Topic: Distance/config on split omni's

[Belexes]

I want to try and run split omni's for the first time and have 2 stands and 15' of cable.  How far should omni's be split and do you just run them A-B?

TIA.

[sygdwm]

how far back from the pa will you be? id just split them as much as your cables will allow and toe them outside of the stacks.

[John Willett]

The distance apart will depend on the acoustic and what you are doing.

Personally, I tend to have them about 20cm apart for grand piano.

Too far apart and you can ger a "hole in the middle" effect (hence the Decca Tree with a centre mic. as well).

[Brian Skalinder]

Check out Michael Williams' Stereophic Zoom for a graph of the stereophonic recording angle of various split distances.  This should provide a good starting point.  Adjust accordingly depending on the recording environment, i.e. stage / stack width, your location, etc.

[Belexes]

It'll be a downtown concert series with some flown stacks and I'll be FOB.

[Gutbucket]

Warning - while you were typing 4 new replies have been posted. You may wish to review your post.

Can't see the other responses 'till I reply and I typed all this out so I'm posting anyway, appologies if this has been covered..

Depends. You'll find proponents for spacings anywhere between 7" and 30'! The best advice is to try different spacings and see what you like.  Here are some ideas to work with-

At the most basic (as you probably already know)- on playback, wider spacings sound bigger and more spacious and means stereo information to lower frequencies but too wide can sound like everything on-stage is bunched at either speaker leaving a 'hole in the middle'. The simple solution for that problem is to not place the pair so wide.  The more complex traditional solution is to add a third mic in the center and mix it into the left and right channels equally at a lower level.

Historically for orchestra recording, Europeans used closer spacings and American wider ones. 

One approach is to use the Stereo Zoom data-
Williams' 'Stereo Zoom' has charts that apply to omnis. Search for info on Stereo Zoom here or find the paper posted at the Rycote site.  The charts correspond spacing between the mics to the pickup angle (what Williams calls the SRA or Stereo Recording Angle).  Actually you can infer what the spacing for omnis would be from any polar pattern the Stereo Zoom chart - just read across the bottom of the chart where the angle between the mics equals zero (both mics pointing straight ahead).  None of his charts go wider than 50cm spacing for a +- 50deg SRA but you can extrapolate what the spacing would be for narrower SRA angles.  See the omni chart photo attached.

The Stereo Zoom approach only takes into account the effect of mic spacing on the perceived playback angle using a traditional stereo setup with speakers at +-30 degrees.  But it doesn't take into account at all what I consider much more important for the type of recording most of us are doing here. In my experience, varying the spacing between the mics dramatically affects the quality and quantity of the bass, the 'stereo feel' of the midrange, and the 'air' of the high end of the recording.  Getting those things right are much more important to me than perfectly accurate placement of images in the stereo field on playback, especially if most of the sound is coming from two widely spaced FOH stacks! I find it most useful to set-up, put the rig in rec-pause, put the headphones on and listen while adjusting the spacing until it sounds 'right'.  You're manipulating the correlation between the distance between mics and the wavelength of sound at different frequencies.  Some would say that a decision made monitoring with headphones is compromised, but if anything I'd think you'd be prone to err on the side of less spacing than optimal with headphones.  Doing this at outdoor festival type events with etymotic in-ear phones and isolation muffs over that to block as much external sound as possible, I consistently end up with a spacing of around 36-40" (~1m). That spacing has been consistent enough for me at various outdoor fests that I rarely do the adjustment thing anymore, I just fly around 39".  I'll note that with my omni rig I have the option to adjust from coincident to about 72".  I haven't tried going wider than that, but I'm only using one stand.  I've heard great tapes made with 10' or more spacings though.

[boojum]

Warning - while you were typing 4 new replies have been posted. You may wish to review your post.

Can't see the other responses 'till I reply and I typed all this out so I'm posting anyway, appologies if this has been covered..


Historically for orchestra recording, Europeans used closer spacings and American wider ones. 

One approach is to use the Stereo Zoom data-
<snip>
Williams' 'Stereo Zoom' has charts that apply to omnis.
<snip>

Actually Williams cover omnis, cards, hypercards, hypocards and maybe the other card type.  And not to be argumentative but I find the angles and distances he gives work fine for bass for me.  I use his spacings on omnis and cards and get plenty of bass, and actual honest representation of what is in the hall.  I am doing mostly acoustic so it is pretty easy to evaluate that as opposed to rock which can sound like whatever the guy at the soundboard and the band want.  Not all soundmen are created equal.

I am currently doing a lot of MS flanked by a Williams omni array and like the results.  I do zero outside rock concert recording but will be doing some in August as we are having a "festival" out here.  I'll see what I come up with then.

[Gil]

I've actually had luck using the NOS spacing and angle with omnis. I've only tried it indoors and ~3'-5' from the stage. YMMV.

[indietaperwloo]

Talk to illconditioned about split configurations.  He just set up an awesome split rig at the Starlight club in Waterloo, ON as well as the Boathouse in the neighboring Kitchener.
He uses a pair of Beyerdynamic MC930s hung from the ceiling about 15 ft back from the PA and runs XLR over the ceiling back to the soundboard then plugs them into his FR-2LE.  It sounds pretty kick ass too.  Listen to the Islands clip he put up there and you'll see what I mean.

[Gutbucket]

Actually Williams cover omnis, cards, hypercards, hypocards and maybe the other card type. 

Right.. and what I'm getting at is this- Take a look at each of his charts. Even though the slope of the curve changes according to the polar pattern, the bottom of each individual curve intersects the base at the same point for any given SRA angle.  That is to say, if you point the mics perfectly straight ahead (a 0 degree angle between them), it doesn't matter what polar pattern microphone or what Stereo Zoom chart you use, the charts give the same answer in every case. 

The point is that The Stereo Zoom is very useful, especially for directional mics, but it concerns only the placement of sounds in the playback image.  It says nothing about alot of other important aspects that effect the sound of the recording.

For example, using the example above, changing the polar pattern of the microphone and leaving everything else the same (same spacing, 0 degree angle between the mics) will change the sound of the recording.  The sound changes because by changing polar patterns you will be varying the direct/reverberant ratio.. and because different polar patterns have different on-axis responses.. and because the frequency response of each pattern isn't constant off axis.  Yet none of those changes are what I was referring to in my post about how adjusting the spacing affects the sound.

And not to be argumentative but I find the angles and distances he gives work fine for bass for me.  I use his spacings on omnis and cards and get plenty of bass, and actual honest representation of what is in the hall.  I am doing mostly acoustic so it is pretty easy to evaluate that as opposed to rock which can sound like whatever the guy at the soundboard and the band want.  Not all soundmen are created equal.

I don't mean to imply that incorrect spacing would cancel out the bass or make it sound wrong or something.  It's more a matter of noticing that a subtle change in spacing can sound dramatically different (not that either sound is necessarily wrong) and picking whichever sounds better.  I do think that amplified outdoor sound from two widely separated stacks on either side of the stage is a special case and that the effects of mic spacing on both the feel of the bass and also the rest of the spectrum is likely more exaggerated in that case than for acoustic sources.  I suspect that effect might be even more exaggerated for a mono board mix played through those widely separated FOH stacks. 

For non-house amplified acoustic stuff I'd be more likely to use a smaller spacing.. and be alot closer!  The special case of an amplified outdoor festival presents a source that is big and wide like an orchestra.  An old general approach for spaced omnis some took was space them 1/2 as wide as the source width.  Also consider how far back you'll be.  At the FOB spots I record from at festivals, the stacks may be 50 deg apart as viewed from my mics.  That would indicate a spacing of 50cm by the Stereo Zoom.  But the performers on stage take up an angle of only 20 degrees and that puts me right back to right around my typical 39" if you extend Williams' charts.

I've actually had luck using the NOS spacing and angle with omnis. I've only tried it indoors and ~3'-5' from the stage. YMMV.

Generally the closer you get to the source the narrower you'd space the mics (and the wider the recording angle gets).  The Healy method is 7" spacing with 180 degrees between mics and was designed as an onstage technique.  So your experience a few feet form the stage is along that continuum.

I am currently doing a lot of MS flanked by a Williams omni array and like the results.  I do zero outside rock concert recording but will be doing some in August as we are having a "festival" out here.  I'll see what I come up with then.

Are you mixing the mic sources together? If so are you using the omnis just for low end reinforcement or mixing them in full frequency?

[boojum]

Are you mixing the mic sources together? If so are you using the omnis just for low end reinforcement or mixing them in full frequency?

GB - I am mixing the two.  Adding enough of the "room" from the omni's but not too much in my amateur opinion.  The MS are in the center with an omni about 6 or 8 inches on either side, according to Williams charts.  I just did a classical Young Artists performance and when I get it mixed down I will shoot you a sample of the mixed and the same thing unmixed or 100% from each track, if you would like.  It is a small setup this way and quick to set up.  Eargle's wide spacing of the flanking omni's requires two more mic stands and a commotion with the wiring.  This I just put a cheap OnStage mic stand in place and run the four mic cables off to my recorder; done.  Ah lak it.  I am also still evaluating it.

I kept bees for a number of years and every once in a while someone would show up at the beekeepers' meeting with a "new" idea.  Or maybe it was published in one of the two bee journals.  A little research wuold reveal that yes, that idea was around in 1893, proposed by so-and-so, etc, etc.  There is very little new in beekeeping.  I am pretty sure lots of other folks have tried MS with a Williams array and I just do not know about it.  New to me; old to the rest of the world.  If it is a good one I will let you know.  In the meanwhile I can send you the files, I you want and they turn out OK enough I am not ashamed of them.

Cheers.     

[Gutbucket]

It is a small setup this way and quick to set up.  Eargle's wide spacing of the flanking omni's requires two more mic stands and a commotion with the wiring.  This I just put a cheap OnStage mic stand in place and run the four mic cables off to my recorder; done.

So true, it so often comes down to what is simple and doable, despite the theoretical wahoo, doesn't it?

Mixing in your omnis at a lower level may add just enough omni 'space and room' yet still be low enough in level to avoid the comb filtering effects higher up. 

If you want to play with it further you could try low passing the omnis before mixing them in, which should allow you to add more omni without the comb filtering at higher frequencies, or spacing them farther apart which would uncorrelate them enough to avoid comb filtering like Eargle's flanking omnis or ambient room omnis further back in the room.

Wise insight with the bees, my friend and oh so true.  I'm sure many others have thought all these things through already. The only thing working in our favor here is that the history of recording and surround sound in particular is a mere spec on the calendar compared to the history of apiarism.  When I was playing Ultimate Frisbee 20 years ago in college I had friends that went on to play in the world championships 10 years later.  That would never have happened if we were playing football, baseball or basketball.  It's a bit easier to innovative, and perhaps even excel, when you are fortunate to live relatively close to the birth of the sport.. or the technology.

[jlykos]

My own experience running my Gefell omnis is that a 3-4 foot split works best if I am taping from the section or something like that.  I also like to point the omnis directly at the stacks; I know that it doesn't do anything except give me a bit more spacing, but perhaps there is something psychologically that I like about it.  Wider than 4 feet and I get a hole in the middle, but I admit that I do need to experiment more.

[goodcooker]

I have run omnis in NOS and slightly wider/narrower angle configs with good results outdoors

and subcards A-B with 3 to 12 feet spread with varying results. ( I liked around 6 ft the most)

I like the sound pf the wide split, but some people called it the "hole in the middle" sound. YMMV

In the future I  will prob stick to less than 6 feet split.

[mblindsey]

I tried running split omni's for the first time, and I've got some more experimenting to do to get it right.  Anyway, here is an example recorded with a 3 foot split:

http://www.archive.org/details/matisyahu2008-06-24.naiant-xt.flac16

..and, another recording from the same show (same spot) with cards:

http://www.archive.org/details/matisyahu2008-06-24.Flac24

The difference in stereo image is pretty dramatic. 

--Michael

[grayp]

My own experience running my Gefell omnis is that a 3-4 foot split works best if I am taping from the section or something like that.  I also like to point the omnis directly at the stacks; I know that it doesn't do anything except give me a bit more spacing, but perhaps there is something psychologically that I like about it.  Wider than 4 feet and I get a hole in the middle, but I admit that I do need to experiment more.

i agree with this for sure.   ran about a 30ft split at panic this spring and it def had somewhat of a hole in the middle.   did about 4 ft at delfest which came out much much better.   

[Gutbucket]

Seems to be a common theme that alot of us recording stack amplified stuff from the section end up with a 3'-4' spread. Also from a purely practical standpoint, that spacing is easily managed with two festival chairs in between the stands to fortify the encampment. -Or two stands at the edges of a stand clump/stand grove/groove grove/bunch of d00ds tapin'/call it what you will.

[Belexes]

I think I am going to set up at the corners in front of the soundboard.  That should give me about 3-4 feet and hopefully no "hole in the middle" effect. Thanks to the responses so far.