Timbral aspects of reproduced sound in small rooms. II

This paper is a report on some of the influences of individual reflections on the timbre of reproduced sound. Bech [J. Acoust. Soc. Am. 97, 1717-1726 (1995)] gave the first report. A single loudspeaker with frequency-dependent directivity characteristics, positioned in a room of normal size with frequency-dependent absorption coefficients of the room surfaces, has been simulated using an electroacoustic setup. The model included the direct sound, 17 individual reflections and the reverberant field. The threshold of detection, and just-noticeable differences for an increase in level were measured for individual reflections, using four subjects for noise and three for speech. The results have confirmed the findings of the first report that the first-order floor reflection is likely to individually contribute to the timbre of reproduced noise. However, for a speech signal none of the investigated reflections will contribute individually to the timbre. It is suggested that the threshold of detection is determined by the spectral changes in the dominant frequency range of 500 Hz-2 kHz. For increases in the level of individual reflections, the most likely to be audible is the first- order floor reflection, for speech and noise. For a noise signal, additional reflections from the wall to the left and behind the listener also belong to this group.