Measurement of Transmission Functions in Lightweight Buildings for the Prediction of Structure-Borne Sound Transmission From Machinery

Abstract

This paper develops and assesses protocols for the measurement of transmission functions in lightweight buildings. A transmission function is defined that relates the spatial-average sound pressure level in a room to the structure-borne sound power injected into a wall or floor. The intention is to facilitate the prediction of structureborne sound transmission from machinery to receiving rooms. Errors in the measurement of the power input can be reduced by using a pair of accelerometers on either side of the excitation point rather than a single accelerometer on one side. Laboratory measurements on a timber-frame wall indicate that steady-state excitation using an electrodynamic shaker and transient excitation with a force hammer can be considered as equivalent. Measured transmission functions from a laboratory test construction below 500 Hz are found not to be significantly affected by the choice of excitation position being directly above a stud or in a bay. Laboratory and field results on different timber-frame walls indicate that with transient excitation using a force hammer, the transmission function is measurable in vertically-, horizontally- and diagonally-adjacent receiving rooms over the frequency range from 20 to 1 kHz. The approach has been applied in field measurements which indicate that there is potential to create databases of average transmission functions as a simplified prediction tool for sound pressure levels from service equipment in buildings.