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Author Topic: Stronger T-bar extension for spaced omni's - boundary mounted DPA's  (Read 1465 times)

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Offline heesu

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So, my prior setup for outdoor venues has been running a 12" ruler w/ antenna extensions going each way, to get to around ~3'. With just mics like CA14's or DPA's, it was doable, though not the strongest setups.

Now that I have some DPA's, I'd like to be able to run them spaced, with the DPA boundary mounts. First time messing around with this, my current setup was just way too flimsy.

So I guess I'm looking for two things:
1. A t-bar that is either collapsable / extendable out to 3' that will be a bit stronger / not wilt.
2. Ideas for securing the boundary mounts. Gaff tape seems like the easiest, but other ideas area also welcomed.

These are the mounts I'm referencing, by the way: https://www.dpamicrophones.com/accessories/boundary-layer-mount-for-dscreet

thanks!

Offline capnhook

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #1 on: March 27, 2018, 11:16:52 AM »
I made a lightweight spread mount for my tiny CAFS omnis out of a screen-door tensioner...


« Last Edit: March 27, 2018, 02:49:17 PM by capnhook »
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Offline capnhook

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #2 on: March 27, 2018, 11:29:32 AM »
You could attach the boundary mount with a small screw through the holes on the end of the tensioner rod..






Proud member of the reality-based community

BSCS-L->JB-mod [NAK CM-300 (CP-3)][TEAC ME-80 (CP-1)]->LSD2->CA CAFS-Omni->Sony ECM-907**Apogee MiniMe Rev. C->CA Ugly II->**Edirol OCM R-44->Tascam DR-22WL->Sony TCD-D8


"Don't ever take an all or nothing attitude when it comes to making a difference
and being beautiful and making the world a beautiful place through your actions.
Every little bit is registered.  Every little bit.  So be as beautiful as you can as often as you can"

"It'll never be over, 'till we learn."
 
"My dream is to get a bus and get the band and just go coast to coast. Just about everything else except music, is anti-musical.  That's it.  Music's the thing." - Jeb Puryear

Offline aaronji

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #3 on: March 27, 2018, 11:46:03 AM »
Just gaff tape the boundary mounts to the boundary you are using...

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #4 on: March 27, 2018, 12:21:38 PM »
^ No boundary to mount them to.  As I understand it his intent is to suspend the mounts at either end of the bar atop a stand.   The mounts will serve as an Acoustic Pressure Equalizer attachment similar to a sphere attachment but with somewhat different properties.  So not boundary mounted per se, but using the boundary mounts as frequency and polar response modifiers.  I'd like to discuss the particulars of that more here, but first I'll post a bit on T-bars for small spaced omnis..
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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #5 on: March 27, 2018, 12:25:50 PM »
Liking the screen door tensioner rod, Kev.  Nice repurpose.

Heesu, I'll point you to my oddball mic techniques thread in case you aren't aware of it, which began exploring ways of spacing DPA miniature omnis a decade ago- http://taperssection.com/index.php?topic=96009.msg1279052#msg1279052

It's a huge thread, so below are Cliff notes adn selected photos on this particular aspect-

I immediately gravitated to telescopic TV antennas as mic-bar, partly because they allowed me to achieve the width I wanted while being able to retract and fold without disassembly to stow and transport compactly.  The telescoping feature allowed me to adjust the spacing between the mics - both to experiment with the effect of various spacings, and to more flexibly accommodate various recording situations, going less wide than I might wish to when that was appropriate to the situation.  I've never found a superior option and still use variants on the TV antenna telescopic mic bar to this day.

Here's my first setup with a "T"-format telescopic TV antenna simply gaff-taped to a painter's pole-


On the later variants which I still use, the key was making the center connector part out of aluminum bar-stock, to which individual telescopic arms attach and which in turn attaches to the stand.  The upward angled flanges allows for a maximum range of vertical motion of the hinged antenna arms - they fold down and parallel to the stand for transport, up through horizontal to a maximum of about 60 degrees above horizontal-







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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #6 on: March 27, 2018, 12:28:12 PM »
There is a way to gaff tape the cables to the antennas beforehand which allows the antennas to be fully retracted or extended without disassembling everything-







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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #7 on: March 27, 2018, 12:43:32 PM »
This may seem too flimsy, but its capable of supporting a full 6' spread.  To avoid relying solely on hinge tension to keep the arms raised, I bent a portion of clothes hanger wire into a short support bar which attaches to the top of the stand stud and hooks under the antennas to brace them. Its stiff enough for good support but can be bent enough to make the angle whatever I want, and short enough that I just leave it on the stand at all times.  You can see it in this shot looking up from below-



..and in this shot looking down from above-




And that combination is stiff enough to support the antenna arms even when I added full-bodied pencil condensers gaff taped a foot or so out each arm along with the associated XLR cabling - quite a bit of weight on those TV antennas-

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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #8 on: March 27, 2018, 12:51:24 PM »
Anyway, hope that helps or at least sparks you own ideas.

I don't think your bar needs to be especially strong to do what you want to do with it.  For me its all about how to achieve the significant spacing I want (most spaced omni setups aren't wide enough IMO), while being as minimally visually intrusive as possible, providing the flexibility to accommodate various scenarios, and quick hassle-free setup/breakdown.


Happy to discuss what you might expect from your proposed unorthodox use of the boundary mounts if you like.
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made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline heesu

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #9 on: March 27, 2018, 01:20:03 PM »
Thank you Gutbucket! I had you in mind when I posted this, and while I've spent a good bit of time in the oddball thread...I couldn't quite come up with what I was looking for this time.

re: the boundary mounts - yes, I'm interested in using them in the way you mentioned. I don't know that they'll operate exactly as DPA intended them, but interested nonetheless. So to do that, and just for a more robust solution, I wanted to look at some other options for telescoping/extended split omnis.

Thanks capn hook as well - I will look into that option as well.

Offline aaronji

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #10 on: March 27, 2018, 02:37:54 PM »
Happy to discuss what you might expect from your proposed unorthodox use of the boundary mounts if you like.

Interesting; I didn't realize heesu meant boundary mounts with no boundary.  I am curious about the effect in that situation.  I would guess it is considerably less pronounced than an actual boundary or even an APE, particularly given the small size, and thinness, of the mount.  Angle must be an important factor as well, I would think.

Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #11 on: March 27, 2018, 03:31:47 PM »
I don't know that they'll operate exactly as DPA intended them, but interested nonetheless.

Definitely will not be operating as DPA intended.  But that doesn't mean it may not be useful or fun to mess around with.

I would guess it is considerably less pronounced than an actual boundary or even an APE, particularly given the small size, and thinness, of the mount.  Angle must be an important factor as well, I would think.

The frequency response effect of using the DPA rubber boundary mount disks (this way in free space, not attached to a larger boundary) will be more pronounced than an typical APE, or sphere baffle or whatever you want to call it, because the diameter of the boundary mount disk is larger than a typical APE sphere. Both frequency and polar response will be different because the edge of the disk forms a sharp boundary discontinuity.  A sphere is commonly chosen because it is a simple platonic solid with no edge and symmetrical in all axes.  And yes any of these kind of attachments which increase the physical size of the microphone will making it somewhat more directional but only in the upper frequency range where the attachment is "acoustically large" with respect to the wavelength.  So microphone angle will matter and hopefully that trait can be used to advantage.

« Last Edit: March 27, 2018, 04:39:36 PM by Gutbucket »
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made easy- >>Improved PAS table<< | made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline heesu

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #12 on: March 27, 2018, 05:22:53 PM »
Yeah, in a weird was as soon as I got my hands on the boundaries - I wanted to try this. Until I sell my CA14's I can still run them as a backup, but curious to see what kind of effect the boundaries have in this kind of setup.


Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #13 on: March 27, 2018, 07:18:45 PM »
Okay here's the basics on what varius shaped attachments on an omni microphone will do-
They basically work like boundary mounting does, but as a special case in that the boundary is tiny, may not be flat, and the shape of any edge comes into play.  Like "normal" boundary mounting, the size of the boundary determines the range of the effect. The larger the boundary, the lower the frequency range effected. In this case the boundary is very small, and will only affect a range of say 2kHz and higher.

Size of the attachment determines the center frequency of the on-axis response peak and shelf filter boost.  Shape of the attachment determines the how smooth or peaked that on-axis boost is, and the behavior of the response off-axis, due diffraction around the shape and off the edges of the shape back to the microphone element.

A round plate shaped attachment (such as the DPA disk will be when suspended in free-air) will produce a sharper response peak than a spherical attachment, and less-smooth off-axis responses.

A plate-shaped attachment is less common than a sphere, but has been used historically by some manufacturers.  Sennheiser is one I know of, although I can't remember the mic model. TS member and gear builder Jon (Naiant) used to offer an omni which he shipped with a wooden plate attachment (the Naiant X-W).  Below is what he says about it on his website http://naiant.com/x-w-specification/

"The X-W is an electret condenser microphone that uses a 6mm omnidirectional capsule with a 36mm pressure waveplate attached to the capsule mount. The waveplate, fabricated from instrument-grade ebony or bloodwood, provides an increase in on-axis high frequency response which enhances the directional response of the X-W. The X-W’s circuit incorporates equalization to restore the X-W’s on-axis response to nearly flat, with a 2dB presence peak centered at 6kHz.

The X-W thus has improved on-axis signal-to-noise ratio due to the acoustic gain of the waveplate. The 90 degree off-axis response of the X-W is approximately 7dB less than the on-axis response at 20kHz. The X-W exhibits practically no off-axis rolloff below 3kHz."
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Offline Gutbucket

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Re: Stronger T-bar extension for spaced omni's - boundary mounted DPA's
« Reply #14 on: March 27, 2018, 07:19:59 PM »
For a deeper inquiry into the effect of attachments of various shapes-

First a link to an AES paper which is likely to be a definitive source on the subject - Diffraction Effects in High Quality Studio Microphones http://www.aes.org/e-lib/browse.cfm?elib=5902 I've not read it, couldn't find it freely available online, don't have an AES membership and am not paying $20 to download it directly from AES.  But if you have AES library access check that out.

The original research into this was done at Bell Labs back in the late 1930's - The Diffraction Produced by Cylindrical and Cubical Obstacles and by Circular and Square Plates
That study used speakers instead of microphones placed in various shaped enclosures, but the effect of acoustic diffusion around the shape is the same "going out" as it is "coming in".
Below is a figure from that paper which I've pulled from Stan Linkwitz's website (he's referred to it numerous times, I linked the image below from this page- http://www.linkwitzlab.com/Fitz/acoustics-mechanics.htm).  This shows on and off axis response when the source (or microphone) is mounted at the end of a cylinder, a cube, and a sphere.  These are larger baffles about 10" or more in size, but the effect scales linearly with frequency, so just look at the shape of the response curves and ignore the actual frequency indications, or mentally shift the frequency scale upward.  The important thing to note is the difference between the on and off-axis responses, how the response changes further off-axis and how the off-axis response curves are smoothest for a sphere compared to a cube or cylinder-

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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