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Author Topic: Omnis arranged at 180 degrees  (Read 1158 times)

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Offline jagraham

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Omnis arranged at 180 degrees
« on: January 28, 2018, 06:39:49 PM »
Anyone tape much with omnis arranged at 180 degrees? A taping friend suggested it a while back and I've tried it at a couple shows, one at the board and one up front 5' back from the stack, and I think they came out pretty good. This setup isn't something I see too frequently so I was curious what others on the TS thought of the method, and if you had any specific suggestions I would love to hear them. Seems like a good option for stack taping, and I haven't tried onstage yet but I'd imagine it would work well.

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Offline Hypnocracy

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Re: Omnis arranged at 180 degrees
« Reply #1 on: January 28, 2018, 08:08:58 PM »
This works for Large Diameter microphones...and has been called the "Healy Pattern" because he had two LD's mounted in front of him at the SNB back in the Grateful Dead days...The Polar pattern of a large Omni is not directional at the Lower frequency's but is directional at higher frequency's (somewhat at mids and more so the higher you go).

If you are using Small Diameter or Pinpoint Omni you would be better off spacing them 36" apart for a stereo image. These microphones are much less directional across the whole spectrum.
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Offline aaronji

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Re: Omnis arranged at 180 degrees
« Reply #2 on: January 30, 2018, 08:11:10 AM »
^ Even SDC omnis get fairly directional at higher frequencies.  I find that the 180 degree angle audibly impacts the image and is particularly useful when you can't space them as far as you might like for time-of-arrival differences.

Offline Gutbucket

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Re: Omnis arranged at 180 degrees
« Reply #3 on: January 30, 2018, 11:45:38 AM »
It's an ambient sound recording technique, that is to say it will sound natural and pickup the sound from all around as heard from that location, which is probably why Healy used it (not spaced very widely) in his Ultramatrix mixes for audience and hall pickup, and apparently onstage as well for a while to feed the band's in-ear monitors when they first started using them. 

The 180 degree angle introduces some level differences between channels at high frequencies.  How how low into the treble range that goes is determined by the size of the diaphragm and/or microphone housing.  As Aaron mentions, that can be a useful technique for tapers when they aren't otherwise able to space a pair of SDC omnis as wide as they might otherwise prefer.  Likewise, it can be helpful when using another microphone or pair of microphones in the center between spaced omnis with the intend of mixing them together, by way of creating a bit more signal difference to help reduce phase interaction, at least within that small frequency range.

Conceptually this is sort of like a very tiny Jecklin Disk which is only effective at the highest frequencies.  You can lower the frequency above which the level difference becomes apparent by placing a baffle between the omnis.  The larger the mic housing, the larger the baffle, the lower the corner frequency where this directionality begins to occur.

LDCs behave somewhat oddly and less predictably. A true pressure-omni LDC would exhibit such directionality to slightly lower frequency based on its larger housing (exhibiting more directionality up top) yet those are rare.  Most LDC omnis are electrically switched opposing diaphragm mics and will exhibit this high-frequency directionality in both the forward and aft directions, producing a sort of ragged figure-8 pickup pattern in their uppermost range.
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Offline goodcooker

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Re: Omnis arranged at 180 degrees
« Reply #4 on: January 30, 2018, 12:18:31 PM »

I did this technique several times with my SP C4 omnis outdoors at festivals where I felt like experimenting. I spaced them around 12 inches apart and 180 degrees. I found that closer was better and the playback sounded much better on headphones than on speakers (same thing I've discovered with HRTF). Oddly enough I didn't feel the need to apply the mid and high EQ curve that I usually added to my outdoor omni recordings. Even though theoretically SDC omnis are more directional at high frequencies and I had the mics facing away from the sound source the recordings turned out surprisingly bright and clear.
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Re: Omnis arranged at 180 degrees
« Reply #5 on: January 30, 2018, 01:28:27 PM »
I think that the "Healy Method" is technically a pair of omni's spaced 17cm and angled at 180* (horizontal to sound source).
It's been a while, but I've done it a handful of times in the past with good results IMO.
Experimenting with omni's is pretty interesting!
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Offline Limit35

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Re: Omnis arranged at 180 degrees
« Reply #6 on: January 31, 2018, 12:07:17 AM »
I've stealthed small omnis 180*/90* off axis approximately 8" apart a few times, it was convenient and stealthy. I liked the sound, but it obviously wasn't the best use for the mics, ver. 1 Naiant X-Xs sound good 1.3 m or greater in my opinion where they get a good spaciousness and bass punch. When I run one meter or greater I always have the omnis 180*/90* off axis due to my setup. Since they are small it is easy to mount that way, the old Naiant omnis I mount forward or up because they need SDC style clips. I have never noticed a difference in angle. The CP-2 omni caps I have seem pretty directional for some reason. I have never tried 180*/90* off axis with those yet, it may be interesting with a card center now that I think about it.

Offline DSatz

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Re: Omnis arranged at 180 degrees
« Reply #7 on: January 31, 2018, 10:33:44 AM »
When I was first learning to record, the usual recipe for setting up a pair of omni microphones was to take the full stage width, then place the mikes at the 1/3 and 2/3 points along the front of it. That often meant that the mikes would be 10 feet apart or more. That creates a stereo image with a "hole in the middle" and "swimmy" localization in general. People might put up with those problems, or not perceive them; not everyone cares very much about localization.

Meanwhile over in Europe, the typical usage of omnis was quite different: They were often placed with anywhere from one meter to half a meter between the mikes. Any Americans who saw a setup like that might assume that there would be no "stereo separation" in the resulting recording, but such was not the case.

The thing is, if distance between your two omnis is only a few inches or less, the resulting recording will be essentially mono in the bass. And that means that you're missing one of the main pleasures that an "A/B" recording can offer, which is spaciousness. It comes mainly from low-frequency energy that isn't strongly "correlated" (highly similar from moment to moment) between the two channels. You will be able to localize to a surprising extent, especially if you listen through headphones, but the feeling of immersion in a live space will be absent.

Nowadays there are much better options available: small, single-diaphragm condenser microphones with patterns between omni and cardioid, and very smooth all-around response. These microphones can make beautiful, spacious stereo recordings (like omnis) with stable stereo imaging (like directional microphones) in a way that is simply not possible with omnis or ordinary directional microphones--and they can do this with spacings even less than the typical "small A/B" approach. These are still mostly higher-end microphones (Schoeps, Neumann, Microtech Gefell) but I think in time there will be good-sounding, lower-cost alternatives as well.

P.S.: If you absolutely must use a pair of omnis in this way, consider getting sphere attachments for them, which will emphasize their midrange directivity. See for example http://schoeps.de/en/products/ka40 (please visit the "graphics" page to see the effect).
« Last Edit: February 07, 2018, 09:38:04 AM by DSatz »
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