1999 Volume 64 Issue 521 Pages 17-24
Variability of acoustic indexes due to the slight differences of the location of an observation point in a sound field were studied. The result is as follows: 1). The greater Variability due to slight differences in the location of an observation point were detected in the following order : First the indexes using the correlation technique (IACC); second, the indexes concerning energy rations (D, Lf, LE); third, the indexes concerning temporal characteristics (Ts, EDT, RT). 2). The Variability in octave band analysis were greater than those in the all-pass analysis. 3). The Variability of indexes concerning directional information were more numerous than those of the omni-directional indexes. 4). The measurement using a dummy head microphone has a unexpected instability due to slight angle in the turning of a dummy head. 5). These Variability of acoustic indexes depend upon the size of the space, the density of the reflections, and the spatial distribution of the reflections. Even if there are not perceptible differences of a sound field, the measurement at one point has a unexpected instability due to small changes in an observation point. The instability could be reduced by spatially averaging four responses at the peak of a regular tetrahedron. By measuring virtual sound source distribution once, the responses at both ears for every angle in the turning of a dummy head can be calculated using the database of the HRTFs. If the virtual sound source distribution is used, the directional characteristics of IACC can be obtained by only one measurement.
