The main part of this standard uses procedures originally developed for laboratory measurements of the transmission loss of partitions. These procedures assume that the rooms in which the measurements are made have a sound field that reasonably approximates a diffuse field. Sound pressure levels in such rooms are reasonably uniform throughout the room and average levels vary inversely with the logarithm of the room sound absorption. Not all rooms will satisfy these conditions. Practical experience and controlled studies (1) have shown that the test method is applicable to smaller spaces normally used for work or living, such as rooms in multi-family dwellings, hotel guest rooms, meeting rooms, and offices with volumes less than 150 cubic meters. The measures appropriate for such spaces are NR, NNR, and ATL. The corresponding single number ratings are NIC, NNIC and ASTC. The ATL and ASTC may be measured between larger spaces that meet a limitation on absorption in the spaces to provide uniform sound distribution.

Annex A2 was developed for use in spaces that are very large (volume of 150 m³ or greater). Sound pressure levels during testing can vary markedly across large rooms so that the degree of isolation can vary strongly with distance from the common (separating) partition. This procedure evaluates the isolation observed near the partition. The appropriate measure is NR, and the appropriate single number rating is NIC.

It is sometimes necessary to demonstrate that the sound insulation of a partition meets or exceeds a specific criterion. Annex A1 provides additional requirements, and describes how shielding procedures can be used to reduce flanking transmission in stages to show that a partition has achieved a minimum value of the FTL or minimum value of the FSTC which may meet or exceed the criterion. If it is demonstrated that no significant flanking exists through shielding of all potential flanking paths, then, and only then, FTL and FSTC may be reported without qualification.

Note 3—Measuring the sound transmission loss properties of a partition itself to demonstrate that it meets or exceeds a specific criterion is very difficult in the field due to the presence of flanking (2, 3). Room volume and absorption requirements must also be met.

Several metrics are available for specific uses:

Noise Reduction (NR) and Noise Isolation Class (NIC)—Describe the sound isolation between two spaces in the condition found. The measurement method varies depending on the size of the spaces. When each space is less than 150 cubic meters, sound levels are averaged over the space. NR values for such spaces when unfurnished will usually be lower than values measured when the spaces are furnished. These values relate directly to the sound attenuation experienced by occupants of the spaces for the condition evaluated, including the effects of flanking and room absorption, and not just to the performance of a partition. Therefore results may be different when measured in different directions. When either of the spaces is 150 cubic meters or more, sound levels are measured in an area close to the partition on each side. These results include some effect of room absorption and flanking, but the effect of room absorption is less when measured close to the partition.

Normalized Noise Reduction (NNR) and Normalized Noise Isolation Class (NNIC)—Give the sound isolation between two residential or office spaces adjusted to standardized room conditions. This normalization is usually done to compensate for a lack or excess of furnishings in the rooms. NNR and NNIC shall not be used for spaces of 150 cubic meters or larger. These values are intended to relate to the sound attenuation experienced by occupants of the spaces if the spaces were normally furnished. Results are applicable only to the designated receiving room.

Apparent Transmission Loss (ATL) and Apparent Sound Transmission Class (ASTC)—Describe the apparent sound insulation of a partition separating two spaces. All sound transmission, including any flanking transmission, is ascribed to the partition. The actual transmission loss of the partition will usually be higher than the apparent transmission loss. These results are in theory the same in each direction but may differ with direction in practice.

Field Transmission Loss (FTL) and Field Sound Transmission Class (FSTC)—These results should theoretically approach the actual sound insulation of a partition or partition element as would be measured in a laboratory, but in practice they often do not. These values may be reported only if the stringent requirements of Annex A1 to reduce flanking transmission are met. Since all flanking is removed to obtain these metrics, they do not reflect the sound attenuation experienced by the occupants when flanking transmission is significant. These results are in theory the same in each direction but may differ with direction in practice.

Note 4—Since the metric ASTC includes the effect of direct and flanking transmission, the ASTC will be less than or equal to the FSTC. The difference depends on the magnitude of the flanking transmission. Thus, the ASTC can be used to demonstrate that a partition at least meets an FSTC requirement and may exceed it. If ASTC is measured under conditions that do not satisfy the more stringent requirements in Annex A1, this may introduce other variations.

1.1 The sound isolation between two spaces in a building is determined by a combination of the direct transmission through the nominally separating building element (as normally measured in a laboratory) and any transmission along a number of indirect paths, usually referred to as flanking paths. Fig. 1 illustrates the direct paths and some possible structural flanking paths. Additional non-structural flanking paths may include transmission through common air ducts between rooms, or doors to the corridor from adjacent rooms.

1.2 The main part of this test method defines procedures and metrics to assess the sound isolation between two rooms in a building separated by a common partition including both direct and flanking transmission paths. Appropriate measures and their single number ratings are the noise reduction (NR) and noise isolation class (NIC), the normalized noise reduction (NNR) and normalized noise isolation class (NNIC), and the apparent transmission loss (ATL) and apparent sound transmission class (ASTC). With the exception of the ATL and ASTC under specified conditions, these procedures are only applicable when both room volumes are less than 150 m³.

Note 1—The word “partition” in this test method includes all types of walls, floors, or any other boundaries separating two spaces. The boundaries may be permanent, operable, or movable.

1.3 Annex A1 provides methods to assess the sound transmission through a partition or partition element with the influence of flanking transmission reduced. These methods may be used when it must be demonstrated that a partition has achieved a specified minimum sound attenuation. The results are the field transmission loss (FTL) and field sound transmission class (FSTC).

1.4 Annex A2 provides methods to measure the sound isolation between portions of two rooms in a building separated by a common partition including both direct and flanking paths when at least one of the rooms has a volume of 150 m³ or more. The results are the noise reduction (NR) and noise isolation class (NIC).

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of 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.