Spaced omni's are less forgiving when it comes to mic placement. Audience noise is more apparent. Proper imaging is more difficult, especially if you have different sized ensembles performing during the coarse of a concert. But excellent depth and spaciousness are the reward.

A starting point would be to space the mics approximately one third the width of the ensemble, then tweak by ear. The omni's should be assigned (panned) hard left and right.

Given those variables, and being restricted to one immovable setup, I'd be inclined to keep your spacing no wider than 4 feet max. Experiment in advance if possible ... that's always the best solution. Spacing does NOT have to be really wide in any A-B application, really. Check out the DPA website for more info on this.

Also, if you are doing only two channels and you have a good 2-ch outboard pre, I would pipe my signal straight through there and bypass the mixer.

Cheers!
Mike

Building on what's been said so far, I think I would approach the problem from two angles:

1. If two mics is your limit AND you will not be able to adjust mic position between ensembles, then I would opt for ORTF. Mic placement is just too critical with omni's to capture proper imaging and ensemble balance, IMO.

2. If one must tolerate a one-time-set-up static mic placement then I would prefer four mics: ORTF center main pair with a pair of omni outriggers out wide. From ensemble to ensemble you could blend different amounts of outriggers with the mains. I think this would be a nice compromise betwixt varied ensemble balances, fullness of sound, and avoiding the unwanted realities of a live performance.

Thank you for your suggestions. Zilla, I may try the ORTF-Omni Outrigger suggestion next concert. (Drat, it means adding two mic stands to my supposedly portable rig.)

I’m curious as to why DPA suggests a spacing of 40cm to 60cm (approx. 16” to 24”) for Omni microphones in A-B configuration when I often see much wider spacing used in practice. Is this for recording single instruments? Certainly, were I to space the microphones at 1/3 the width of the ensemble that I record, the spacing would be more along the lines of 3 to 5 feet (approx. 100cm to 150cm).

-- James

Zilla has brought up pretty much the same points I would have... In my usual 3-point rig, I usually use a Blumlein pair instead of ORTF, though...

One of the major issues that you run into with spaced omnis is the image bouncing from side to side. Because of the space involved, it tends to exagerate the feelings of distance so a small movement will swing from one speaker to the other. It can be very bothersome on a small ensemble.

Spaced omnis can work well when you have larger ensembles and instruments that won't move (like solo piano).

--Ben

JimboJ wrote: I’m curious as to why DPA suggests a spacing of 40cm to 60cm (approx. 16” to 24”) ... were I to space the microphones at 1/3 the width of the ensemble that I record, the spacing would be more along the lines of 3 to 5 feet

I don't know why they suggest that close of a spacing. In practice I have never had a spaced main pair closer than 30", with 3-4 feet being typical. For really big ensembles, they can go even twice that width, depending on the acoustics.

The physics behind Coincident and Near-Coincident techniques are such that they provide relatively predictable results. Spaced omni's are flapping out in the breeze of chaos. So don't take that 1/3-width recommendation as gospel, only a good starting point. Then listen and use Zen, the Force, or anything else at your disposal to coax the mics into their proper spacing. Set-up usually becomes quite a dance.

It's interesting to see a discussion of A-B pair spacing. I lived for a while in the US, and I noticed that spacings of the kind you guys are discussing, in the order of three, four or more feet, are quite normal on that side of the pond. Over here, and ime in Europe generally, the 400-700mm spacing is more commonly used. I've come to regard the wide spacings and/or three mics in a straight line setup as "American", whilst the closer spaced pair and Decca Tree are more British/European. It'd be very unusual to see for example, a UK based engineer setting up a wide spaced pair, straight line, or following the "rule of thirds" approach.

I wouldn't say that either was better than the other, both undoubtedly deliver great results in the right circumstances. It's just curious that engineers on both sides of the pond use the same gear on the same kind of music in the same kinds of acoustic, yet they approach it so differently. I wonder why.

An interesting observation.

It may be differences in cultural aesthetic sensibilities. Or maybe because Europeans have many more amazing acoustics available to record in, while us Yanks are struggling to get spaciousness from our tee-pee venues.

Zilla wrote: ... Europeans have many more amazing acoustics available to record in, while us Yanks are struggling to get spaciousness from our tee-pee venues.

Hee Hee - so true. Despite all of our wonderous technologies built into fantastic halls within the past 20 years - nothing compares to the centuries old Concertgebouw.

Not that I can really add that much to all the great info above, but I'll at least chime in with some agreement.

My personal thought on AB mic'ing is simple. A 2 channel omni only recording is the test of one's culmination of knowledge of acoustics and orchestral performance. I cheat and use multiple mics - 3, 4 or 6 often. (Though I've been known to use only the main pair when I can get them sounding oh so glorious.)

In your case, with changing ensembles, I don't think it to be possible. You would want to go with something stable like ORTF or XY. Neither of these would give you your absolute best sound, but they'll be far more predictable and still give you decent/usable sounds.

I will also agree that, if using only 2 omnis, wide spacing is preferred. (At least on this side of the pond.) A lot of people will argue the "hole in the middle" complaint. Well, it certainly is possible to get the hole in the middle, but often I find this has as much to do with distance to the ensemble and height as it does to do with spacing between mics.

Because all these variables are SO volatile in AB, your best bet is to try a nice coincident/near-coincident technique and then later, try using AB with outriggers in a multi-track set-up. If you can get your main pair (the true "AB" pair) sounding fantastic, then you won't even need your outriggers. But, if it sounds a little wierd without them, then you need more practice (or the higher track count. :wink: )

J.

Sorry to inject some ignorance into an otherwise learned conversation, but I 'read' (which is significantly different from: ' I have experienced' ) that two mics should be 3 times as far away from each other as from the source, so shouldn't they be far apart?

That rule would indicate that if the mics are 30" apart, one of them is basically sitting on the lap of the oboe player...

Confused
Keith

took-the-red-pill wrote: Sorry to inject some ignorance into an otherwise learned conversation, but I 'read' (which is significantly different from: ' I have experienced' ) that two mics should be 3 times as far away from each other as from the source, so shouldn't they be far apart?

Keith, I will try to give an answer. This is indeed a rule of thumb used in recording. But it goes mainly with a different recording setup.

Here we want the two, or more mics, to blend the instruments together into a coherent sound. We want each mic to "listen" to a part of all the instruments.

The 3:1 rule is mostly applicable when you want to multitrack each instrument and have separation between the different instruments, each on its own track. In this type of work, we want each mic to only listen to one single instrument.

When using the 3:1 rule, one of the things you want to avoid is phase issues, which occurs when several mics hears the same source and they later are mixed together. The rule makes sure that the other sources are low enough to not create phasing problems. In a classical multi recording, you may end up with phase issues. The "classical" mic setups, say ORTF, build on experience on how to change the problem into useful information, for ORTF it is part of how the stereo image is created.

The difference in how you work, is one of the reason why omni mics are less common in pop/rock recording.

Gunnar.