Topic: Oddball microphone technique (OMT) - part 4

[Gutbucket]

^ Hack it and do your own laser light shows!

Had to go look for a photo of Michael William's old school analog angle finder. The "Crocodile". Like hauling a piece of hardwood furniture around!

[checht]

New OMT4 rig

Last night was 6th of 8 Los Lobos shows in Hawai‘i and Seattle. I ran OMT4 with mk41s x/y PAS in the center and mk22s 4’ split, plus a stereo SBD feed.

I’ve assembled a new OMT4 rig, as V1 took me too long to setup/take down and is relatively heavy. It was built of 15mm al rods, 4 shock mounts, and lots of other hardware. V2 is built around a SRS 3D-printed nylon mount that does x/y and flies 2 - 2’ carbon fiber rods as split omni booms. Whole thing weighs 269g so can be mounted on one Rycote INV7-HG MKIII. The x/y portion can accommodate Movo windscreens when needed. It fits in my bag with the mk41s in place, so I just pop it on a stand, clamp on the 2’ rods, and put the mk22s on. So much easier/faster, and it's more than a pound lighter than V1. I've got the 22s on shock mounts for extra isolation, but may direct mount them to the booms.

Final addition to the rig will be wedges that angle the rods back at 18.25º so that the caps end up 7.5” behind the center pair. Scott’s working on them now.

Pictures of V2 below.

If folks are interested, I can post samples.

[Gutbucket]

Nice!  Way more streamlined and compact.  I totally relate to efforts to make setup and breakdown quick, repeatable, futz and error free, especially when they also make the flown array lighter and significantly less visually imposing.  IME, these kind of improvements are what make using these arrangements practical to use on a regular basis, and not overly imposing and/or a PITA to run.

How wiggly is it with the outrigger arms in place and the entire thing supported by that single vertical duel-lyre suspension in the center?  Using different suspension elements less capable than the Rycote Lyres to do something similar in suspending everything above the stand-connection point as one single unit, I found that achieving just the right springiness was a challenge. Needs to be floppy enough to effectively isolate the array from solid-born vibration transmitted through the support stand, yet at the same time, firm enough to not tilt or droop too easily. In playing around with that last year I was not able to get that to work satisfactorily, so have gone back to rigid mounting for now. A dual lyre using the appropriate durometer lyres is likely to work much better as it distributes the twisting moment over a significantly larger leverage area. Even if suspension hasn't really seemed necessary for my setup, I'm still scheming about ways of incorporating a less wiggly shock mount system that provides effective vibration isolation the next time I do a major rework of the setup.

If that Rycote shock mount in the center suspending the entire array is doing a sufficient job of isolating the X/Y supercard pair from vibration through the stand, it should also be sufficiently isolating the spaced pair.  Plus, the use of more open patterns in the spaced pair position will naturally make them less susceptible to solid-borne noise transmission than the supercards in the center.  I'd definitely try it with the spaced pair mounted directly to the rods as that will make it significantly more streamlined.  Little adjustable-angle mic clips extending out from the ends of the tubes would be great, making it exceptionally visually clean by placing the mics in-line with the rods, and that would also maximize the spacing you can achieve.  Extra credit if you are able run a small diameter mic cable through each tube!

I've been thinking about reworking my rig with carbon fiber tubes in place of the TV antennas for long time, but don't want to give up the super small diameter and telescoping extension feature.  All the bits for making telescoping c/f rods I've seen use tubes of an overly large diameter, typically boom poles, and use large locking telescopic fittings which aren't necessary for this application.  Just need them to telescope in/out with a hard-stop and a friction fit that makes them sufficiently rotationally stiff.  Stunt-kite style c/f tubes are about the right diameter but telescoping end bits for them don't seem to be available.  With the TV antennas, the ends of the thin steel tubes are simply swadged down at one end and flared at the other, and they have sufficient friction to avoid rotating.  Would be really great to incorporate a very small diameter mic wire through the telescoping c/f tubes, but that wire would need to be spring-coiled to accommodate the telescoping. Fortunately all the mics I'm using on arms are currently two-wire.

How well do those little clamps secure the two highly cantilevered rods?  Any sign of sagging or is the center mount stiff enough to avoid that, as well as being strong enough to avoid cracking at the base of the clamps?  If that seems like it might be a potential problem, you might make a piece that inserts an inch or two into both two tubes, connecting them together to eliminate the bending stress.

[audBall]

Whole thing weighs 269g

Very cool. Thanks for sharing.

[checht]

How wiggly is it with the outrigger arms in place and the entire thing supported by that single vertical duel-lyre suspension in the center?  Using different suspension elements less capable than the Rycote Lyres to do something similar in suspending everything above the stand-connection point as one single unit, I found that achieving just the right springiness was a challenge. Needs to be floppy enough to effectively isolate the array from solid-born vibration transmitted through the support stand, yet at the same time, firm enough to not tilt or droop too easily. In playing around with that last year I was not able to get that to work satisfactorily, so have gone back to rigid mounting for now.

I'd definitely try it with the spaced pair mounted directly to the rods as that will make it significantly more streamlined.  Little adjustable-angle mic clips extending out from the ends of the tubes would be great, making it exceptionally visually clean by placing the mics in-line with the rods, and that would also maximize the spacing you can achieve.  Extra credit if you are able run a small diameter mic cable through each tube!

Getting the suspension right has been tough. I tried w Rycote single lyre mounts, Schoeps regular and heavy elastics, and the AKG shock mount, but none were right. It was a Goldilocks situation. I took a chance and ordered the dual lyre, and lucked out. It's a bit more see-saw than I'd like, but reducing the weight/leverage at the end of the booms has helped a lot. I've got some active cable clips from SRS and will bolt them directly onto the rod clamps, for a lighter and lower profile mount.

I've been thinking about reworking my rig with carbon fiber tubes in place of the TV antennas for long time, but don't want to give up the super small diameter and telescoping extension feature.  All the bits for making telescoping c/f rods I've seen use tubes of an overly large diameter, typically boom poles, and use large locking telescopic fittings which aren't necessary for this application.  Just need them to telescope in/out with a hard-stop and a friction fit that makes them sufficiently rotationally stiff.  Stunt-kite style c/f tubes are about the right diameter but telescoping end bits for them don't seem to be available. Would be really great to incorporate a very small diameter mic wire through the telescoping c/f tubes, but that wire would need to be spring-coiled to accommodate the telescoping. Fortunately all the mics I'm using on arms are currently two-wire.

C/F has great benefits, but is harder to machine and make homebrew solutions for. Great idea on running the wire through the tube, I think my tubes are large enough to accommodate the binder plugs on my active cables, will try tonight.

How well do those little clamps secure the two highly cantilevered rods?  Any sign of sagging or is the center mount stiff enough to avoid that, as well as being strong enough to avoid cracking at the base of the clamps?  If that seems like it might be a potential problem, you might make a piece that inserts an inch or two into both two tubes, connecting them together to eliminate the bending stress.

The rod clamps are made to use with 15mm al rods for video camera setup, and are very robust. I tested them by putting a lot of force on the ends of the tubes, with no deflection noticable. When I add my angle wedges, the tubes won't be parallel any more, so I'd need to make a 3D printed piece to insert.

[al w.]

Nice setup!

[Gutbucket]

Thanks.  That further confirms my suspicion that the best solution for suspending the entire array as a single unit while avoiding excessive see-sawing is sufficient spacing between the suspension points, which the dual lyre arrangement helps to achieve.  The suspension points can be spaced vertically or horizontally, either way it spreads out the rotational see-saw moment across a larger lever arm.  The dual lyres can be used in either orientation, but are most compliant in the axial direction.

In my next build I'm thinking of trying a few spaced-apart low durometer Sorbathane pucks around the periphery of a horizontal plate that forms the center hub.  Will take some prototype testing with headphones on.


It kind of looks like that center X/Y mount allows for adjustment of X/Y angle.  Is that the case?

[checht]

Yes, the main part has slots in which curved pieces fit and rotate to set x/y.
There is also a 3rd slot down below for more vertical spacing of caps when using large windscreens.
See renders, attached.

[Gutbucket]

That's well thought out and very cool!

[checht]

Mr. Bucket,

Your comments got me thinking, and I've updated with a very low-profile and light mount for the omni caps.
It uses the neoprene expansion nuts that I didn't use for mounting the booms due to their deflection. In this application, the weight and leverage are so minimal that deflection isn't an issue.
See photos below.

Still have to design and print wedges to angle the booms back to get them behind the x/y pair, but almost complete!

[phil_er_up]

Nice set up Chris. Gets me thinking about if I should change up my rig...

[rocksuitcase]

checht
That is some good looking modifications. kindms owns a camera rail set up with 15mm carbon fiber rods we occasionally use for split dpa omnis. he purchased the stock rotating mounts for them and attach the nbob active clips like yours to that. Your idea is very ingenious.
Thanks for showing us.

[Gutbucket]

Chris, you've inspired me to think more fully through the next revision of my OMT8 rig, which I've been planning on reworking for a while.  See the attached PDF if interested.

The primary change will be the central support hub. The arms and overall geometry remain the same as before and I plan to stick with the black telescopic TV antennas for at least the outer portion of the L/R arms out to the omnis, but might switch to carbon fiber kite tubes for inner portion of those, or not.  Also may use carbon tubes for the rear facing pair arms, since I don't actually telescope those in use.  My most recent previous revision switched out the center forward-reaching telescopic TV antenna arm for a standard folding mic-clip, since like the rear-facing pair I no longer actually telescope it in use, and I plan to retain that standard folding clip so I can easily switch between the stereo shotgun I'm currently using in that position, the DPA/Naiant Mid/Side pair it replaced, or any other M/S pair I want to try.

The new single-piece central support structure will replace a stack of several aluminum arm supports I've used and reworked for over 15 years, supporting all five arm attachment points with the correct a pentagonal geometry, eliminating the need for little angle tweaks between arm pairs to get everything lined up right when deploying it on the stand, foot, or clamp or whatever.  That should both simplify and streamline the arrangement, cleaning it up nicely.   

The key component here is the pentagonal top plate (in orange in the PDF) to which all the arms attach. I'll probably build just that part first with a spigot stud on the bottom which mates to my various support options, the same as my current rig works.

But I've gone ahead and drawn it up with vibration isolation incorporated into it to reduce solid-borne noise transmission though the stand and cable. As mentioned, incorporation of suspension is really just something of a nice to have addition for me, but.. it will be nice to have, and this is an opportune time to consider it in the redesign.  To do that the spigot stud gets moved from the top plate to a lower plate, which supports the top plate though 5 Sorbathane damping 'pucks' of sufficiently low durometer to be effective, positioned around the periphery of the top plate between arm attachment points so as to form a sufficiently wide support basis that hopefully keeps the top plate part and arms stable and not too wiggly.  Bottom plate would be a spider or asterisk shape to allow the arms to fold down bewteen its notches for stowage / transport.

Also considering incorporating a multi-pin connector into the bottom plate, to which the cable bundle could be disconnected.  Alternately, that will be a good place to incorporate Cat 5 /6 baluns which would eliminate the current cable bundle and further streamline things, but I'd still need two Cat 5 /6 cables to support all 8 channels.

I plan to fabricate this from aluminum plate, but also thinking it could be nicely 3d printed, using sufficiently tough materials such as whatever Scott at SRS uses.

PDF of the current concept is attached.  The key illustrations are all on page 1. Page 2 is just an aesthetics comparison of a few different top plate shapes.  I'm leaning toward the slightly starfish shaped version over the inflated pentagon.

[checht]

Very interesting and inspiring! A number of innovations in the new design which I'll be very interested to observe, the al plate and isolation system primary among them. Going to ethercon snakes makes sense, and I'd also take a look at what Redco has in 8 channel just to consider the convenience of 1 cable/connector.

Please keep us updated as you go along, pictures much appreciated.

[Gutbucket]

Will do, and thanks for the tip on checking out the Redco options.

Thinking further on wiring.. If the unicorn of a two-wire miniature fig-8 actually existed I could potentially fit everything through a single 9-conductor connection, in which case a single ethercon run using shielded Cat 5 / 6 (shield acting as shared ground) might work.  Would super slick to be able to use a single Cat 5 / 6 run between the mic-array and the recording bag!  Not sure about that though as it would require spiting up the individual wires of each twisted pair between two different microphone channels and I'm unsure if cross-talk might be too much.  In a typical ethercon run supporting 4 balanced connections the twisted pairs are a benefit rather than a potential problem because each mic channel is assigned its own twisted pair, and any cross-talk between the two wires of the pair will be common-mode rejected by the balancing.

But to support any real-world-available fig-8 (balanced 3-pin XLR) requires one additional wire making for 10 conductor paths total, and supporting the stereo shotgun I'm currently using requires two additional wires (5-pin XLR at the mic, both Mid and Side balanced), requiring 11 conductors total with a shared ground.

If I didn't go ethercon, a single 9-pin D-Sub connector using the D-shell as the 10th contact for the shared ground would suffice in support of an unbalanced Mid through my current multi-conductor snake.  In that case an off-the-shelf VGA monitor extension cable might work for the run from the mic array to the PFA/XLR-adapters at the recorder. And before incorporating the stereo shotgun into the array that uses a balanced Mid, that was my plan.  But I probably won't go that route now because I want to support the balanced shotgun and accommodate alternate balanced center stereo-pair options.

Two ethercon connections could of course do it of course, as that could fully support 8 balanced mics.