No noise increase
Some say that the sound increases when you move away from the acoustic screen. The results of the studies are clear: no increase in noise behind the barrier.
The main objective of a noise barrier is to significantly reduce the noise from unwanted external nuisances. In Beaconsfield, it is therefore a question of reducing the resonances due to highway traffic for the inhabitants near the tracks.
CALTRANS, the equivalent of MTQ in California, has installed hundreds of kilometers of acoustic barriers. This extract from the protocol, prepared by CALTRANS in 2013, assesses and rejects several theories raised by opponents of acoustic barriers. This includes increased noise from residents as you move further away from the highway.
RELEVANT QUOTE:
“CALTRANS has never measured an increase in noise (above measurements without an acoustic barrier) at any distance behind the noise barrier. The explanation given is that “waves of noise passing over the wall and returning to the floor” are called diffraction and are actually responsible for the reduction of noise, rather than an increase in noise ” P.4-9
The diffraction phenomenon corresponds to the moment when a sound wave reaches the end of an obstacle and then leaves in all directions. The new secondary waves therefore center on the obstacle, they are called diffracted waves. The noise reaches the acoustic shadow area of the building, albeit attenuated but not completely eliminated.
A barrier must therefore largely absorb the waves received and limit the transmission phenomena as much as possible. The proportion of reflected waves can be more or less important. Finally the diffraction phenomenon cannot be prevented, it is present by default.