I.R.C.A.M., 1 place Igor Sravinsky, 75004-Paris, France
Conventional loudspeaker radiation patterns have no relationship to those of the sound sources which they purport to simulate [Causse et al., Proceedings of I.S.M.A. Tokyo, 67--70 (1992)]. In this particular study, the perceptual difference between a real instrument and a programmable radiation pattern loudspeaker system (12 independently programmable loudspeakers mounted on a polyhedral structure) was investigated. In a first experiment, the trombone was chosen for its radiation pattern which presents a cylindrical symmetry and a monotonic variation according to frequency. For purposes of reproducibility during perceptive tests, the programmable radiation pattern loudspeaker was compared with an artificially driven trombone: The musical material was recorded just after the U-bend of the bell joint. This signal was reproduced by a driver, corrected by inverse filtering techniques, and mounted at the same location. To supply the programmable radiation pattern loudspeaker system, close-microphone recordings on axis and off axis were used. The programmable loudspeaker was controlled with the help of filtering processes that were calculated from previous measurements on the radiation pattern of the trombone. Results of the listening tests will be presented and discussed.