Moorhouse A., Ramadorai R.

The context of this paper is the need for reliable measurement of sound insulation at low frequency. Since 2003, the Building Regulations in the UK have placed more emphasis on low frequency performance. However, this has led to greater variance in ratings given to nominally identical constructions because of the unreliability of low frequency measurements according to ISO140. There are several components to the variance, and this paper addresses one of these, i.e. the question of how to obtain a reliable average of the sound pressure throughout a room at low frequency. A room modes model is used to investigate the optimum positioning of microphones. It is shown that the true average sound pressure level is closely approximated by the average of six microphones equally spaced along the diagonal of a rectangular room. These findings are confirmed by measurement.