ABSTRACT

Attention to sound insulation at frequencies under 100Hz is increasing. However, in current standards for assessing sound insulation the frequency range is normally limited to frequencies above 100-125Hz. For lower frequencies the measurement cannot be made since the sound fields in both the source and receiving rooms are not sufficiently diffuse to meet the requirements of conventional standards. In this paper, existing investigations concerning measurement techniques and prediction models for sound insulation at low frequencies in small rooms are reviewed. With regard to the measurement methods, it appears that although unacceptable variations in inter-laboratory measurements have been intensively discussed since the 1950s, little has been done towards developing a suitable measurement method. Thus there is still a recognised need for a better method for measuring sound insulation at low frequencies in laboratories. It would also be useful to develop a suitable engineering and survey grade measurement method. As to the prediction models, although a number of prediction models has been developed for sound insulation, it appears that only one using the finite element method is relatively accurate and practical for low frequencies.