Active and Passive Acoustics Comparison of Performance Characteristics and Practical Application Possibilities, Presentation of a Case Study

This spring the largest theatre building ofthe Netherlands, the Chasse Theatre at Breda has been completed.0f the two main auditoria, which have similar stage houses, one has electronic variable acoustics by means of a SlAP-system (System for Improved Acoustic Performance) including a stage system, and the other has mechanical variable acoustics which includes a large orchestra shell, It will be shown through measurements that active (electronic) acoustics can he just as effective as passive (physical) acoustics.It is particularly interesting that loudness, reverberation time and reflection patterns can be influenced more independently with active systems, which flexibility is an advantage for meeting the needs of performers.Furthermore active control of acoustics can also provide a significantly improved foldback to actors and singers for drama, opera performances etc., when technical stage facilities and scenery make physical acoustic means difficult to apply. INTRODUCTIONThe authors of this paper are working as acoustic, electro-acoustic and theatre consultants in the consultancy of Prinssen and Bus Consulting Engineers at Uden, The Netherlands.Consultancy practice showed that for many existing auditoria the desired acoustic improvements can only be achieved electro»acoustically and that for many existing, as well as new auditoria, electronic variable acoustics are more practical and cost effective than mechanical variable acoustics.This was the reason to develop a technology which resulted in a fully variable acoustic for auditoria and other public spaces, using the very latest digital electronics.Each auditorium has its own unique acoustic characteristics which in the opinion of the authors should remain true also for electronically enhanced acoustics.Starting from the constultancy s experience with natural, that is mechanical or "passive" variable acoustics, the electronic system would have to modify a hall's acoustic by filling in the missing reflections from each surface and even, electronically, move these surfaces to acoustically more desirable "positions".This way the natural acoustic and electronic enhancement together provide the desired acoustic, contrary to techniques which simply put the electronic acoustic over the natural acoustic.The result of this development is called "System for Improved Acoustic Performance' (SIAPl.SIAP offers control over the acoustic parameters of a room offering significant yet subtle improvement of the acoustics by influencing both the early and the late sound energy in the room ("active' variable acoustics).For funher details regarding the working of the system and its performance.see ( 1) and (2).