Sound absorbing chandeliers for multitalker noise control in large halls

During social gatherings in large halls, multiple conversations taking place simultaneously can lead to very high noise levels. Increasing the amount of sound absorption in the hall can be very effective in this context: due to the Lombard effect, the noise level drops with 6 dB when doubling the equivalent absorption area, while only a 3 dB drop occurs for sources of constant sound power. However, the possibilities for the absorptive treatment of existing venues can be highly limited, especially when dealing with architectural heritage. Therefore, in the present study, sound absorbing chandeliers, consisting of dense arrangements of absorbing objects, have been designed, developed, tested, and applied in a hard-walled historic hall that hosts social gatherings of more than 800 people. Experiments in the hall during busy events have confirmed the effectiveness of the chandeliers, yet it was also found that, since the ceiling has become the main absorptive surface, they loose efficiency due to the resulting sound field directionality. Furthermore, the individual vocal effort was observed to stay constant when the background nose level was decreasing. Both effects have been thoroughly studied and analyzed, and a prediction methodology to account for these effects has been proposed.