SOUND ATTENUATION OF ACOUSTIC SHIELDS

Résumé

Acoustic shields are devices used for controlling de sound energy reaching musicians seating in front of loud instruments (mainly brasses). They consist of plastic plates located at the head level of the musician intended to be protected. There have been studies where attenuations of those devices were measured in laboratory environments. The object of the present study was to assess the attenuation in a real-life situation, with musicians seated in the pit of the Four Seasons Centre for the Performing Arts, during 10 performances of the ballet Le Petit Prince by the National Ballet of Canada. Each set of measurement was done using two dosimeters: one located on the shield, and the other attached to the shoulder of the musician intended to be protected. Dosimeters were set up to measure Leq,A during the entire session of approximately 3.5 hrs. The attenuation of the shield was calculated as the difference between the readings of both instruments. In all there were 26 pairs of measurements involving two types of acoustic shields: Wenger and model 2000 Manhasset. Several measurements were repeated two and three times to confirm their repeatability. The average attenuations were of 2.67 dB and -2.14 dB for each of the two types of shields, well within the range of a field sound level measurement. The measured sound levels both in front and on the back of the shields are the results of sound energy attenuated by the shield as well as the generated by adjacent musicians, by the musician himself and the reflected from surrounding hard surfaces. Therefore the results have to be interpreted as only the influence of the shield in the presence of all other surrounding sounds. The net result is that shields do not reduce significantly the noise exposure of the musician they are supposed to protect.