Noise Propagation Measurement by Synchronized Integration Technique

Abstract

A new technique to measure the ground to ground noise propagation was developed. The test sound of a band limited noise is emitted from a loudspeaker intermittently. A several second burst of the noise and the following pause of the same length are repeated. At a receiving spot, the sound intensity is integrated alternatively by two digital counters. One counter integrates the intensity of the test sound plus the background noise at that spot in the period for which the test sound is present. The other integrates the intensity of the background noise in the absent period of the test sound. Each of the devices at the source and receiving spots has a precise crystal oscillator as the clock. Once the synchronization of the two devices is made before a measurement, the relative phase of the operations of the devices is kept constant during the time of the measurement without any connection. After the completion of a predetermined number of integrations, the difference of the accumulated numbers in the two counters is read, which gives the intensity of the test sound at the receiving spot. Experiments using a 5-Watt loudspeaker showed that the noise attenuations of the distance of 170m can be measured with the statistical error less than 0. 5dB.