Vertical localization and image size effects in loudspeaker reproduction

Abstract

The apparent elevation and size of auditory images from hidden loudspeakers is examined in two experiments. In the first, band-limited and broadband noise stimuli were presented from loudspeakers in a vertical array. Low frequency stimuli were heard as lower in space than equivalent high frequency stimuli. Loud and low frequency stimuli were judged larger than quiet and high frequency stimuli. The second experiment tested whether the localization difference between low and high frequency components was maintained when presented simultaneously – subjects adjusted the height of a woofer and tweeter, so that both seemed to come from a specified height. In all conditions, the woofer was positioned above the tweeter, showing that the effect can be maintained for simultaneous stimuli. INTRODUCTION Compared with the horizontal plane, contemporary audio systems pay little regard to the vertical dimension of auditory space. This bias comes partly from the greater robustness of lateralization cues than median plane cues in auditory localization. With multi-way loudspeakers and the widespread adoption of subwoofers in domestic sound reproduction systems, the frequency spectrum is often distributed across the vertical dimension by coincidence, instead of having vertically distributed channels designed to control the vertical image location. This paper considers, at least in a preliminary way, how the vertical localization and image spread of auditory images might be influenced by the vertical loudspeaker array design. 1 BACKGROUND 1.1 ‘Height’ and Sound The use of the terms ‘high’ and ‘low’ to refer to frequencies and pitches is a pervasive metaphor, the basis of which has been the matter of significant debate. Stumpf’s [1] observations of the association in the Nineteenth Century sparked explorations in music theory and psychoacoustics on whether the metaphor is inevitable, and also whether it has a perceptual basis. The metaphor is now part of standard jargon of AES 24th International Conference on Multichannel Audio acoustics (in describing frequency