Compliance and vegetated-barrier acoustical testing in a purpose-built sound-transmission suite

Random-incidence transmission losses and absorption coefficients of a vegetated noise barrier of Criblock{trade mark, serif} construction were measured without and with plants in a sound-transmission suite built specifically for the purpose, constructed from concrete noise barriers, with the vegetated barrier separating source and receiver rooms. The suite was tested for compliance with ASTM E90-09, and found to be substantially but not completely in compliance with respect to uniformity of steady-state levels and surface absorption. It was found that the transmission loss of the vegetated barrier ranged from 42 dB at low frequencies to 66 dB at 1000 Hz; above 1000 Hz only a lower limit of the TL could be determined -- values of 57-62 dB were found. These values are at least 25 dB higher than recommended by BC Ministry of Transportation guidelines. The absorption coefficients of the unplanted and planted barriers were measured; the plants decreased the absorption slightly, from NRC 0.42 to 0.37.