Evaluating STC and other single number ratings of airborne sound insulation by comparison with Zwicker loudness

One of the primary uses of single number ratings, such as STC (Standard Transmission Class), is to estimate subjective evaluations of airborne noise isolation, which are commonly determined by surveys or listening tests. Such testing showed that STC did not adequately describe the isolation of a partition compared to arithmetic averages, which helped lead to the development of Speech Privacy Class. Due to the challenges in conducting such tests, subjective data are not available for many wall types and sources of interest. It has been shown that calculated loudness can be used to assess single number ratings. This method is applied to a large dataset of laboratory wall tests and used to compare the perceived loudness with common single number ratings, including STC with and without the 8 dB rule. The effectiveness and applicability of single number ratings are discussed, and new ratings are considered.