TOWARDS AN IN-DIRECT METHOD FOR LOW FREQUENCY SOUND TRANSMISSION

This paper describes the development and testing of an alternative method of sound transmission measurement, ideally suited to low frequencies. The standard approach to measuring sound transmission (detailed in ISO 10140) relies on the assumption of a diffuse field from which radiated sound power can be estimated. While adequate for higher frequencies, this assumption doesn’t hold at low frequencies due to the presence of modal effects. The proposed method avoids this assumption and thus has the potential to provide a low frequency sound transmission measurement with reduced uncertainty. This is achieved by a) representing the radiated sound field by an equivalent array of monopole sources (i.e. volume velocities) which are independent of the room’s modal characteristics and b) applying a synthesised incident diffuse field to a measured vibro-acoustic FRF of the partition. Preliminary results demonstrate that the equivalent field representation is both invariant of the rooms modal characteristics, and able to accurately reproduce the sound field radiated from a partition.