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AES

Audio Engineering Society

Presented at the 99th Convention
October 6-9, 1995 , New York, NY

 

AMBIOPHONICS

The Synthesis of Concert-Hall Sound Fields in the Home

by Ralph Glasgal

ABSTRACT

The completion and testing of the first full-scale version of the Ambiophonics Home Concert Hall has demonstrated that the Ambiophonics sound reproducing technique is a worthy successor to both stereophonic or surround-sound listening configurations in that it can consistently generate a "You Are There": concert, opera, or pop sound field from standard LPs or CDs that the ear-brain system will accept as real. The Ambiophonics method combines an exploitation of under-appreciated psychoacoustic principles with the basic rules of good musical performance-space design to create believable concert-hall sound fields in dedicated home-listening rooms. Using readily available loudspeakers and electronics, Ambiophonics moves the listener into the same space as the performers, by accommodating to individual pinna characteristics, minimizing interaural correlation at the listening positions, abandoning the traditional stereo loudspeaker equilateral triangle, generating early reflections and reverberant fields electronically, eliminating front-loudspeaker crosstalk and reducing the home music theatre wideband reverberation time to less than .2 seconds.

 

 

0.0 INTRODUCTION

The Stereophonic method of reproducing two-channel recordings has had a run of some 65 years since 1931, when Alan Dower Blumlein applied for his patent, though he did not actually use the word "stereophonic." He was primarily concerned with duplicating the frontal directional effects of binaural sound in theaters, using loudspeakers instead of headphones. However, he knew, even in 1931, that his stereophonic technology was flawed. He wrote, "It can be shown, however, that phase differences necessary at the ears for low-frequency directional sensation are not produced solely by phase differences at two loudspeakers both of which communicate with both ears [emphasis mine] but that intensity differences at the speakers are necessary to give an effect of phase difference." While I find Blumlein or his patent attorney's writing style unusually obtuse, his compulsive interpolation in this paragraph of a seeming non sequitur concerning what we now call interaural or stereophonic crosstalk is difficult to justify on technical grounds. Indeed the problems resulting from the fact that each loudspeaker communicates with both ears is not referred to or discussed anywhere else in the patent document. I believe that Blumlein wanted his knowledgeable posterity to know that he knew that his model for stereo sound reproduction was flawed, but he did not wish to vitiate his patent with negative comments. Also because the illusion he could create using even this imperfect technology was so vivid and exciting, compared to monophonic reproduction, he must have felt that any theoretical shortcomings could be safely overlooked. Indeed, Blumlein's basic method has been the two-channel reproduction standard for over sixty-four years. Now, it even has a new lease on life in the form of surround sound, where the left, right, and center front loudspeakers rely on the Blumlein method to generate frontal sound images. However, as we shall show, the time is ripe to replace stereophonics with Ambiophonics, and to correct the many flaws in stereo systems other than loudspeaker crosstalk.

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