The Magic in 2-Channel Sound Reproduction - Why is it so Rarely Heard?

Authors

  • Siegfried Linkwitz Linkwitz Lab, Corte Madera, California, USA

DOI:

https://doi.org/10.15377/2409-9821.2015.02.02.2

Keywords:

Sound reproduction, Loudspeaker, Room, Perception, Magic, Aural scene, Radiation pattern, Constant directivity, LX521, LXmini

Abstract

Hearing, finding the direction, distance and significance of a source of sound in various acoustic environments, is a survival mechanism in the evolution of living organisms. Hearing two strongly correlated sources of sound, either from earphones or two loudspeakers, is an unnatural phenomenon, from which the ear-brain apparatus is asked to draw an illusion of reality. Misleading cues must be eliminated from the sound presentation for the illusion to happen convincingly. In the case of earphone presentation, which typically suffers from a high degree of distance distortion, i.e. distance foreshortening, the ear signals must change with head movement to externalize the illusion. In the case of loudspeaker presentation there is already the distance between listener and speakers, which typically is perceived as the minimum distance to the illusionary aural scene or phantom scene. But that scene is usually hard bounded by the speakers, which are recognized as such by the ear-brain perceptual apparatus. One or the other speaker is preferred as the source, when the listener moves a short distance away laterally from the "sweet spot". In a reverberant room, where the listener not only hears the direct sound but also the reflected sound, i.e. the off-axis radiated sound, the ear-brain perceptual apparatus must be allowed to withdraw attention from room and speakers and focus attention upon the direct sound to create a convincing illusion of the reproduced acoustic event. For this to happen misleading perceptual cues must be eliminated. The speakers must be placed so that reflections are delayed relative to the direct sound. The speakers must be free from spurious resonant radiation and their off-axis radiation must follow their on-axis frequency response for the reverberant sound to be neutral. The polar radiation pattern must be essentially either omni-directional, cardioid or dipolar, aiming for constant directivity. The speakers must be acoustically small, yet capable of realistic volume levels at low non-linear distortion. Two prototype speakers and the evolution of their radiation pattern design will be discussed: a full-range, acoustically small dipole and a hybrid, omni-cardioid-dipole design. Either speaker is capable of disappearing from perception and rendering an aural scene in a reverberant room that is like a magic act.

References

Bregman S. Auditory Scene Analysis - The Perceptual Organization of Sound. The MIT Press 1999.

Beranek LL and Mellow TJ. Acoustics - Sound Fields and Transducers. Elsevier Academic Press 2012.

Meyer J. Acoustics and the Performance of Music, Springer 2009. http://dx.doi.org/10.1007/978-0-387-09517-2

Rumsey F. Spatial Audio, Focal Press 2005.

Wittek H. Image Assistant, JAVA applet for determining the, "Stereo Recording Angle", www.hauptmikrofon.de.

SCHOEPS Mikrofone. Showroom, www.schoeps.de/en/applications/showroom.

Rakert WM. Hartmann, "Localization of sound in rooms. V. Binaural coherence and human sensitivity to interaural time differences in noise". J Acoust Soc Am 2010; 128(5).

Linkwitz S. A Model for Rendering Stereo Signals in the ITDRange of Hearing, 133rd AES Convention, San Francisco 2012, Preprint 8713.

Benjamin E. An experimental Verification of Localization in Two-Channel Stereo, 121st AES Convention, San Francisco 2006, Preprint 6968.

Blauert J. Spatial Hearing. The MIT Press 1997.

Toole FE. Sound Reproduction. Focal Press 2008.

Damaske P. Acoustics and Hearing. Springer 2008.

Linkwitz S. Room Reflections Misunderstood?. 123rd AES Convention. New York October 2007, Preprint 7162.

Kuttruff H. Room Acoustics. John Wiley and Sons 1973. http://dx.doi.org/10.4324/9780203186237

http://www.linkwitzlab.com/rooms.htm

Linkwitz S. Investigation of Sound Quality Differences between Monopolar and Dipolar Woofers in Small Rooms. 105th AES Convention, San Francisco 1998 Preprint 4786.

The Absolute Sound's Illustrated History of High-End Audio. Volume 1: Loudspeakers, Edited by Robert Harley, Next screen, Austin, Texas, 2013.

http://www.linkwitzlab.com/LX521/Description.htm

http://www.linkwitzlab.com/LXmini/Design.htm

Downloads

Published

2015-12-31

How to Cite

1.
Siegfried Linkwitz. The Magic in 2-Channel Sound Reproduction - Why is it so Rarely Heard?. Int. J. Archit. Eng. Technol. [Internet]. 2015Dec.31 [cited 2021Sep.25];2(2):113-26. Available from: https://www.avantipublishers.com/jms/index.php/ijaet/article/view/378

Issue

Section

Articles