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AN ANALYTICAL INVESTIGATION OF THE INDIRECT MEASUREMENT METHOD OF ESTIMATING THE ACOUSTIC IMPEDANCE OF A TIME-VARYING SOURCE

✍ Scribed by K.S. PEAT; J.-G. IH

Publisher
Elsevier Science
Year
2001
Tongue
English
Weight
337 KB
Volume
244
Category
Article
ISSN
0022-460X

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✦ Synopsis

This paper presents an analytical investigation into the relationship between the characteristics of a linear, time-variant acoustic source, and the e!ective source impedance and source strength which follow if one then assumes the source to be time invariant. It thus models the indirect measurement method of obtaining the e!ective source characteristics of an actual time-varying acoustic source such as the intake or exhaust system of an internal combustion engine. It is shown that the e!ective source impedance and source strength have no physical meaning, bear no resemblance to the real source, and are dependent on the load system used to evaluate them. It is found that the e!ective source resistance is frequently negative; hence time variance of the source alone is a su$cient reason for the implausible negative resistance values as observed with the indirect measurement method. It is also shown that the meaningless e!ective source characteristics do, nevertheless, sometimes give a fairly accurate estimate of the noise output when the acoustic source is used with a di!erent load, again as observed by experimentation.

2001 Academic Press

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