In-situ measurements of sound reflection and sound insulation of noise barriers: Validation by means of signal-to-noise ratio calculations

Abstract

After some years from its first release, the CEN/TS 1793-5 European standard for in-situ measurement of sound reflection and airborne sound insulation characteristics of noise barriers has been significantly enhanced and validated in the frame of the EU funded QUIESST project. The procedure, based on impulse response measurements near the noise barrier and in the free field, is robust and easily applicable but much attention must be paid when: i) applying the signal subtraction technique to get the reflected signal component and ii) extracting the transmitted component, especially measuring highly insulating noise barriers. In both cases, it is essential to avoid a poor signal-to-noise ratio of the critical part of the impulse response. In the frame of the QUIESST project specific quality criteria, applicable on site, have been introduced in order to check and validate the result. These criteria are rigorously described here for the first time and illustrative examples are presented.

Sound Insulation and Reflection Properties of Sonic Crystal Barrier Based on Micro-Perforated Cylinders

“…The signal subtraction technique [33] is applied to separate a reflected component on each microphone of the grid. The technique disregards direct sound waves from both the free-field and the measurement with the barrier.…”

The use of in-situ test method EN 1793-6 for measuring the airborne sound insulation of noise barriers

“…The calculation of the signal-to-noise ratios of a measured impulse response is necessary to ensure that the measurements are not affected by background noise; EN 1793-6:2012 calls for an effective signal-to-noise ratio of at least 10 dB. A calculation method has been proposed [13] that makes use of two segments of the measured impulse responses, one representing the "signal" and the other representing the "noise" ( Figure 1). The "noise" segment is taken from the part of the impulse response immediately preceding the arrival of the directly transmitted sound, hence limiting the segment length to 3.5 milliseconds and giving the calculation a low frequency limit of 400 Hz.…”