Jecklin-disc DIY from vinyl ?!?

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clintrubber

Well-known member
Joined
Jun 3, 2004
Messages
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Location
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Anybody using a Jecklin-disc for stereo recording ?
(OSS: optimum stereo signal)

A ready-made one is silly priced, so the DIY-examples on the web are countless.

What surprises me bigtime though is that at the prescribed 12" diameter
most people use wood for the centre disc but nobody seems to simply glue
a few 12" vinyl records together.

Not a good idea ? Anybody been there ?

I figure that a few Barry White records can give a firm enough center-disc,
add some foam and ready.

No idea yet what kind of glue would be best, but I have enough old fleamarket records to try.

Curious to hear about your experiences of using a Jecklin-disc as well.

Bye,

Peter

jdisk.jpg
 
My experience with Jecklin disks have been disapointing; very coloured sound. Don't know of any pro still using this stuff for classical recordings. Stronlgy recommend spaced omnis instead.

Samuel
 
[quote author="Samuel Groner"]My experience with Jecklin disks have been disapointing; very coloured sound. Don't know of any pro still using this stuff for classical recordings. Stronlgy recommend spaced omnis instead.

Samuel[/quote]
Hi Samuel,

Thanks for responding. Surprised to hear about the colouration actually, but your words from actual use and the favourable comments from 'PR-texts' (not: PRR ;-)
Sounds like it has been a method that's abandoned again ?

My usage would be band/rehearsal-recording (say ~~rock) in a stage-like setup.
While I get nice results from either card-condensers in NOS, or indeed a pair of spaced omni's (dynamics: a pair of Beyer M101NC), I'm always curious to what other setups can bring, hence my interest in the Jecklin-disc.

Who knows, maybe it's even more unsuited for my application than it already might be for classical ?
It won't set me back much to make, so will try it anyhow, but thanks again for sharing the experience.

Regards,

Peter
 
I've recorded some club gigs with a jecklin disk setup and it seemed to work pretty good for that, but you want it much closer than I was able to place it.
In the back of the club it sounded just like you were standing there, including the guys talking about more beer ...

I made mine from 1/4" plexiglass because it was on hand and fit an old broken mic clip.

jecklin1.jpg


I used a router to make the circle cut out by tracing a wooden cable reel with a flush cut bit.
 
[quote author="BradAvenson"]I've recorded some club gigs with a jecklin disk setup and it seemed to work pretty good for that, but you want it much closer than I was able to place it.
In the back of the club it sounded just like you were standing there, including the guys talking about more beer ...[/quote]

Thanks Brad for posting. That purple looks stylish !

For our rehearsal stuff the required closer placement won't be a problem, since it's just us on the stage, nobody in front of it (some gigs may be alike :twisted: :wink: ), so the setup can be right in front of it.

That's at least where I put the spaced omni's now; I'll check the table on this page for a starting guideline where to put the Jecklin-arrangement.

Did you experience advantages over the 'usual' setups ?

Regards,

Peter
 
I bet a layer of 1" or 2" rockwool on each side of the disc will give better (more even) frequency absorption than foam.
 
[quote author="wmtunate"]I bet a layer of 1" or 2" rockwool on each side of the disc will give better (more even) frequency absorption than foam.[/quote]
I'm not too familiar with rockwool, but are there versions that don't give potential hassle with small fibres etc ? Such a disc gets handled, thrown around etc.

Bye,

Peter
 
> a few Barry White records

That will give your recordings a colored sound!

Capsules a few inches out from the center of a 12" circle will show STRONG midband resonances. You really want some kind of fuzz on it. With enough fuzz, the disk material is moot. Carpet, foam, old plaid shirt cloth, old glam-rock wigs, whatever. And off-center on a non-circular shape seems wise.

> the table on this page for a starting guideline

What, the diffuse distance? IMHO, if you can't already estimate that within seconds of walking into a room, you should just mike everything and re-arrange it on the 24-track desk.

Hint: concert hall 11 feet, living room 4 feet. Low-ceiling beer-dives are treacherous. When empty the critical distance may be a few feet, when full there may be no reverberant field (Dc is beyond the far wall).

Get a pocket radio and a $29 SPL meter. Crank the radio on bad AM pop music (nice consistent level) and walk away. At first the SPL drops 6dB for each double distance. At the far end of the room, level is constant everywhere. Walk from the far end until SPL rises 3(?)dB, that is Dc. Work between Dc and 3*Dc for clarity. If the room don't suck, many types of music can stand going much further than 3*Dc. (Some types music sound best outside the building.........g)
 
[quote author="PRR"]> a few Barry White records

That will give your recordings a colored sound!

Capsules a few inches out from the center of a 12" circle will show STRONG midband resonances. You really want some kind of fuzz on it. With enough fuzz, the disk material is moot. Carpet, foam, old plaid shirt cloth, old glam-rock wigs, whatever. And off-center on a non-circular shape seems wise.[/quote]
Sounds as that off-center is the best way to do it indeed, yet that's the way that it seems to pop up most frequently, the first pic above from a respected manuf. included :roll:

But given enough damping the resonances will become less or vanish again one could say, but there is also the so-called Schneider-disc out there which does an additional something:
The Schneider disc is a
variation of the Jecklin disc
developed by Jürgen Jecklin
for his stereo microphone technique known as Optimal
Stereo Signal (OSS). The idea behind OSS is to
use a pair of spaced omnidirectional microphones
approximately 6 inches apart (roughly the distance between
the human ears) with a disc placed in between the
spaced pair. The disc is covered with a thin layer of
foam intended to absorb high frequencies - thus improving
stereo separation between the microphones. The
difference between the two types of discs is the foam
sphere at the center of the Schneider disc, which reduces
the amount of high-frequency energy reflected from
the disc, and results in an increase of stereo separation.

Below approximately 200 Hz, the Schneider disc has
little (if any) effect on the stereo signal because the
audio wavelength is large enough to bend around the
disc, equally reaching both microphones. However as
frequency increases above 200 Hz, the Schneider disc's
foam sphere increases stereo separation between the
spaced pair.

> the table on this page for a starting guideline

What, the diffuse distance? IMHO, if you can't already estimate that within seconds of walking into a room, you should just mike everything and re-arrange it on the 24-track desk.
I see what you mean, just was having a let's these folks see some use of that table mood... while I know that in practice it'll just be slammed onto a stand in a hurry since we need to get started, despite the neat thoughts before.

Get a pocket radio and a $29 SPL meter. Crank the radio on bad AM pop music (nice consistent level) and walk away. At first the SPL drops 6dB for each double distance. At the far end of the room, level is constant everywhere. Walk from the far end until SPL rises 3(?)dB, that is Dc. Work between Dc and 3*Dc for clarity. If the room don't suck, many types of music can stand going much further than 3*Dc.
Nice idea to do such a measurement, it should serve as the last argument that was missing to make me undust'n'finalize my DIY-version with the way too expensive AD636JH I once bought :thumb:

(Some types music sound best outside the building.........g)
Round circle, we're back to Barry again :wink:
But that's kidding, I sure like his music now & then.

Regards,

Peter
 
[quote author="clintrubber"]What surprises me bigtime though is that at the prescribed 12" diameter most people use wood for the centre disc but nobody seems to simply glue a few 12" vinyl records together.[/quote]

I have. I've built a cross between a Jecklin disc and a boundary layer microphone by mounting half an LP (that's a vinyl record for you furriners) perpendicular to a ~12x12in piece of thin fibreboard ('hardboard'). Used two Linkwitz-modded WM-61A omni electret capsules directly on the hardboard plate equidistant from the center of the LP, with a simple fixed 20dB OPA2134 mic pre powered from a 9V battery. The LP is covered with teddy bear fur (leftover from a DIY stuffed animal), bought for ~5EUR at a local fabric shop.

There is a name for this contraption (Jecklin/boundary mic hybrid), but I can't seem to remember ATM.

It works well enough; the fibreboard base is thin enough so that when you place it on the floor/stage you do get the boundary layer effect. Stereo imaging is quite good, and it's hard to beat at the price.

If you're planning to mix a record, this might not be the best mic choice ever. If you're just taping stuff for your fan site/to have a demo for interested venue owners/to analyze your band's performance afterwards, you could do a lot worse than this contraption hooked to a MD recorder or similar.

If you want I can dig up some sound samples, or get the beast out of storage and take a few pictures. Heck, if you feel like experimenting I can probably send you a couple of WM-61s. They're pretty good for what they are, and as you know a Jecklin disc requires 'true' pressure transducers, not multi-pattern mics set to omni.

JDB.
 
[quote author="olafmatt"]From what I've read Jecklin made his first discs from 12" vinyls.[/quote]
Great minds think alike ! :cool: ehh sorry

As PRR pointed out, you need some sort of absorber on that. Jecklin used felt.
I made mine from 10mm wood (MDF, because it's easy to work with) with 20mm acoustic foam on both sides.
Sure, I didn't expect to get away with just that pile of LPs, but it's easier to grab some vinyl than to cause sawdust.

In Jecklin's recent papers he talks about new dimensions. The 'old' disk has a diameter of 30cm (12") and mic distance of 17cm (capsule-to-capsule). New dimensions are 35cm diameter and 36cm (!) capsule distance.
Uhh, 36 cm, well OK, let's not make jokes about increased headsize....

by one of it's biggest enemies: http://www.sengpielaudio.com/EineScheibeOhneOhrabstand.pdf
Uhh, what's going on, competition ? I'm aware of the Sengpiel-site, didn't knew about the animosity...

Regards,

Peter
 
Hi JD,

[quote author="jdbakker"]I have. I've built a cross between a Jecklin disc and a boundary layer microphone by mounting half an LP (that's a vinyl record for you furriners) perpendicular to a ~12x12in piece of thin fibreboard ('hardboard').[/quote]

Interesting combination of Jecklin & boundary :thumb:
And that teddy bear stuff is nice as well, part of the fun of using such a contraption is in the neat finishing (I've seen some messy foam jobs on the web)

If you want I can dig up some sound samples, or get the beast out of storage and take a few pictures.
If not too much work, sure, yes please, that'd be nice.

Heck, if you feel like experimenting I can probably send you a couple of WM-61s. They're pretty good for what they are,
I'll email you about that tonight, thanks.

and as you know a Jecklin disc requires 'true' pressure transducers, not multi-pattern mics set to omni.
Yes, check :thumb: I have no pair of true omni-condensers (yet), but had the pair Beyer dynamic omni's in mind I recently bought. Previous plan was to employ my MD-21-ish mics, but the Beyers will be better alike.

Bye,

Peter
 
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