5.1 The main part of this standard uses procedures originally developed for laboratory measurements of the sound transmission loss of partitions. These procedures assume that the rooms in which the measurements are performed 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. Experience and controlled studies (1)6 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 m³. 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 are measurable between larger spaces that meet a limitation on absorption in the spaces to provide uniform sound distribution.

5.2 Annex A1 was developed for use in spaces that are very large (volume of 150 m³ or greater). Sound pressure levels during testing vary markedly across large rooms so that the degree of isolation varies 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.

5.3 Several metrics are available for specific uses. Some evaluate the overall sound isolation between spaces including the effect of absorption in the receiving space and some evaluate the performance or apparent performance of the partition being evaluated. The results obtained are applicable only to the specific location tested.

5.3.1 Noise Reduction (NR) and Noise Isolation Class (NIC)—Describe the sound isolation found between two spaces. Noise reduction data are based on the space- and time averaged sound pressure levels meeting the requirements of 11.3 or A1.3 as required depending on the sound absorption, volume, and shape requirements of 9.2. Noise reduction values are influenced by the absorption in the receiving space as well as the apparent performance of the partition. The noise reduction values in unfurnished spaces are typically less than in furnished spaces, and noise reduction values between the spaces depend on the test direction used and the sound absorption in the spaces. However, these effects are lessened when the method of Annex A1 is used.

5.3.2 Normalized Noise Reduction (NNR) and Normalized Noise Isolation Class (NNIC)—Describe the sound isolation between two residential or office spaces meeting the requirements of 9.3.1 adjusted to standardized room conditions typical of such spaces when normally furnished.

5.3.3 Apparent Transmission Loss (ATL) and Apparent Sound Transmission Class (ASTC)—Describe the apparent sound insulation of a partition separating two spaces as influenced by flanking in the supporting structure. All sound transmission, including any flanking transmission, is ascribed to the partition. The apparent transmission loss of the partition will be less than the actual sound transmission loss (Path D in Fig. 1) if flanking (Path F in Fig. 1) is significant (2,3). These results are in theory the same in each direction but differences with direction have been observed in practice. If it is necessary for diagnostic purposes to suppress flanking when doing measurements, the results must be clearly labeled as “flanking suppressed.”

5.4 The primary use of this test method is to evaluate the sound isolation and apparent sound insulation performance in buildings based on tests of unmodified structures. If the measurement methods are used for diagnostic or investigative purposes to measure the performance of modified structures in buildings, results must be clearly labeled to indicate such.

Note 3: Versions of this standard prior to 2017 included TL and STC metrics with prefixes designated as “Field (F).” The “Field” version of the metrics was intended to exclude the presence of flanking sound transmission altogether; whereas, the “Apparent” version presumes an (unknown) degree of flanking. In addition, the “Field” version of the metrics required more stringent limits on room volume and room absorption. These earlier versions also included guidance on suppression of flanking, useful for diagnostic purposes.

1.1 The sound isolation between two spaces in a building is influenced most strongly 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, referred to as flanking paths. Fig. 1 illustrates the direct paths (D) and some possible structural flanking paths (F). Additional non-structural flanking paths include transmission through common air ducts between rooms, or doors to the corridor from adjacent rooms. Sound isolation is also influenced by the size of the separating partition between spaces and absorption in the receiving space, and in the case of small spaces by modal behavior of the space and close proximity to surfaces.

FIG. 1 Direct (D) and Some Indirect or Flanking Paths (F and Dotted) in a Building

1.2 The main part of this test method defines procedures and metrics to assess the sound isolation between two rooms or portions thereof in a building separated by a common partition or the apparent sound insulation of the separating partition, including both direct and flanking transmission paths in all cases. Appropriate measures and their single number ratings are the noise reduction (NR) and noise isolation class (NIC) which indicate the isolation with the receiving room furnished as it is during the test, the normalized noise reduction (NNR) and normalized noise isolation class (NNIC) which indicate the isolation expected if the receiving room was a normally furnished living or office space that is at least 25 m³ (especially useful when the test must be done with the receiving room unfurnished), and the apparent transmission loss (ATL) and apparent sound transmission class (ASTC) which indicate the apparent sound insulating properties of a separating partition including both the direct transmission and flanking transmission through the support structure. The measurement of ATL is limited to spaces of at least 25 m³ where modal effects create fewer problems. With the exception of the ATL and ASTC under specified conditions, these procedures in the main part of the test method 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 including those that are permanent, operable, or movable.

1.3 The NR and NIC between two locations are always measureable and reportable though conditions present will influence how measurements are performed. With one exception (see 13.5.1), it is required that the NIC always be reported. Restrictions such as minimum room volume or dimensions or maximum room absorption are imposed for all other measures and ratings in this standard. Thus, conditions sometimes exist that will not allow NNR (NNIC) or ATL (ASTC) to be reported. Where a partition between rooms is composed of parts that are constructed differently, or contains an element such as a door, the ATL and ASTC of the individual elements or portions of the partition are not measurable without modifications to the rooms. To evaluate the field performance of a door less than 6 m² in area, use Test Method E2964. The various metrics are inherently different quantities, so that NIC cannot be used instead of NNIC or ASTC to evaluate compliance with a specification when the specification is written in terms of one of those metrics that cannot be reported with the conditions present.

1.4 Annex A1 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 This test method is intended to evaluate the actual acoustical performance between rooms in buildings. Thus, it forbids temporary modifications that influence performance. The measurement methods are useful in diagnostic situations where modifications are made. In such cases reports of results are required to clearly indicate that such modifications were made.

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

1.7 The text of this test method references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

1.8 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.