fact that it requires only a single channel data acquisition system and single microphone, and that it has the unique ability to measure the impedance of the source end of the tube (i.e., the loudspeaker) as well as the material specimen at the termination end of the tube.

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AES - Audio Engineering Society