This classification provides the A-weighted sound level reduction for a test specimen, based upon the sound spectrum given in Table 1. The spectrum shape is an average of three typical spectra from transportation sources (aircraft takeoff, freeway, and railroad passby). A study showed that this classification correlated well with the A-weighted and loudness reductions (see ISO 532) calculated for each of the typical spectra for the one-third octave band range of 50 to 5000 Hz. The calculated numeric value of OITC is based on the measured sound transmission loss values for a particular building facade and depends only on the shape of the reference source spectrum used in the calculation. The values shown in Table 1 have an arbitrary reference level.

This classification requires sound transmission loss (TL) measurements in one-third octave bands from 80 to 4000 Hz. Due to accuracy limitations given in Test Method E90 and Guide E966, 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 of sound transmission loss in the 80 Hz one-third octave band from qualified laboratories are deemed to be of acceptable accuracy.

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 single-number rating that can be used for comparing building facade designs, including walls, doors, windows, and combinations thereof. This rating is designed to correlate with subjective impressions of the ability of building elements to reduce the overall loudness of ground and air transportation noise. It is intended to be used as a rank ordering device.

1.2 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. 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.

1.3 Excluded from the scope of this classification are applications involving noise spectra differing markedly from those described in 4.1. 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. However, for any source with a spectrum similar to those in 4.1, this classification provides a more reliable ranking of the performance of partitions and facade elements than do other classifications such as Classification E413.

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

1.5 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.