Sound transmission loss as defined in Terminology C 634, refers to the response of specimens exposed to a diffuse incident sound field, and this is the test condition approached by this laboratory test method. The test results are therefore most directly relevant to the performance of similar specimens exposed to similar sound fields. They provide, however, a useful general measure of performance for the variety of sound fields to which a partition or element may typically be exposed.

In laboratories designed to satisfy the requirements of this test method, the intent is that only significant path for sound transmission between the rooms is through the test specimen. This is not generally the case in buildings where there are often many other paths for sounds-flanking sound transmission. Consequently sound ratings obtained using this test method do not relate directly to sound isolation in buildings; they represent an upper limit to what would be measured in a field test.

This test method is not intended for field tests. Field tests shall be performed according to Test Method E 336.

Note 2-The comparable quantity measured using Test Method E 336 is called the apparent sound transmission loss because of the presence of flanking sound transmission.