Whenever possible I like to use stereo FOH with center channel for live sound reinforcement. I place the left and right main loudspeakers farther appart than usual to increase the "sweet spot" listening area and fill any perceived "hole in the middle" with a center channel. This configuration allows accurate amplitude panning for positionaing of sound sources but most importantly, it allows me to use stereo microphone techniuqes on acoustic instruments.
In live situations, a popular style with bluegrass performers is the single microphone technique. Here the group is gathered in a simi-circle around one high quality microphone, located at about upper chest level. Each performer then moves in on the mic for their solos. This works well with a mono system (even though the mic is not located optimally for either voice or instruments). However with stereo processing the sound becomes infinately better and a higher degree of control can be attained. To acheive this I like to use a variant of a near-coincident process with the FOH mentioned above.

Studies have shown ORTF groupings produce the most accurate acoustic image when widly spaced loudspeakers are used. ORTF is where two cardioid microphones are spaced 6.75" (17 cm) and splayed 110 degrees, one panned fully left, the other fully right. I use this setup in combination with a third microphone. All three are mounted on one stand. The ORTF pair is positioned lower, at about the level of the instruments. The single mic is positioned between the ORTF pair but higher, just below the level of the voices. It is panned center.

There are some advantages to this arrangement:

Stereo: Acoustically generated stereo imaging is stunning, especially when heard live through a great system. In comparison mono sounds one-dimensional.

Optimization of location: The microphones are placed closer to their respective sources. Loss of potential gain before feedback by using more microphones is compensated for by closer proximity and better directivity.

Optimization of microphone type: Microphone types more ideally suited for each purpose can be utelized. For instruments small or medium diaphragm condenser microphones can be used as the ORTF pair and a large diaphragm condenser with a presence peak can be used for voice.

Control: With a single microphone control is limited to EQ and compression. In addition this technique allows image control by panning each ORTF microphone less fully. Also a degree of mix control is possible by adjusting relative levels of voice and instrument microphones.
As a further options, instead of FOH center being a left/right summation, it could be a dedicated channel of the voice microphone. Conversley, in venues with a center cluster, the ORTF pair could go to dedicated left/right loudspeakers brought in for the event. With a little imagination and some experimation, truely amazing results can be achieved.

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Here are a few links with background on some of these topics:

The Single-Mic Technique by Bruce Bartlett.

Stereo Microphone Techniques Explained (part 1), by Hugh Robjohns, Sound On Sound magazine.

Stereo Microphone Techniques Explained (part 2), by Hugh Robjohns, Sound On Sound magazine.

STEREO MICROPHONE TECHNIQUES by Bruce Bartlett.

Office de Radiodiffusion Télévision Française(ORTF) from Wikipedia.

Microphone - Definition, Meaning, Explanation by akademie.de.

Microphone theory links by Han-Kwang Nienhuys.

Addendum: As far as I know, this particular arrangement has not yet been documented, though I'm sure some have used it. In sharing it with you I ask only one or two things in return; remember where you first heard about it and place a link to this site.

Copyright © 2005 Anton Niedersteiner. All rights reserved.