Some consequences of including low frequencies in the evaluation of floor impact sound

A method for including frequencies down to 50 Hz in the evaluation of floor impact sound has become available with the new version of ISO 717-2. In addition to the single number quantity for rating the impact sound insulation, a new spectrum adaptation term has been defined. The method has been studied by the Acoustics Group of the Nordic Committee on Building Regulations. The new method has been applied to a large number of recent measuring results from the Nordic countries. It was found that the spectrum adaptation term for the extended frequency range depends on the type of floor construction, and light floor constructions are evaluated less favourably than heavy constructions. Comparison with data from a 14-year-old Swedish survey suggests that the extended frequency range leads to a higher correlation with subjective evaluation of impact noise. The consequences of applying the extended frequency range in future building regulations or in a system for sound classification of dwellings have been considered. However, there are several problems to be solved, among which are a lack of available data for floor constructions at low frequencies, an increased measurement uncertainty, and the fact that some floor constructions are evaluated too favourably by the new method.