Page 248 - Master Handbook of Acoustics
P. 248

short-duration pulse, the time gate can be opened only for the desired sound pulse, shutting out the
  interfering pulses. This tone-burst method can be used to measure the sound-absorption coefficient of
  a material at any desired angle of incidence.

      Such an arrangement is illustrated in principle in Fig. 12-5. The source-microphone system is
  calibrated at distance x, as shown in Fig. 12-5A. The geometry of Fig. 12-5B is then arranged so that
  the total path of the pulse reflected from the material to be tested is equal to this same distance x. The
  strength of the reflected pulse is then compared to that of the unreflected pulse at distance x to
  determine the absorption coefficient of the sample.













































   FIGURE 12-5   Determining the absorption coefficients of materials by a tone-burst method. (A) The
   source-microphone system is calibrated at distance x. (B) The total path length of the pulse reflected
   from the material under test is equal to distance x.






  Mounting of Absorbents

  The method of mounting the test sample on the reverberation chamber floor is intended to mimic the
  way the material is used in practice. Table 12-1 lists the standard mountings, both in the ASTM form
  and in the older ABPMA form.
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