Airborne Sound Level Difference between Dwellings at Low Frequencies

Abstract

This paper describes work on the relationship between laboratory measurements of the sound insulation of walls and floors, and the sound level difference between dwellings at frequencies below 200 Hz. The aim of the work was to describe the sound transmission between sound fields in small rooms and at low frequencies in terms of the modal characteristics of the spaces and of the intervening walls/floors. An experimentally validated finite element method (FEM) model was developed and a parametric survey conducted on the effects on sound level difference of construction, room/wall dimension and the absorption of surfaces and contents. The existing international standard ISO 140 gives a diffuse field correction to the sound reduction index, to give the level difference. This paper proposes a supplementary correction, which is a function of the low frequency characteristics of the separated rooms and of the walls/floors. In addition a statistical estimate is given of level difference for the range of likely conditions between dwellings for both heavyweight masonry walls and lightweight cavity walls.