4.1 The sound absorption of a material that covers a flat surface depends not only on the physical properties of the material but also on the way in which the material is mounted over the surface. The mountings specified in these practices are intended to simulate in the laboratory conditions that exist in normal use.

4.2 Some of the specified mountings require special fixtures or minor deviations from normal practice. These fixtures or deviations are to be used only during laboratory tests and should not be specified for practical installations. They are noted in the specifications for the mountings in question by the phrase "for laboratory testing only."

4.3 Test reports may refer to these mountings by type designation instead of providing a detailed description of the mounting used.