It has been well established that impact noise at frequencies below 100 Hz is very important to occupant reaction, particularly in response to footfall noise in lightweight construction. Several new rating methods have been introduced in recent years, in part to improve the sensitivity to or correlation between the ratings and impact noise at low-frequencies. For example, the Akulite project in Sweden suggests that measurements of very low frequencies (potentially as low as 20 Hz) are required to adequately match subjective response. The authors' proposed low-frequency rating (LIR) extends to 50 Hz, similar to the existing spectrum adaptation terms in ISO 717-2. It is shown that for many assemblies, LIR is well-correlated to A-weighted level even in the presence of significant energy below 50 Hz, in contrast to some of the Akulite findings. Different rating systems are investigated with various floor-ceiling assembly types in an effort to determine if different rating systems are required to assess acoustical performance.
