Method for evaluation of the acoustical impedance of a black box, with or without mean flow, measuring pressures at fixed positions

Kathuriya, ML and Munjal, ML (1977) Method for evaluation of the acoustical impedance of a black box, with or without mean flow, measuring pressures at fixed positions. In: Journal of the Acoustical Society of America, 62 (3). pp. 755-759.

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Abstract

The transmission-line or the impedance-tube method for the measurement of the acoustic impedance of any termination involves a search for various minima and maxima of pressure. For this purpose, arrangement has to be made for the microphone to travel along the length of the impedance tube, and this complicates the design of the tube considerably. The present paper discusses a method which consists in evaluating the tube attenuation factor at any convenient frequency by making use of measured SPL's at two (or more) fixed locations with a rigid termination, calculating the tube attenuation factor and wave number at the required frequency of interest with or without mean flow (as applicable), and finally evaluating the impedance of the given termination by measuring and using SPL's at three (or more) fixed locations. Thus, the required impedance tube is considerably smaller in length, simpler in design, easier to manufacture, cheaper in cost and more convenient to use. The design of the tube is also discussed. Incidentally, it is also possible to evaluate the impedance at any low frequency without having to use a larger impedance tube.

Item Type:	Journal Article
Publication:	Journal of the Acoustical Society of America
Publisher:	American Institute of Physics
Additional Information:	Copyright of this article belongs to American Institute of Physics.
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	05 Feb 2010 06:40
Last Modified:	19 Sep 2010 05:50
URI:	http://eprints.iisc.ac.in/id/eprint/24401

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