The use of single number ratings in describing the acoustic performance of various building elements is very common. Examples of this are the sound‐transmission class (STC) of a wall or the impact‐noise rating of a floor. In the STC rating method, a transmission‐loss (TL) curve of irregular shape is compared to a standard‐reference curve. The contribution of various frequency bands depends on the shape of the standard curve and the method of comparison. An experiment has been carried out to determine the relative subjective importance of the various frequency bands and how the change in subjective rating due to irregularities in a TL curve compares with the rating obtained by using the standard curve and fitting rules. Results indicate that the present STC rating system is overconservative in rating changes in a TL curve and that narrow coincidence‐type dips are not very important.

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