Development and performance assessment of sound absorbing chandeliers for reverberation control and improved verbal communication in large rooms

Options for increasing the sound absorption in an existing room may be highly limited, especially when it concerns architectural heritage. In order to expand the number of possible options for large spaces, sound absorbing chandeliers with integrated lighting have been developed and their performance for reverberation control and for the reduction of background multitalker speech noise has been investigated. Prototypes of several chandelier designs have been constructed by assembling existing absorbing elements into relatively dense arrangements. Reverberation room tests have confirmed that the equivalent absorption area of such a chandelier can be approximately predicted from relevant sound absorption data of its constituting elements. When sound absorbing chandeliers are suspended from the ceiling in a room such that the ceiling is the main absorptive surface, the inhomogeneous absorption distribution over the room results in a directional sound field and this leads to a loss of efficiency for reverberation time control. The loss has been quantified, both numerically for a set of rooms, and experimentally for a large historic room. For the same rooms, the effectiveness of the sound absorbing chandeliers for the reduction of background noise during social gatherings has been assessed with a prediction model that accounts for the Lombard effect. Noise measurements have also been conducted in the historic room, during busy receptions before and after applying chandeliers. They are in good agreement with the predictions, at least when the number of persons in the room is increasing. When it is decreasing, the vocal effort is seen to remain at the maximum level, such that the background noise decreases less than expected. After confirmation with experimental data from a different room, the prediction model has been extended to account for this effect.