Determination of acoustic characteristics of pneumatic exhaust silencers: a new procedure.

This paper describes the development of a standard test procedure for assessing the acoustical efficiency of pneumatic exhaust silencers. These devices are usually tested by the manufacturers by using the ISO 6358 standard which aims at determining the flow-rate characteristics. Manufacturers wish to take profit of existing ISO 6358 test benches to get also the acoustical characteristics of the silencers, namely the insertion loss and the radiated noise. Tests were carried out on 30 silencers to assess the number of microphones that are necessary to measure these data. Additional tests were performed to determine the influence of the room. A relationship between the pneumatic pressure decay and the noise decay was established, allowing the calculation of the radiated noise as a function of the initial pressure. Thus, the new test procedure will provide the end-user with the parameters to calculate the noise level at the working place in addition to the insertion loss and the mean acoustic level at 1 m and 7 bars as specified in ISO 6358. This procedure will be proposed at the next revision of the ISO standard.