From The Master Handbook of Acoustics, Fourth Edition
Mounting of Absorbents
The method of mounting the test sample on the reverberation chamber floor is intended to mimic the way the material is actually used in practice. Table 9-1 lists the standard mountings, both in the old form and in the ASTM form that will be used in the future.
| New mounting designation [*] | Old mounting designation [**] | |
|---|---|---|
| A | Material directly on hard surface | #4 |
| B | Material cemented to plasterboard | #1 |
| C-20 | Material with perforated, expanded or other open facing furred out 20 mm (3/4 ?) | #5 |
| C-40 | Ditto, furred out 40 mm (1 1/2 ?) | #8 |
| D-20 | Material furred out 20 mm (3/4 ?) | #2 |
| E-405 | Material spaced 405 mm (16 ?) from hard surface | #7 |
| [*]ASTM designation: E 795-83. [**]Mountings formerly listed by Acoustical and Board Products Manufacturers Association, ABPMA (formerly the Acoustical and Insulating Materials Association, AIMA). The cooperation of Riverbank Acoustical Laboratory in providing information on current practice is gratefully acknowledged. |
The mounting has a major effect on the absorption characteristics of the material. For example, the absorption of porous materials is much greater with an airspace between the material and the wall. Tables of absorption coefficients should always identify the standard mounting or include a description of the way the material was mounted during the measurements, or the coefficients are of little value. Mounting A with no air space between the sound absorbing material and the wall...
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