Sound propagation measurement using swept-sine signal

In the measurement of sound propagation outdoors, the synchronous averaging techniques using MLS signal or swept-sine signal can not be applied to reduce the influence of the background noise because of the time-variance of the sound field influenced by the meteorological conditions. Therefore, we have been investigating the method of measuring impulse response using swept-sine signals with a long duration time (up to 600 sec. per a octave band) to avoid the influence by wind and atmospheric turbulence and to get a high signal-to-noise ratio. In order to examine the applicability of this method to outdoor sound propagation measurement, numerical study, scale model experiment using a 1/40 wind tunnel and field measurement of sound reduction index of a building facade have been conducted. As a result, it has been found that the results obtained by the method using a long swept-sine signal and those obtained by the ordinary method using a stationary-random noise are in high correspondence. As another application, the measurement of sound propagation characteristics from a semiunderground road will be presented.