The OILR and OITL produced by the methods described will not correspond to the transmission loss and noise reduction measured by Test Method E 90 and E 336 because of the different angular distributions that may exist in the outdoor incident sound fields (1)⁴ and the sound intensity distribution across the test facade. Of the three methods cited for measuring the outdoor sound field from a loudspeaker, the free and flush methods are more repeatable. The near method is used only when the free field and the flush methods are not feasible.

Flanking transmission or unusual field conditions could render the determination of OITL difficult or meaningless. Where the auxiliary tests described in Annex A1 cannot be satisfied, only the apparent OITL or the OILR are to be considered valid.

1.1 This guide covers field procedures for measuring the sound level reduction or sound transmission loss of an installed building facade or facade element in specified frequency bands. These values may be used separately to predict interior levels or combined into a single number such as by Classification E 413 (with precautions) or Classification E 1332 to estimate the sound insulating properties of the test element, FOITC, in the field. The results are applicable to installations similar to that tested when exposed to an outdoor sound field similar to that used during the measurement.

1.1.1 The facade element may be the exterior wall of a room in the building, or a portion of that wall such as a door or window, when the remainder of that wall has substantially greater sound insulation than the portion under test.

1.2 To cope with the variety of outdoor test geometry that may be encountered, several testing techniques are presented. These techniques and their general applicability are summarized in and .

1.3 This guide may be used to determine the outdoor-indoor level reduction (OILR), which is the difference in sound pressure between a specified outdoor sound field and the resulting sound pressure level in the room abutting the test facade or facade element. The outdoor sound field and its measurement must be thoroughly described. The resulting level reduction or transmission loss value will depend on the outdoor field geometry and the point at which it is measured or represented.

1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only.

This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.