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Author Topic: Stronger T-bar extension for spaced omni's - boundary mounted DPA's  (Read 1462 times)

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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #15 on: March 27, 2018, 07:38:55 PM »
Before I started making my own spherical baffles, I considered making flat disks, but didn't think of using the DPA boundary mounts.  I was originally thinking of making plate baffles out of the clear plastic "dummy CDR"s which came atop a spindle of blank CDRs, which are somewhat larger in diameter than the DPA boundary mounts. I didn't try that for a few reasons, one of which being it would be a challenge to mount the mics in them such that the solid portion of the mic grid was flush with the front surface of the disk without any gap. That's critical.  A small gap or less than flush mounting will have an audible effect.  You needn't worry about that using the DPA boundary mounts since they are designed specifically for the mics with this in mind (the small opening is engineered to be the correct size to emulate flush mounting).  Actually one thing you might try is attaching the boundary mount disk to a CD or something to hear what effect a slightly larger diameter disk has.  The CD will extend the boundary edge another inch or so radially and lower the frequency where the effects begin somewhat.

I went with spherical attachments for a few reasons- Smoother response as described above, easier for me to make and less of a hassle to setup, less prone to damage and less visually intrusive.  Here's were I started discussing them in the Oddball Mic Techniques thread- http://taperssection.com/index.php?topic=96009.msg1338961#msg1338961
« Last Edit: March 27, 2018, 07:43:10 PM by Gutbucket »
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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #16 on: March 27, 2018, 08:32:11 PM »
Ran across this guy's blog searching today.  Pretty serious research into attachment shapes and measurement of the effects.  I'd like to figure out how to make these kinds of measurements to test some of my ideas and arrangements!

Here's his post on the measurement method and description of what he's doing.  I've not read through it in depth yet, but the part on how to read the plots is informative in understanding the measurements.  He shows polar response plots for an Earthworks omni without any attachment, with flat-faced cylindrical attachement of two different diameters, and a convex-faced cylindedrical attachment.  Ignore the polar phase plots on the right side, its the polar amplitude plots on the left which are of interest with regards to this discussion- https://recordingsofnature.wordpress.com/2011/02/12/visualisation-of-directional-frequency-response/

Here is his follow up post with detailed measurements of various cylindrical pressure attachment geometries on the Earthworks, all of the same diameter, but some with a concave, flat, or convex faces, and with varying degrees of microphone element flushness to that surface (some with the microphone protruding a bit some with it flush, some with it retracted into the hole in the attachemt by a few millimeters.  Quite ingenious use of a roll of 35mm film as variable geometry attachment- https://recordingsofnature.wordpress.com/2011/02/22/pressure-equalizer-geometries-and-directionality/

Also of interest to folks here may be his post with modified Jecklin-disk/dummy-head response measurements comparing various mic spacings from the surface and various surface materials- https://recordingsofnature.wordpress.com/2010/03/21/quasi-binaural-setup/
« Last Edit: March 28, 2018, 09:59:27 AM by Gutbucket »
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Offline Moke

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #17 on: March 28, 2018, 01:47:15 PM »
Well, sometimes you find things when you least expect to.
Objective of the morning: Find/learn about a Pintle tow hitch system.
Found:

https://www.homedepot.com/p/TowSmart-Solo-Hitch-Alignment-System-1280/206798835


Telescoping, extends from 10.5" to 43" each w/ hardish foam ball ends with 2.5" balls. Heavy magnetic bases.
« Last Edit: March 29, 2018, 09:42:58 AM by Moke »
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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #18 on: March 28, 2018, 01:57:38 PM »
Ran across this guy's blog searching today.  Pretty serious research into attachment shapes and measurement of the effects.  I'd like to figure out how to make these kinds of measurements to test some of my ideas and arrangements!

\
Damn those Earthworks sure are sweet mics! Very interesting read on the first two links. As we have discussed it certainly makes for a "better" presentation if one can provide visuals AND even better he provides analysis of how to read/analyze his images.
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #19 on: March 28, 2018, 03:32:47 PM »
Damn those Earthworks sure are sweet mics!

They are.  Very much in the measurement omni camp, small capsule, low diffraction housing and very flat.  A "naked truth" type mic when used for music.

The aspects which make them somewhat less attractive for music tapers are are their power appetite, requiring more phantom current draw than most mics (from what I've heard, haven't used them myself), and that ruler-flat response which is probably going to need some presence-range and up high frequency boost to not sound dull and lifeless at taper distances.


https://www.homedepot.com/p/TowSmart-Solo-Hitch-Alignment-System-1280/206798835

Telescoping, extends from 10.5" to 43" each w/ hardish foam ball ends with ~2"(~+) balls. Heavy magnetic bases.

Nice find.  Can't tell from the photos or descriptions but they look like they may use larger diameter telescoping tubes than TV antennas, which would support more weight without sagging. Too bad they are chrome finished and not black.  The balls can be painted. Wonder if the magnet end screws off.  Lacks a built-in hinge at the fat end for folding that most TV antennas have, but not necessarily a deal-killer.

I should look into carbon fiber tubing again to see if I can put together a telescopic system from that.  When I've searched previously a few years back the only nesting tube options were for larger diameter tubes like for mic booms and things like that, with a minimum diameter of 1" typically and no less than 0.5".  I need something sized more like the tubes used for stunt-kites and drones.
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Offline Moke

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #20 on: March 28, 2018, 07:10:21 PM »
Lee,
This is from the OMT thread, where I posted this same device.

Quote from: Moke
Do I ever leave anything alone?
Only in the bag, on the way home...

Found out:
Magnets just push out of the channels. This exposed mounting scheme of a pop rivet into the body of the tubing.
Determined: Childs play to mod further.
Pop Rivets will be removed, and machine screw replacements. At the magnet channel, matching all-thread connector ferrules will be attached so that the magnetic bases can be utilized, or, the machine screws can be used to connect the two spreaders into a single unit.
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Offline Moke

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #21 on: March 28, 2018, 09:10:01 PM »
OK,... tearing them down, to build them back up.


4793: shows pop rivet
4794: no pop rivet. this is a very deep metal insert flange-lip press fitted into the lowest anchor section. I'm aiming for 1/4-20 male threads for this hole, w/ JB-Weld adhesive set.
4745: I intend to join the new spreader bar like the antique bar, but maybe a bit nicer finish.
4746+: size comps to my antique rabbit ear pair (vintage?)
« Last Edit: March 28, 2018, 09:12:00 PM by Moke »
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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #22 on: March 28, 2018, 09:28:35 PM »
And,.. this just in: the base/anchor section fits the pass-thru hole of the Manfrotto mini clamp really well.
« Last Edit: March 28, 2018, 09:32:56 PM by Moke »
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Offline rocksuitcase

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #23 on: March 28, 2018, 09:55:58 PM »
really nice.  great use of the Trailer Alignment tool. I had to click the link to look at it. Never heard of such a thing! perfect adaptation of their product to the extension bar. kudos
music IS love

When you get confused, listen to the music play!

Mics:         AKG460|CK61|CK1|CK3|CK8|Beyer M 201E
Recorders:Marantz PMD661 OADE Concert mod; Tascam DR680 MKI

Offline Neilyboy

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #24 on: March 29, 2018, 08:00:56 AM »
Love it!  What's under the yellow balls?
Neil
Mic's: AKG C214's, Line Audio CM3, AT4041SP, AT853 (C, SC, O), AT943 (C, H)
Pre's: Sound Devices MixPre 2
Rec's: Sony PCM-M10, Edirol R-44, Tascam DR60D MKii, Tascam DR70D x 2

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #25 on: March 29, 2018, 09:03:01 AM »
From reading a few review comments on the Trailer Alignment tool it seems the balls screws onto a threaded stud at the skinny end.  Should be easily removable.

Way to make quick progress on this, Moke. Looks substantially beefier than the TV antennas yet still not overly large in diameter, so probably capable of supporting larger mics than the miniatures DPAs at a wide spacing, and very compact retracted.  Really nice how it fits perfectly into the Manfrotto mini clamp.

What material are the balls made of?  I can offer some advice if interesting in converting them for use as mic mounts / spherical baffles (APEs).
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made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #26 on: March 29, 2018, 09:17:11 AM »
The foam ball is flexible, but, quite hard. I have to push really hard with a pointed finger in order to distort the shape of the ball. I would call it closer to a reflective surface than an absorbing surface.
It is foam, not hard plastic. But it is quite a hard foam.
The balls are epoxied on, and do not appear to be removable.  I might take a tubing cutter, and cut them away, and, find some precision brass tubing to match the diameter, in order to make a sleeve that can used to remove or replace the balls as needed.

Neilyboy,.
It appears that the chrome extension at the ball is epoxied on. It does not rotate, and there is adhesive residue on the ball at the point, and a spot of it in another location on the ball.

Ball size measured at 2.5" this morning.
matches size of tennis ball, almost exactly.
« Last Edit: March 29, 2018, 09:50:36 AM by Moke »
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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #27 on: March 29, 2018, 11:31:26 AM »
Maybe they changed the assembly since the review I read (where the reviewer discussed unscrewing the balls), or perhaps there's a threaded insert in the ball hidden under the glue.

2" is a bit on the large size compared to most spherical attachments, but that means the effect will start a bit lower in frequency (guessing around 1K or so) and will be a bit more obvious.  Could be advantages, and maybe just the ticket from further back  Definitely worth trying I think if anyone is interested in playing around with spherical baffle attachments.  Most spherical attachments are machined from hard plastic or wood, but I think what's important is that the surface is hard with respect to the frequency range in which the ball is functioning as a baffle, and that it be non-resonant across the full frequency ranges, so I think a firm foam ball with a smooth skin should work fine.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations> virtual teleportation time-machine experience
made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #28 on: March 29, 2018, 11:31:47 AM »
I see two ways of mounting miniature DPAs to these balls.  The first and easiest would be to simply gaff tape the mic to the face of the ball so that the mic grid is held against the surface of the ball and the mic body is tangential to the surface.  I'd point the grid upwards if orienting the ball/mic combination directly forward or angled out +/-45 degrees.  Angled +/-45 degrees is how I run mine and what I'd suggest for folks using them as a spaced omni stereo pair alone at decent spreads.  If using the balls to help make the most of a situation where you are not able to space the mics as far apart as you might like (even though the telescoping bar allows for wider spacings) or if the intent is to use them in combination with a center mic or center pair, I'd suggest taping them to the outermost side of the ball (+/-90 degrees or 180 degrees opposed to each other).  Sort of a double mini-jecklin / dummy-head setup.  That will maximize the level differences.  In that orientation, this taped-on tangential mounting would then allow one to point the mic itself upwards or forwards by rotating the ball.  That probably won't make much difference, but may have some audible effect at the very highest frequencies.

The other more typical way of using the balls, and the method which would need to be used for any mic larger than the miniature DPAs is to make a hole through the ball for flush-mounting. Rather than drilling, which probably won't work well through the foam, I'd suggest either punch-cutting a hole through the ball with an edge-sharpened stiff metal or plastic tube, or melting a hole through it with a torch-heated rod or nail.  A red-hot nail head and a steady hand worked nicely for making holes in my Nerf hard-foam balls.  If the foam ball is compliant enough you might make the hole slightly smaller than the mic body so that it fits snuggly with no gap at the working end.  A section of plastic drinking-straw just larger enough to pass the microphone through, running most of the way through the ball but stopping just short of the surface where the mic peaks out will make it easier to thread the mic through.  If the ball surface gripping the mic body isn't enough to keep the mic in position, a short stick, tapered along its length (I use a piece of chopstick) inserted into the back end of the ball will wedge the mic cable in place without stress or damage.

To achieve variable angles, you can either make multiple balls and switch between them, or poke multiple holes through the ball through which the mic is inserted, or have multiple mounting points for the telescoping arm attachment around the ball.  Mine are setup with a single hole for the microphone and two different blind mounting holes which slip over the antenna button end with a simple interference friction fit.  That gives me options of pointing them directly forward (or behind) or +/- 45 degrees.  I should make another set of holes to orient closer to +/- 90 degrees parlty to accommodate overly narrow spacings, and to see if that offers any further improvement in combination with my center mics even at wide spacings.

The important part is to not have an opening larger than the mic body unless you stuff something in there to fill the gap, and not have the mic stick out or be recessed in the ball.  Ideally only the grid of the microphone should protrude past the surface of the ball, and the the ball's surface should align with the edge of the solid cuff portion of the grid.  It may seem that I'm contradicting myself in suggesting simply taping the mic to the ball, then getting overly particular about the fit in a through-hole, but gaps or small pockets produce more of an audible effect than the mic sticking out slightly.  Consider the difference in response produced by the long high-boost grid verses the short low-boost grid.  Thats a similar acoustic EQ difference produced by a difference of only a couple millimeters of air volume between the mic element and the grid opening.  Recessing the mic in the ball, or a gap around the mic is in some ways similar to changing to a longer grid.
« Last Edit: March 29, 2018, 11:33:41 AM by Gutbucket »
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations> virtual teleportation time-machine experience
made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #29 on: March 29, 2018, 11:46:48 AM »
It strikes me that these tennis-ball sized balls are not much different in diameter in comparison to the DPA boundary mounts.  Would be cool to hear a comparison of the two. 

If the yellow is too garish, a can of automotive spray paint intended for vinyl or fabric seats, tops and interiors remains flexible upon drying and is available in black or various shades of grey.
 
Photo of the chopstick cable wedge-


And a side-view of the wedged-in through-hole mic positioned so only the grid portion is sticking out-


Note- the ball in these photos was installed on the antenna arm with a direct-forward orientation of the microphone.  The ones I actually use are painted charcoal grey.
« Last Edit: March 29, 2018, 11:49:53 AM by Gutbucket »
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations> virtual teleportation time-machine experience
made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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