OCT-
I think the OCT also looks pretty cool.
Love it outside where it's a primary basis of my current outdoor oddball setup. Fantastically good imaging using 3 front speakers, and a really cool intense forward "presence" when mixed in to 2-ch stereo. The 180 degree sideways-opposed facing supercards optimally reduce crosstalk reducing the need for a super-wide Left/Right spacing. Because of that one can get away with spacings normally used with just two omnis of a just meter or less. Just be careful indoors where those mics may be facing a reflective wall. I've had good results indoors from the sweet spot a few times but have not used it indoors extensively. It was less good onstage for jazz trios in a small reflective room, where Williams 3-mic arrays using supercards pointing more at the on-stage sources worked better (sort of like a mini directional Decca tree arrangement). I've considered increasing the L/R supercardioid spacing and angling them forward at something like a 90 degree angle between mics indoors to compensate, but haven't tried that extensively.
For that OCT layout . . . what does "omni directional" mean?
Also, on the left side we have two mics with complementary 100Hz high and low pass filters being summed. No such setup on the right side, just the "omni directional" mic. The asymmetry puzzles me. Perhaps that arrangement on the left side creates a single "omni directional" mic and we see it simplified on the right. It baffles science.
Same on both sides, just shown on the left. The omnis are intended to extend the bass response of the supercards, arranged coincident with them and low passed at the point where the supers loose sensitivity.
I make a few oddball variants on standard OCT-
1) I use a center supercard instead of a carioid. That increases center mic isolation from audience noise and room sound (more SBD-like direct sound from the center mic), and theoretically allows for a slightly narrower L/R supercard spacing to produce the same SRA linking. Of these two aspects, the increased forward directivity thing with less side pickup is the most important aspect for audience taper positions by far.
2)I like the omnis spaced twice as wide (about 1.5 to 2meters), and don't low pass them. That makes for more involving wide-spaced omni stereo bass which I dig, and a more open pickup of ambient content. I EQ and mix the omnis in to taste which contours their mid and high frequency contribution, EQing for both bass timbre and appropriate ambient air and room sound. This wider spacing is difficult to achieve on a single stand with typical omnis, but is achievable using lightweight miniature mics. The supercards and omnis are all in one plane so they can be arranged along one (long) bar. For surround use I send the mids and highs from the wide omnis to the surround channels.
3) I add a backward facing center cardioid or supercardioid. As mentioned above I like to have mix control over venue and audience ambience and a rear facing directional mic allows for that (the omnis pickup fantastically good ambience, but too much direct sound to provide really good mix control over the ambient balance). I figure a cardioid here is optimal for achieving maximum rejection of the direct sound arriving from the front, but the supercards I've used for this seem to work just as well if not better, so I now use identical miniature supercards all around for Left/Right/Center/Rear. This keeps timbre the same all around and also makes the entire 6-mic array completely front/back symmetrical, producing both front and rear facing OCT arrays.
[edit]- the
OCT surround array specifies two rear facing cardioids, spaced apart and a bit further back than the single rear-facing mic I'm using. That's probably a better setup for both 5-channel and 2-channel mixdowns as long as one is capable of dedicating two recording channels to backwards facing mics, because it spreads that ambient surround content in the playback image out to the sides making it less likely to conflict with the forward facing center channel information. In my oddball variant, in addition to using the omnis to provide stereo bass extension below the limits of the OCT supercards, the wider-spacing of the omnis than the supercards (the omnis are essentially spaced twice as wide) allows the omnis to serve as surround channels in combination with the single rear-facing mic. The spacing between L/R supercards and L/R omnis is essentially insignificant at low frequencies where the wavelengths in question are long and the omnis are meant to extend the frequency response of the supercards, but significant at shorter wavelengths where the increased spacing serves to decorrelate the omni mids and highs (routed to the surround channels or mixed in to 2-channel as ambience) from the mids and highs from the L/R supercardioids. So the omnis end up serving dual purpose as bass extension and as ambience/surround channels, and arguably do a better job in both rolls in this configuration as well as being more easily managed since they are positioned further out along along the same telescopic bar(s) as the L/R supercards.