A B Pair Spacing - Opinions

[mrsteaks]

Great shot! C414's over the choir? Now for the stoopid question - what are you using for the A B pair arm?

~~~~Mark S.
Pretty Good Recordings

[d_fu]

Originally Posted by mrsteaks

Great shot! C414's over the choir? Now for the stoopid question - what are you using for the A B pair arm?

414s indeed, two B-TL, one B-ULS. The stereo bar is DIY...

[mrsteaks]

I've gathered that most stereo bars are DIY. AEA makes nice ones, but they are pricey. They're also short, IMO. I think they only extend about three feet. Could be wrong, me! Manfrotto makes a nice one, too - affordable, but it too is only three feet.

~~~~~Mark S
Prety Good Recordings

[brubart]

Typical A-B pair spacing for the main pair is 40 to 60 cm. Spacing below 40 cm tends to produce a narrow stereo stage, while spacing above 60 cm tends to produce exaggerated separation. But the spacing for accurate imaging really depends on the angular width of the musical ensemble as seen by the mic pair.

Here's a suggestion. During a rehearsal, set up the A-B pair with a certain mic-to-mic spacing and distance from the ensemble. Record yourself speaking from various positions on stage while announcing your position ("far left", "half left" "center"...). Then play back the recording over speakers to see how accurately the images are localized by that mic spacing.

For example, suppose on playback you hear yourself saying "half left" but the image is close to (or at) the left speaker. That means the mics are too far apart in that situation. Or you hear yourself saying "far right" but the image is half right. That indicates that the mics are too close together.

Hope this helps,
Bruce Bartlett

[mrsteaks]

It helps indeed! 16 to 24 inches.

Thanks, Bruce!

~~~~Mark S.
Pretty Good Recordings

[RobAnderson]

A few weeks ago I promised to write some sort of paper about this, but I have not had time to complete it as yet. One important point, and someone alluded to this earlier with the link to the Williams paper, is that spacing is related to the recording angle, the recording angle is related to source width as seen by the microphone array, which is related to relative distance from the source.

Dickreiter makes this statement in his "Tonmeister Technology" book:

"A pure AB stereophony exists only for microphones whose spacing is small compared to their distance to the sound source. A spacing of from 20 cm to 100 - 150 cm (8" to 40" - 60") is normal. For closer and extended width sound sources one may use a closer spacing, for more distant and narrower ones, a wider spacing." (p.98)

[mrsteaks]

Originally Posted by liuto

Sources can be found here:

Williams: The stereophonic zoom"
http://www.rycote.com/products/pdf/T...nic%20Zoom.pdf

Sengpiel:
http://www.sengpielaudio.com/Laufzei...fMikrbasis.pdf

Schoeps Mikrofonaufsätze (Wuttke):
http://www.schoeps.de/D-2004/PDFs/Mikrofonbuch_Kap1.pdf

Wittek:
Image Assistant 2.0

Best regards
Hermann

Here is an excerpt from the post you were referring to. Hermann was kind enough to provide links. The Williams paper is excellent!

~~~~Mark S.
Pretty Good Recordings