Tentative Recommended Practice for MEASUREMENT OF AIRBORNE SOUND INSULATION IN BUILDINGS
|Publication Date:||1 January 1967|
|ICS Code (Acoustics in building. Sound insulation):||91.120.20|
Measure of Acoustical insulation -This recommended practice establishes uniform procedures for the determination of field. Transmission loss (see 4.3, 4.4, and 4.5), that is, the airborne sound insulation provided by a partition (see Note 1) already installed in & building. It also establishes, in Appendix Al a standard method for the measurement of the noise reduction between two rooms in a. building, that is, the difference in average sound pressure levels in the rooms on opposite sides of the test partition. Where the test structure is a complete enclosure out-of-doors, neither the field transmission lose nor the noise reduction is appropriate; instead, a method is established for determining the insertion loss, also in Appendix A1.
Note 1-The word partition includes In its meaning partitions, walls of all kinds, Boon. or any other boundaries separating two spaces, not necessarily enclosed. The boundaries may be permanent, operable, or movable. A ceiling plenum path (7)2 is also included, though special efforts will be necessary to eliminate flanking transmission through the common wall (see Appendix A4). In this case, the result are comparable to noise reduction rather than to transmission loss.
Note that the noise reduction evaluate the effective acoustical isolation between a pair of adjacent rooms, whereas the field transmission loss refer only to the insulation which a partition interposes in the sound path through it.
Types of Field Situation-The conditions specified (2)2 for laboratory measurement of the transmission loss for airborne sound. in which the sound fields on opposite sides of the test partition are highly diffuse, very nearly conform to the mathematical model upon which the best available theory is based. Moreover, the greatest body of practical experience deals with transmission loss measurements under such conditions.
Unfortunately highly diffuse fields are not always found in the field; and, the special efforts which would be required to simulate laboratory conditions .in the field are often impractical; in any case, they would violate the present meaning of & field test.
Instead, this recommended practice gives measurement procedures for determining the field transmission loss in nearly all cases that may be encountered in the field; no limitation to room-to-room transmission is intended. Thus several different test procedures are given, each suited to a specific of measurement situation; the appropriate measurement procedure must be selected for each field test according to the type of situation which that particular case most closely resembles Because it is well-known, the laboratory diffuse-field measurement procedure is described first in this recommended practice, an adaptation of the laboratory test method for use in the field being given in detail in the main body of the tat (see Section 6). The alternative test procedures which will be required in field situations where diffuse sound fields do not exit on both sides of the test partition are given in Appendix A2, along with criteria. for determining which alternative procedure is appropriate.
These alternative procedures are not interchangeable. In particular, it must not be expected that the alternative procedures will yield the same test values of field transmission loss. For example, the application of the different procedures to evaluate a given wall in place is likely to lead to results that do not agree, because only one of the procedures will be appropriate to that situation. On the other hand if the same kind of partition is installed in two different locations and the appropriate test procedure is used for each case, the test results may not agree because the wall exhibits different attenuation characteristics depending on the incident sound field (see 3.3, 3.4, and 3.5)
Field transmission loss data should not be reported as confirming to this recommended practice for any field situation that does not conform to a type for which a measurement procedure is given in Section 6 or Appendix A2 (see 1.3 however).