Page 248 - Master Handbook of Acoustics
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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.