Sensitivity of stage acoustic parameters to source and receiver directivity : measurements on three stages and in two orchestra pits

Stage acoustic parameters are commonly determined in concert halls using omnidirectional transducers, but might be more valid when using directional transducers. In this paper, the sensitivity of stage acoustic parameters to source and receiver directivity has been investigated by measurements on three stages and in two orchestra pits. A single loudspeaker was used with a directivity similar to a trumpet, aimed in 12 evenly spread directions. As a directional receiver, a head and torso simulator (HATS) was used with its viewing direction towards the conductor position. Measurements were also taken with (nearly) omnidirectional transducers. i.e. a dodecahedron loudspeaker and a single microphone. The investigated stage acoustic parameters measuring reverberation time and reflected sound levels were sensitive to the directivity of the measurement transducers. The parameters dealing with early sound, EDT and STearly,d, are more sensitive than the parameters dealing with late sound, T20 and STlate,d. When comparing results measured with a head and torso simulator to results measured with an omnidirectional microphone, the EDT tends to be lower and the STearly,d higher for the ear directed towards the sound source. The results of measurement using the directional source show that EDT and T20 have lowest values and STearly,d and STlate,d highest values, when the sound source is directed towards the closest surfaces that cause a first order reflection towards the receiver. Further research is necessary to determine whether the differences in parameter values would lead to noticeable differences