MEASUREMENT OF ACOUSTIC CONSTANTS OF CLOTH

Abstract

In the present paper, the writer accentuate the existence of the acoustic surge impedance or its density as defined by the complex ratio of pressure and velocity waves of sound through cloth or similar materials when both intensities are expressed in plane vectors and that of common attenuation constant in complex numbers for each wave.
A technique to measure these two constants is offered. The method is to measure the motional impedance of a telephone receiver coupled with an acoustic tube while the latter contains a sample of cloth or similar materials to be tested, as a sound screen somewhere in the tube. For a given frepuency, three measuremenents under different conditions of the tube are necessary to determine the two acoustic constants of the sample material when the receiver constants are known.
To show the usefulness of these constants, from the data thus obtained for a woolen cloth, propagation velocity of sound, reflection and transmission coefficients of pressure and velocity waves are calculated. In addition, a steady acoustic field-pressure and velocity waves as wall as power relations-near a semi-infinite screen and that of finite thickness is also discussed with numerical values for the woolen cloth.