Jont B. Allen
AT&T Bell Labs., Murray Hill, NJ 07974
Dana L. Kirkegaard
Kirkegaard & Associates, 4910 Main St., Downers Grove, IL 60515
Sunil S. Puria
MIT, Cambridge, MA 02139
With high-powered portable computers and digital signal processing boards it is possible to make high-quality, broadband impulse response measurements that are minimally intrusive to audience and performers. In January 1992 the authors designed a stimulus for measurements at Symphony Hall, Boston that permitted stimulus levels near or below the audience's masked threshold. Synchronous averaging of the response increased the signal-to-noise ratio and minimized inaccuracies due to random audience and performer movement. Subsequent measurement sessions in Davies Symphony Hall, San Francisco and the Academy of Music, Philadelphia provided the opportunity to fine-tune the stimulus type, number of averages, and various source characteristics, including: spectrum, level, directionality, and placement relative to intrusion upon audience and performers. Source directionality and placement were selected to optimize convolution with recordings of solo violin. Typically, measurements are made at levels above the masked threshold following a brief announcement. There are interesting exceptions when occupied hall measurements can only be made at levels near or below the masked threshold. In either case, occupied hall measurements must be designed to minimize the intrusion upon the concert setting, particularly when working with major symphony orchestras.