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

The transmission loss and absorption coefficient of a vegetated noise barrier of Criblock™ construction were measured in a sound-transmission suite built specifically for the purpose. The suite was tested for compliance with the ASTM E90-09 standard and found to be substantially, but not perfectly, in compliance. 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 on the TL could be determined — values of 57-66 dB were found. These values are at least 25 dB higher than recommended by local transportation-authority guidelines. The absorption coefficients of the unplanted and planted barriers were measured; the plants decreased the absorption slightly, from noise reduction coefficient 0.42 to 0.37.