Six foot (2m) omni spacing with center and rearward facing cardioids-
Photos attached below of the setup I ran at Magnolia Fest on the Suwannee last month. I often run four spaced omnis at this festival in sort of a four point decca tree, so this year I substituted forward and back facing cardioids for the center and back omnis. By pointing one cardioid forward and the other backwards I intentionally sacrificed the ability to use the two cardioids alone as a typical stereo pair. I also spaced the omnis a little over 6 feet (2 meters) which is more than I would if I was using them alone for stereo. The entire idea was to give up the ability to use one pair or the other alone, and instead optimize the combination of them.
The cardioids were full body Microtech Gefell M94/MV692, placed as close as possible on the center line and angled 180 degrees apart facing directly forward and rearwards (capsules spaced ~13"). The omnis were DPA 4061 omnis. This was intended for use as 3 channel L/C/R stereo (excluding or mixing in the backward facing mic), 4 or 5 channel surround, or for mixing all four channels down to 2 channel stereo.
I wanted to do this for a few reasons, some sound related some simply practical:
1) practical issue- less spacing required between the cardioids verses omnis means no telescopic antennas overhanging the 'isle' between rows of folding chairs at this outdoor amphitheater. Makes for a more compact setup with less possibility of problems if someone parades by with banner, some giant costume head or something. There is less practical problems with wide spacing the L/R pair along the length of the rows.
2) sonic issue- I wanted more forward bias (stage focus) in the center channel, with sources to the sides and rear less represented in that channel.
3) sonic issue- I wanted more level difference rather than time difference between the Center and Rear (surround) channels.
4) practical and sonic issue- I wanted more time difference in between Left and Right omnis with the addition of a center mic.
5) sonic issue- the M94 Gefell cardioids have a rolled off low end response and a more prominent high frequency response. I felt this would work really well mixed to center (or to a dedicated center speaker) in combination with the more bass heavy spaced L/R omnis both in frequency response and in spatial distribution on playback (mids/highs biased slightly towards the center, low bass biased to Left/Right)
2) through 4) above work into my current thinking on stereo and surround recording which is that I generally want more time stereo information in the Left/Right axis and level difference in the Front/Back axis.
Haven’t had a chance to do much with the files yet, but listening back it worked astoundingly well and I plan to do more like this. Somewhat surprisingly the patch I gave out of the R44 to the M10 of another taper here also sounded very good even though the center cardioid was routed hard Left and the back facing one hard Right due to the lack of panning ability on the R44’s outputs, and the levels of the mix with the omnis wasn’t dialed in optimally. I expected that patch to have more of a left side bias with the center mic panned to that side and the audience facing rear mic to the other, but it sounded big open and clear.
I’m going to do something similar, just on a smaller scale for Bear Creek this weekend, narrowing the A-B spread to 3’ and replacing the full sized Gefells with small AT cardioids for a stage-lip/way-FOB rig that is more lightweight, compact, and has lower visible impact.
Full extension with 6 foot spacing on the L/R omnis-
Detail showing side-by side cardioid mounting on the diagonal mic bar to accommodate the mic stand, give equal weight balance, and to keep the Gefells under umbrella if required. Also shown is the support wire which hooks under the telescopic arms to support them without sagging at full extension-
With the arms telescoped in for a 3’ total omni spacing-