To a first-order approximation, binaural localization cues are ambiguous: many source locations give rise to nearly the same interaural differences. For sources more than a meter away, binaural localization cues are approximately equal for any source on a cone centered on the interaural axis (i.e., the well-known "cone of confusion"). The current paper analyzes simple geometric approximations of a head to gain insight into localization performance for nearby sources. If the head is treated as a rigid, perfect sphere, interaural intensity differences (IIDs) can be broken down into two main components. One component depends on the head shadow and is constant along the cone of confusion (and covaries with the interaural time difference, or ITD). The other component depends only on the relative path lengths from the source to the two ears and is roughly constant for a sphere centered on the interaural axis. This second factor is large enough to be perceptible only when sources are within one or two meters of the listener. Results are not dramatically different if one assumes that the ears are separated by 160 deg along the surface of the sphere (rather than diametrically opposite one another). Thus for nearby sources, binaural information should allow listeners to locate sources within a volume around a circle centered on the interaural axis on a "torus of confusion." The volume of the torus of confusion increases as the source approaches the median plane, degenerating to a volume around the median plane in the limit.

This paper presents new results showing the application of polyomino-based subarrays to limited field of view and wideband, wide-angle scanning. This technology can reduce the number of phase controls in arrays used for limited sector coverage or the number of time delay devices for wideband radar or communications, and so can reduce the cost of space-based active arrays. We concentrate on the wideband application. Results are presented by comparing the gain and peak sidelobe results of irregular polyomino subarray-based arrays with those of rectangular subarrays. It is shown that using irregular polyomino subarrays can result in a major decrease in sidelobes while presenting, in most cases, only a few tenths of a dB gain reduction compared to rectangular subarrays.

No abstract

No abstract

No abstract

No abstract

Localization was measured for nearby sources with abrupt or slow rise/fall times in a reverberant space. A recent model of distance perception [A. W. Bronkhorst and T. Houtgast, Nature 397, 517–520 (1999)] suggests that perceived distance is computed from the room impulse response. The model assumes that energy in the onset of the impulse response (primarily from the direct sound, varying with distance) is compared to late energy (primarily from the reverberation, roughly independent of distance). However, other results suggest that subjects are poor at deconvolving transfer function and sound source characteristics [Rakerd et al., J. Acoust. Soc. Am. 106, 2812–2820 (1999)]. Taken together, these results suggest that subjects cannot use the transfer function, but estimate source distance from some statistic closely related to that proposed in the model (e.g., the ratio of initial to late energy in the total waveform at the ear). For impulsive sounds, such a simpler statistic yields results similar to those of the model; however, distance judgments would be significantly degraded for sources with slow onsets. However, subjects were equally good at judging distance, independent of characteristics of the stimulus envelope. [Work supported in part by AFOSR Grant No. F49620-98-1-0108.]

No abstract