Significance and Use
4.1 This classification provides a single number rating for transmission loss or noise reduction data that have been measured or calculated. This rating is based on the difference between the overall A-weighted sound level of the sound spectrum given in and the overall A-weighted sound level of the spectrum that results from arithmetically subtracting the transmission loss or noise reduction data from this spectrum. The spectrum shape is an average of three spectra from transportation sources (aircraft takeoff, road, and diesel locomotive passby). A study showed that this classification correlated well with the A-weighted and loudness reductions (see ISO 532) calculated for each of the individual spectra used in developing the rating for the one-third octave band range of 50 to 5000 Hz. The calculated numeric value of the rating is based on the sound transmission loss or noise reduction values for a particular specimen and depends only on that data and the shape of the reference source spectrum used in the calculation. The values shown in have an arbitrary reference level. Single-number ratings should always be used with caution. Specimens having the same rating can result in different indoor spectra depending on the variation of their transmission loss with frequency. Also, if the actual spectrum of the outdoor sound is different from that assumed in , the overall A-weighted outdoor-indoor noise reduction may be different from the OINIC. The strong low-frequency content of the spectrum in means that specimen achieving a high rating must have strong low-frequency transmission loss. Use of this classification with the spectrum in in situations where the source does not have a spectrum similar to could result in requirements for more low-frequency transmission loss than is necessary for the application. Examples where this can occur are stage 3 jet aircraft, high-speed freeways with sound dominated by tire noise, and train passbys with sound dominated by horns.
4.2 This classification requires sound transmission loss (TL), apparent outdoor-indoor transmission loss (AOITL(θ)), or outdoor-indoor noise reduction (OINR(θ)) data in one-third octave bands from 80 to 4000 Hz. Due to accuracy limitations given in Test Method and Guide , measurements below the 100 Hz one-third octave band are not usually reported. Studies have shown that data in the 80 Hz one-third octave band are necessary to obtain acceptable correlations for transportation sound sources. For the purposes of this classification, measurements in the 80 Hz one-third octave band are deemed to be of acceptable accuracy.
4.3 Users of this classification should recognize that low frequency measurements of sound transmission loss may be affected by the test specimen size or the specimen edge restraints, or both, particularly for small modular specimens such as doors or windows. Consequently, the outdoor-indoor transmission class (OITC) may also be affected by these factors, resulting in some uncertainty of the field performance of assemblies bearing a rating number using this classification, but to what extent is unknown.
1.1 The purpose of this classification is to provide a method to calculate single-number ratings that can be used for assesing the isolation for the outdoor sound provided by a building or comparing building facade specimens including walls, doors, windows, and combinations thereof, including complete structures. These ratings are designed to correlate with subjective impressions of the ability of building elements to reduce the penetration of outdoor ground and air transportation noise that contains strong low-frequency sound. These ratings provide an evaluation and rank ordering of the performance of test specimens based on their effectiveness at controlling the sound of a specific outdoor sound spectrum called the reference source spectrum.
1.2 In addition to the calculation method, this classification defines some ratings not defined in other standards. Other standards may define additional ratings based on the method of this classification.
1.3 The rating does not necessarily relate to the perceived aesthetic quality of the transmitted sound. Different facade elements with similar ratings may differ significantly in the proportion of low and high frequency sound that they transmit and the spectra of sources can vary significantly. It is best to use specific sound transmission loss values, in conjunction with actual spectra of outdoor and indoor sound levels, for making final selections of facade elements.
1.4 Excluded from the scope of this classification are applications involving noise spectra differing markedly from that shown in . Thus excluded, for example, would be certain industrial noises with high levels at frequencies below the 80 Hz one-third octave band, relative to levels at higher frequencies, and any source, including some transportation sources, that does not have a spectrum similar to that in . However, for any source with a spectrum similar to that in , this classification provides a more reliable ranking of the performance of partitions and facade elements than do other classifications such as Classification .
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 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.