Auditory localization was studied in a room bounded by a single acoustically reflective surface. The position of that surface was varied so as to simulate a floor, a ceiling, and left and right side walls. The surface ~as eliminated in one condition so that we could examine localization in free field for purposes of comparison. Using a source identification method we assessed the influences of these various room configurations on the localization of both slow-onset and impulsive sine tones of low frequency (500 Hz). We also measured the steady-state interaural-time-difference (ITD) and interaural-intensity-difference (lID) cues available to subjects in the different room configurations and compared these data with the perceptual judgments. Our results indicate the following: (1) A sound must include transients if the precedence effect is to operate as an aid to its localization in rooms. (2) Even if transients are present the precedence effect does not eliminate all influences of room reflections. (3) Due to the interference of reflections large interaural intensity differences may occur in a room and these have a considerable influence on localization; this is true even at low frequencies for which lID cues do not exist in a free field. (4) Listeners appear to have certain expectations about the reliability and plausibility of various directional cues and perceptually weight the cues accordingly; we suggest that this may explain, in part, the large variation in time-intensity trading ratios reported in the literature and also the differing reports regarding the importance of onsets for localization. (5) In this study we find that onset cues are of some importance to localization even in free field. PACS numbers: 43.66. Pn, 43.66.Qp, 43.55.Br [RDS] INTRODUCTION this gave the ceiling reflection an increased importance and accounted for the enhancement of localization accuracy. This paper is a report of our second experimental study It might be hypothesized, more generally, that any reof auditory localization in rooms. The first study (Hartflection will influence the localization of impulsive tones in a mann, 1983a; referenced below as paper I) was conducted in manner which is fully determined by its azimuth and by its a variable-acoustics concert hall-the Espace de Projection arrival time relative to a direct sound. One purpose of the (ESPRO) at the Institut de Recherche et Coordination present study was to provide a direct test of the contribution Acoustique/Musique. The wall absorption and ceiling of reflection azimuth. To do so, we needed to be able to maniheight of the ESPRO are both manipulable, and their effects pulate the directions of acoustical reflections while preservon localization were examined for several different classes of ing the essential features of a room. We achieved this by sounds. designing a room in which there was one and only one One notable finding in the ESPRO was that the azisound-reflecting surface. The position of that surface was muthal localization of impulsive tones significantly imsystematically manipulated across conditions so that we proved when the ceiling was lowered. Since the principal could examine its impact on localization and the precedence acoustical consequence of this manipulation was to reorder effect. the arrival times of reflections from the room's boundaries, A second finding reported in paper I was that listeners we interpreted this result as indicating a limitation of the had great difficulty localizing low-frequency tones with slow precedence effect (Wallach et al., 1949; Haas, 1951; Blauert, onsets. Their highly inaccurate localization judgments were 1971; Zurek, 1980) as it operates in rooms.! nevertheless made with some consistency, as demonstrated Our attention centered, particularly, on the first reflecby the fact that the variability of those judgments was signifitions from the ceiling and side walls. The azimuth of a ceiling cantly less than chance. Apparently the listeners were able to reflection invariably agreed with the azimuth of a direct devise some strategy for localizing such sounds, albeit an sound and, as a consequence, might be expected to have reininappropriate one. As part of the present study, we conductforced listeners' sense of location. By contrast, the azimuth ed an experiment to determine how listeners attempt to cope of a side wall reflection disagreed with that of a direct sound with slow-o~set tones. For various arrangements of our and was a potential source of localization error. When the room, we compared their perceptions of the location of slowceiling was lowered, its reflection reached a listener much onset tones with measurements of the corresponding interearlier than the side wall reflections. We hypothesized that aural time and intensity cues.
REF showed that reverberation has a considerable effect on localization even at low frequencies.
Localization of sound in rooms, II: The effects of a single reflecting surface
The Journal of the Acoustical Society of America
The Journal of the Acoustical Society of America
Physics Medicine