ASA 127th Meeting M.I.T. 1994 June 6-10

4aEA1. Measurement of transmitted and diffracted sound through open screens by impulse methods.

Richard Lyons

Sheffield Hallam Univ., School of Construction, Pond St., Sheffield S1 1WB, UK

Barry M. Gibbs

Liverpool Univ., Liverpool L69 3BX, UK

The availability of inexpensive but powerful instrumentation and the rising costs of specialist acoustic facilities have increased interest in impulse response methods for measuring sound insulation, particularly in situ. The method is relatively simple and requires the separation of a direct short duration transmitted signal from subsequent scattered, diffracted, and reflected components, to allow fast Fourier transformation. Where the sound insulation performance of an open acoustic screen is required, internal diffracted components are included in the time window of interest. A description is given of the method of measurement of open screens that applies to both laboratory and field conditions. Measurements are compared with theory and discrepancies are the result of phase changes at high frequencies. These phase changes are not included for in the thin screen theory, however, agreement in general is good. The method works well for open screens, provided that the time signal is properly isolated, and promises a quick accurate method of measurement for complicated open screen geometry's where theoretical prediction is difficult.