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Spacing and mounting for AB stereo pair? Signal Splitters (HW)
Old 31st August 2008
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jnorman's Avatar
Question Spacing and mounting for AB stereo pair?

some of youse guys use small AB spacing, like 20cm, while others use perhaps 1m. 20cm can easily work on a normal stereo bar on one stand, but 1m spacing requires either two stands or a $5M stereo bar.

my applications are usually a small chamber group, not ususally more than 4 players, or solo piano, or piano and soloist. spaces vary from dead living rooms to large, reverberant churches.

what kind of spacing do you prefer for an AB pair, how do you alter the spacing based on what you are recording, or what kind of space you are in?

how do you normally mount your AB pair? 2 stands, or one stand with spendy stereo bar?

when you use omnis for flanking mics, what kind of spacing do you use? thanks.
Old 31st August 2008
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Corran's Avatar

I actually just started experimenting with A-B setups, usually preferring ORTF due to poor acoustics in the hall I record in most frequently.

I use the Sabra-Som ST4 stereo bar (only about $50) which has a 30cm spacing, and for small chamber stuff it has worked fine. I have an orchestra recording in a couple weeks that it might be too small for, but they have longer bars for sale as well. I plan on probably just angling the mics to get a better spread and see what happens (I'll be running an ORTF pair anyway, the A-B pair will be an experiment).

Don't forget you can make a bar yourself too, which will be much much cheaper. I need to do that myself.
Old 1st September 2008
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just.sounds's Avatar
I use a stereo bar The K&M type costs 15 bucks or so and if it is too small you can attach them to each other for more reach.

20 to 40 cm is optimal enough for all situations. I don't get the a/b setups larger than 1m exept when used as "outriggers". The stereo image has a hole in the middle.
Old 1st September 2008
Gear Addict

I bought the Samba kit and then got a piece of hex rod cut at the local metal yard... for about $5 I now have a 42" bar. Not bad.
Old 1st September 2008
Gear Head

I also extended a shop-bought Sabra Som bar. It works really well. For reference, the replacement hex rod thickness should be 3/8 inches from flat side to flat side. 10mm is a tad too wide and won't fit. My local metal supplier ordered a bar for me. Arrived in within 2 days and cost me £7. Bargain.

Old 1st September 2008
Lives for gear

For all of these, it really depends on the size of the ensemble.

If I'm recording a classical guitar with an A-B pair then I go perhaps 14-18 inches. I rarely record small ensembles with spaced pairs, but the few times I have, I'll go roughly 3 feet wide as a starting point.

Flanking mics are a whole different issue. How does the microphone system work (all the mics put together)? How wide is the image from the center mic? How wide is the ensemble and the performance sound stage? For an ORTF pair, I may go 3 feet on either side of the main pair for a chamer group or I may go 8 feet on either side. Orchestras get their flanking pair at usually about the 2nd row of strings.

You just need to listen and decide what works for the sonic image that you have in your head before you place a single mic.

Old 1st September 2008
You can make custom bars with regular aluminum angle stock from a hardware store, 3/8" rod and/or 3/8" thumbscrews with adapters for 5/8--27 or whatever they call that size of "normal" mic clip threads. I've dismantled and re-mantled quite a few mic holders included with microphones to construct such little devices.

As far as spacing for ensembles, you've got to go on instinct. In a very rough, rule of thumb way-- imagine that the sound everyone is making is visible, it fills the realm around them. The sound is thick and dense right nearby, it's faded and wispy by the time it hits the back wall.

So if that sound makes a 'giant fishbowl' around the players, you place your mics where the 'surface' of that fishbowl would be. If you've only got two microphones, in ORTF front and center. If you've got a few more sets, keep placing them around the group, at wider and wider intervals from the front and center set.

The quick and dirty of it, far as I know.
Old 2nd September 2008
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roonsbane's Avatar
I use A/B whenever I have a great room and an appropriate small ensemble. The two competing issues you have are: If its too wide, the image has a hole in the center and gets washy. If it's too narrow, you get that nasty build up of midrange. To me, the midrange buildup is the more annoying thing, especially since average people rarely really listen from the precise center of the speakers. Never the less, I try and avoid the hole in the center as well. To me, frequency response is paramount. When I walk into a room with music playing, I always immediately hear when a pair of mics is too close or panned in too much from that midrange buildup. I hate that schlock. I know that DPA suggests that most ensembles can be well recorded with their short 40cm $500 bar. In my opinion, that would only work well for a single non full-range instrument or along with wide flanks on larger ensembles. Widths of 2 meters apart generally need a center mic or pair of mics as well on a larger ensemble. My 2 cents.

Old 2nd September 2008
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Don S's Avatar

For a small chamber orchestra or chorus, I like to start at 40 inches. This is using the MK2H. A little less than 40 when using DPA.
The hole must be avoided at all costs. If I do bring them in, I also angle them outward slightly.
Omnis have a high commitment factor, as you're limited to what you can do in post if the recording isn't sounding good because of the spacing.
Old 4th September 2008
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boojum's Avatar
On the subject of AB spacing this fellow is spot on from my own experience:

I am currently using his AB spacing with an XY or MS in the middle. So far it has been good. But I am still fiddling with it. Phase distortion must be watched for. I believe the rough rule of thumb is 6" and up is the max between the AB omni's and the XY-MS setup. I add a bit of the AB for bass and space and it seems to work well.

As usual, YMMV.
Old 4th September 2008
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sonare's Avatar
Originally Posted by jnorman View Post
my applications are usually a small chamber group, not ususally more than 4 players, or solo piano, or piano and soloist. spaces vary from dead living rooms to large, reverberant churches.
Except for rare occasions I will use a M-B Jecklin disc in these situations because of the imaging and the ability to get in close without it sounding like an x-ray.

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