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Author Topic: Maximum “acceptable” vertical spacing for near coincident configurations  (Read 727 times)

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Offline ycoop

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My current mic bar doesn’t allow me to run full bodied mics in DIN or ORTF without the XLR plugs overlapping (I see the advantage of active cables now ;)). I can solve this by flipping one of the 5/8” threaded connectors upside down to introduce vertical spacing (see attachment).  I know most custom mounts have a slight vertical offset which doesn’t noticeably introduce any issues. I know I can purchase a small extender to elevate one of the shockmounts, but I’m taping Phish in Tahoe on Tuesday and don’t have time to purchase one beforehand.

How wide of a vertical spacing would you feel comfortable with? At what spacing would this start to be introduce noticeable differences between channels? In the picture the capsules are spaced ~17cm apart on the vertical axis.
« Last Edit: July 15, 2018, 11:49:35 PM by ycoop »
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Offline heathen

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I think you'd be fine with the spacing you're using.  What the upper limit of vertical spacing is, though, I don't know.
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Offline Gutbucket

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You're good as pictured.  Try to keep the elevation angle identical for both microphones.
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Offline ycoop

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Thanks folks!
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Offline jcable77

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You could have Ted build you some right angle xlr’s to help with your problem of cables being in each others way when there both up on the vertical. Otherwise ones kind of pointing up and the other is pointing down while in DIN. You could try NOS also which is a wider spacing at 90 degrees and that would help.
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Offline relefunt

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It seems to me that you could flip the bracket upside down on the other side (to the left of center in your picture) and have the upright one on the right and then they would be almost right on top of each other. I could be wrong — and if I’m right, then it would be a remarkable “coincidents” I’m sure.

Good luck!
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Offline Gutbucket

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Mostly, you'll want to avoid the "one mic pointing up slightly while the other is pointing down slightly" thing.

You could have Ted build you some right angle xlr’s to help with your problem of cables being in each others way when there both up on the vertical. Otherwise ones kind of pointing up and the other is pointing down while in DIN. You could try NOS also which is a wider spacing at 90 degrees and that would help.

I primarily use right angle female XLRs at the microphone connection, in part for this reason, but also because it makes for a cleaner, more-compact rig aloft.  With the setup shown above, except with both mics either above or below the bar, you can then orient the XLRs so that the cables exit either downwards or inwards.  Similarly, with wider mic spacings one can angle the XLRS so that the cables exit inwards directly toward the stand, pretty much directly in-line with the mic-bar.

And as mentioned in the suggestion to try NOS (12" / 90 degrees), going with a wider spacing that uses less angle between mics also eliminates the mic-body/XLR interference.  That's perhaps a good practical motivation to try the Improved PAS technique which suggests an optimal spacing between microphones based on whatever Point At Stacks angle between the mics you end up with.  For typical PAS angles, you'll end up with the mics spaced wider but angled less further apart, eliminating the mic-body/XLR interference issue while also optimizing for direct sound pickup from the PA as much as possible.

Improved PAS setups - better imaging with higher direct-sound/reverberant ratio-
https://taperssection.com/index.php?topic=167549.msg2087409#msg2087409



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Offline ycoop

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You could have Ted build you some right angle xlr’s to help with your problem of cables being in each others way when there both up on the vertical. Otherwise ones kind of pointing up and the other is pointing down while in DIN. You could try NOS also which is a wider spacing at 90 degrees and that would help.

The picture is deceiving, both are essentially pointed straight forward. Custom cables are definitely in my future though.

It seems to me that you could flip the bracket upside down on the other side (to the left of center in your picture) and have the upright one on the right and then they would be almost right on top of each other. I could be wrong — and if I’m right, then it would be a remarkable “coincidents” I’m sure.

Good luck!

I’m not sure how this would change anything.

And Gutbucket, I have been using PAS for my first few gigs. I want to be able to AB test with a patch I’ll be getting in Tahoe which may be in ORTF.
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Offline relefunt

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Oh, I thought you were trying to run an XY.

I suppose I’ll just read more carefully next time!
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Offline Gutbucket

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As for X/Y-  If anyone cares for a somewhat OT discussion, I can talk about why a taper might want to try an X/Y coincident setup which intentionally introduces an extreme amount of vertical spacing between horizontally-coincident capsules. 

Any guesses as to why one might want to do that?  Hint- It has to do with the oddities of live concert recording in comparison to studio recording microphone techniques where X/Y is typically used.
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Offline heathen

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Is this a trick question where they're oriented 180 degrees from each other, or are we talking more of a "normal" 90 degree XY?
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Offline Gutbucket

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Independent of X/Y angle, using whatever normal X/Y angle is appropriate to the situation.
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made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline heathen

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Increasing vertical spacing = less correlation between the two mics, to give more of a "spaced" feel?
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Offline Gutbucket

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Increasing vertical spacing = less correlation between the two mics, to give more of a "spaced" feel?

Yes, you've got it.

Increased decorrelation of the diffuse sound which essentially arrives at the microphones from all directions.  The idea being that even though the two microphones are spaced apart vertically, they remain coincident in the horizontal plane, such that the direct-sound arriving along the horizontal plane remains tightly correlated (the distance from each source to both microphones is the same), while the majority of the diffuse-arriving sound which arrives from random directions above and below the horizontal plane reaches the microphones with various time-of-arrival differences, decorelating the phase of that ambient pickup like a spaced A-B pair.

That could turn this kind of vertical offset coincident "bug" into a potentially useful feature by pushing it to a greater extreme.

This would probably only apply to concert taping because studio use of coincident stereo mic'ing is typically done at much closer distances, is typically intended for direct-sound pickup with less ambient content, and at closer mic'ing distances it would be difficult to keep the distance from source to each mic close to the same.

An unusual approach no doubt.  But this is the oddball microphone techniques thread!
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Offline DSatz

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In any "coincident" miking arrangement, the transit time of direct sound to the microphones, on average (based on the physical center of where the direct sound is coming from), should be identical. For sounds coming from center, you want to avoid any "precedence effect" (the tendency of the brain to localize according to the first-arriving wavefront--even if the same sound immediately follows in the other channel and is louder), nor do you want any difference in level due to one mike being closer to the sound source than the other. Overall, only the directional pattern of the microphones should enter into the ear/brain's determination of which sounds are arriving from which directions.

The "zenith" orientation of the arrangement as a whole is part of this equation--elevation and tilt are also factors to consider, in other words--particularly if you're doing the crazy thing that this thread is talking about, where a pair of microphones (one directly above the other) is separated vertically. However far apart your "coincident" capsules are, imagine a straight line from the center of one capsule's membrane to the center of the other one. Then choose a point in the direct sound source area that you consider to be its center, and imagine a straight line from there to the midpoint of the line between your capsules. The two lines should always be perpendicular, or else the "coincident" pair should be tilted as a pair to make the lines perpendicular.

As with anything else that's wavelength dependent, higher frequencies are affected more than lower ones by imprecisions in physical setup. But "high-ish" (upper midrange) frequencies are the most important ones for stereo localization, so it's really something to consider.

--best regards
« Last Edit: July 27, 2018, 11:07:26 PM by DSatz »
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Offline ycoop

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Thank you DSatz. I’ve read through this twice now and I will probably need to read it a few more times to fully internalize it.

This raises another question that I was thinking about at the last few shows I was at where I was taping around 10 ft L or R of center. Should I angle my stand so that a line straight from the midpoint of the PA stacks to my rig would be perpendicular with the midpoint of the imaginary line between the “zeniths” of the capsule pickup patterns?

Applying my rudimentary knowledge of SZ theory, I’d imagine this would cause some differences in stretching/squishing of the stereo image on either side of said line from PA stacks midpoint. On the other hand, this might be happening anyway as I am closer to one of the stacks. Currently soundstage seems shifted maybe 10 degrees to the side of center that I was taping from. Could I address this by slightly increasing the levels of the side furthest away or would I be best suited by panning towards the “non-favored” side? Alternatively is this a totally imagined effect resulting from my foreknowledge of my taping location? That last one may be tricky to address. Is there any quantitative way to assess this possibility?

Also my acquisition of a thread extender now allows me to have a separation of only ~2” instead of ~8”
« Last Edit: July 26, 2018, 05:36:22 PM by ycoop »
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Offline heathen

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This thread may have some useful information for you: http://taperssection.com/index.php?topic=185036.0
Mics: Core Sound TetraMic | AT4031s | AT AE5100s | AT853s (C/SC) | Line Audio CM3s | DPA 4061s | CA-14 omnis | Studio Projects CS5
Pre: CA9200
Decks: Zoom F8 | Roland R-05

 

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