Takenaka Tech. Res. Lab., 2-5-14 Minamisuna, Tokyo 136, Japan
975 Memorial Dr., #804, Cambridge, MA 02138
Spaciousness, subjective broadening of the musical source, and envelopment, subjective immersion of the listener in the reverberant sound field, are measured by IACC[sub Early] and IACC[sub Late], respectively, in concert halls using binaural recordings from small microphones placed at the entrance of a person's ear canal. IACC's replace LF measured with a figure-8 microphone, which fails to evaluate reflections from suspended panels and lateral reflections at small angles. Validity of real heads in comparison with artificial heads is confirmed. Measurements reveal difference between early and late as 80 ms, consistent with other orthogonal room measurements. An hearing importance curve is constructed to justify averaging the measured IACC's in four 500- to 4000-Hz octave bands, yielding, IACC[sub E4] and IACC[sub L4]. The IACC's must be derived from exact measurement of impulse response; the authors use a stretched pulse signal from a omnidirectional source. Preferred source positions and seats for measurements in halls are stated. Processing time is about 15 min to obtain the two IACC's for one source/receiver position. Comparisons of IACC's measured in unoccupied prominent US and European halls show that IACC[sub E4]'s correlate well with subjective judgments made on a scale from good to excellent, where all halls have low values of IACC[sub L4]'s.