Improvement of verbal communication in the Jubileumzaal of the historic KU Leuven University Hall

The Jubileumzaal is a large room at the KU Leuven University Hall which is used for social gatherings such as receptions and technical exhibitions.The room has a nominal capacity of 800 persons and it suffered from long-standing complaints about high noise levels and poor speech intelligibility.The main cause was the excessive reverberation time, which amounted to an average value of 5.1s across the 500, 1000 and 2000 Hz octave bands.However, due to the historical character of the room, the options for acoustic renovation were extremely limited.In the end, custom-made sound-absorbing chandeliers with integrated lighting were retained as an architecturally acceptable option.A total of 20 chandeliers were placed in the room, which reduced the reverberation time to 2.2 s, in close agreement with a theoretical assessment that accounts for the sound field directionality.In order to assess the effectiveness of the refurbishment, noise measurements were conducted during busy receptions before and after renovation.They are in good agreement with a prediction model that accounts for the Lombard effect, at least when the number of persons in the room is increasing.When it is decreasing, the measured noise levels are substantially higher, and an extension of the prediction model is offered to explain this result.