"Toole-ing" down the Imaging Road

[HornEd]

Here are some words from one of the most respected pros in the sound business... his fans include BobG, TV, and me (HornEd)

Floyd Toole on Audio Imaging: Stereo vs. Multichannel

''Imaging' has several dimensions, and a thorough discussion would be an article in itself. At the lowest level, there is the position in space of the voice and instruments of music, and sound effects in movies. Absolute precision is not normally a requirement in this respect, assuming that you knew what you should be hearing, which, for the most part, we don't. More important for most of us, is the sense of space, air and envelopment that persuades us that we are not in our small(ish) listening rooms.

"Two-channel stereo is a directionally and spatially deprived medium. In stereo systems there are two 'hard' locations (the speakers) and a number of 'phantom' locations between the speakers (only for the person in the stereo seat). Multichannel audio adds a hard centre, removing the centre-image comb filter that we have listened through all these years. Now, in addition to better fidelity, we can move around the room and the featured artist stays put. The two or more surround channels are there to provide the sense of space, to add some dramatic localised sounds in films, plus some 'artistic' effects in music.

"As for the hardware, multidirectional surround speakers (e.g. dipoles) can add to the sense of space, but detract from the directional impressions. Direct radiating speakers do the reverse. Placing the surround speakers at the sides and adding two more derived (eg Lexicon Logic 7) channels in the rear provides the most satisfying solution.'

The Golden Rule: It may seem obvious, but the golden rule when fine-tuning your system is to experiment. Imagine sound waves travelling in straight lines and focus speakers toward the seating area. Try various speaker placements, both near and far from walls. Every movement will cause a reaction. Tweak and enjoy!"

Excerpt from an interview of Dr. Floyd Toole by Melanie Garrett, Home Cinema Choice, July 2001. Dr Floyd E. Toole is both the Corporate Vice President of Acoustical Engineering for Harman International Industries in Northridge, California, and Senior Vice President of Acoustical Engineering for the Harman Consumer Group. He attended the Imperial College of Science and Technology in London, where he received a Ph.D. for a thesis on sound localisation, including original research on the perception of direction in normal hearing and in stereophony. After graduating in 1965, he joined the National Research Council of Canada, expanding his interests into the complicated interactions of room acoustics and loudspeakers. His learned publications have won various awards from the Audio Engineering Society (AES).

This message has been edited by HornEd on 02-22-2002 at 10:25 PM