N480) THE USE OF MLS BASED METHODS FOR CHARACTERISING THE EFFECTIVENESS OF NOISE BARRIERS AND ABSORPTIVE ROAD SURFACES

Maximum Length Sequence (MLS) methods are currently being specified for a wide range of applications including test methods for characterising the performance of noise barriers. The relative ease of measurement, including the absence of calibration and high noise immunity, make the method particularly attractive for in-situ measurements. The paper reviews TRL experience in exploring and using the method for characterising sound absorption and sound transmission of a range of noise barriers and road surfaces. The experimental investigations were carried out for the Transport Research Foundation. For the measurement of sound absorption some difficulties have been experienced with reflective samples. It is concluded that the method is likely to prove inaccurate for samples with low sound absorption. The measurement errors involved in characterising sound transmission are relatively small; however, anomalous results can result where discrete air gaps occur. (A)