Jecklin Disk construction?

[John Willett]

Originally Posted by willi1203

Could jecklin disc users tell us what distance is usable ? 16,5cm, 21 cm or 36 cm ?

I use the MBHO disk and the mic. distance is the same spacing as adult human ears.

They say 6", which is about 15cm - so that woukd be 16.5cm on your list.

MBHO Jecklin & Schneider Disks PDF

[heva]

Originally Posted by willi1203

Could jecklin disc users tell us what distance is usable ? 16,5cm, 21 cm or 36 cm ?

Maybe this tool is useful?

[mathieujm]

Originally Posted by heva

Maybe this tool is useful?

I don't see any modelling of the disk arrangement there !

JMM

[Petrus]

Originally Posted by willi1203

Could jecklin disc users tell us what distance is usable ? 16,5cm, 21 cm or 36 cm ?

I use 17 to 20 cm with my smaller 30 cm disk and do not worry too much about the exact distance as long as it is symmetric. The larger disk I have not tested enough (my first organ recordings with it were too thin), I might try it again with acoustic equalizer balls (which I made at cost of 0.75€ each)

[mathieujm]

I just retrieved an old recording from 1994 of a famous quartet.

The recording setup was
- MBHO Jecklin disk
- PRIMO 4550 mics with omni caps
- Uher desk
- Sony DAT

Here is an excerpt from Borodine quartet N°2

JMM

[heva]

Given a speed of sound of 331 meter per second (at 20 degrees Celsius), a Jecklin disk of 35cm would 'work' on frequencies of 945 Hz an higher (331/0.35), lower frequencies would not 'see' the disk (and make it work as a 'regular' 35cm AB). Or would it not?

[mathieujm]

Originally Posted by heva

Given a speed of sound of 331 meter per second (at 20 degrees Celsius), a Jecklin disk of 35cm would 'work' on frequencies of 945 Hz an higher (331/0.35), lower frequencies would not 'see' the disk (and make it work as a 'regular' 35cm AB). Or would it not?

I posted the above example because I like a lot the spacialization and localization of each instrument.
For me, the cello localization on the right is very stable even in the low frequencies. AB don't give similar results.

JMM

[studer58]

I have a question about the 'shadowing efect' of the disk. It's more a function of it's diameter and 'opacity' to the incident sound ? Also the material covering probably plays a part in preventing reflections and phase cancellations (hence the lambswool and other absorptive materials on the faces). I'm thinking of a disk made very light..perhaps reinforced cardboard, with a thin layer of felted material glued on. Would this give the desired shadowing without adding unnecessary mass ? I recall seeing one made of a mouse mat (rectangular) years ago, maybe that was on the right track after all ! See top of page pic at: About Our Microphones

[heva]

Originally Posted by mathieujm

I posted the above example because I like a lot the spacialization and localization of each instrument.
For me, the cello localization on the right is very stable even in the low frequencies. AB don't give similar results.

JMM

Indeed it does, but I wonder if this is because the disk works on the harmonics in the cello's sound (freqs. higher then 1.1kHz), where AB wouldn't?


disclaimer: I'm not a pro rec.eng. so what do I know ....

[Petrus]

Originally Posted by studer58

I have a question about the 'shadowing efect' of the disk. It's more a function of it's diameter and 'opacity' to the incident sound ? Also the material covering probably plays a part in preventing reflections and phase cancellations (hence the lambswool and other absorptive materials on the faces). I'm thinking of a disk made very light..perhaps reinforced cardboard, with a thin layer of felted material glued on. Would this give the desired shadowing without adding unnecessary mass ? I recall seeing one made of a mouse mat (rectangular) years ago, maybe that was on the right track after all ! See top of page pic at: About Our Microphones

Just about anything will give the shadow effect. Some things to consider about the construction:

1) Disk surface should not reflect those frequencies which could cause comb filtering, those are at about 2000 Hz and higher. Almost any felt and fleece on top of few cm of foam should work, I think lambswool is an overkill and looks funny. Ideally the surface should kill all reflections, but that is impossible in practice, use EQ if needed.

2) Disk should be acoustically inert, it must not resonate at all. Layered construction, like plywood with foam, is best. No reason to go overboard with lead/rubber/tar layers like in speaker construction... Lightness is a plus, but not so light that it is structurally to flimsy, mics weigh something, too. Too thin: might flex, not enough sound absorption.

I just recorded the same concert with DPA4060 in AB ("ONNO", no grids) and Senn8020 with 30 cm Jecklin disk with mics about 18 cm apart. AB is clearly brighter, but OSS sounds more solid in soundstage. I would venture to say that the difference in frequency spectrum is partly caused by the HF shadow and possibly some upper low reflection effect from the disk surface. Those can easily adjusted by slight EQ if needed.

30 cm Jecklin somehow feels and sounds RIGHT to me, it seems I am going to use that most everywhere* where the room is good and AB only if the mic is too conspicuous.

*) meaning solo & small groups.

[studer58]

Thanks for addressing these questions of mine Petrus...I use a similarly lightweight mic stand and the 8020 pair also. It seems there's no real need to 'de-couple' (via shock mounting or other suspension) the disc from the stand...it doesn't act as a large sail does on a yacht and transmit significant LF into the stand/mic structure ? I can't imagine a chamber quartet doing this, but a full orchestra with big percussion elements might be on the edge of this (and we aren't entertaining the idea of recording heavy metal or dub reggae bands in small rooms where bass is overblown 300%)...? I think I'll try a 30 cm disc with 18 cm mic spacing and a 35 cm disc with 36 cm spacing (which is the later suggestion of Jecklin) and see what results.
Does the disc allow you to locate your mics further back in the hall than a similar pair of (non-disc) A-B mics ...for the same direct to reverberant ratio ? Or do you place both at the same location for your comparisons ?

[heva]

Made some testsamples with a DIY 35cm Jecklindisk (MDF disk, special soundabsorbing foam) using two matched OktavaMC012's and a FostexFR2LE recording an organpiece (I'm organist) with a 'mixture' stop (high pitched).
Mic spacings were 20 cm and 35cm, settings etc. identical on all takes, but I'm not sure if the mic's were exactly on the diffuse/nearfield border (maybe to near).

Anyway, the difference in in spacing when listening on speaker does not differ very much (maybe due to the fact it's organ), 35cm sounding a bit 'narrower', more 'between' the speakers, where 20cm in comparison goes more to the extreme ends. Also, the 35cm spacing sounds a bit clearer/lighter (especially the 8foot stop in the sound) than at 20cm.

[heva]

Originally Posted by studer58

Thanks for addressing these questions of mine Petrus...I use a similarly lightweight mic stand and the 8020 pair also. It seems there's no real need to 'de-couple' (via shock mounting or other suspension) the disc from the stand...it doesn't act as a large sail does on a yacht and transmit significant LF into the stand/mic structure ? I can't imagine a chamber quartet doing this, but a full orchestra with big percussion elements might be on the edge of this (and we aren't entertaining the idea of recording heavy metal or dub reggae bands in small rooms where bass is overblown 300%)...? I think I'll try a 30 cm disc with 18 cm mic spacing and a 35 cm disc with 36 cm spacing (which is the later suggestion of Jecklin) and see what results.
Does the disc allow you to locate your mics further back in the hall than a similar pair of (non-disc) A-B mics ...for the same direct to reverberant ratio ? Or do you place both at the same location for your comparisons ?

Here is a disk in 'action': YouTube - CATcerto. ENTIRE PERFORMANCE. Mindaugas Piecaitis, Nora The Piano Cat

And how about that pianosoloist ...

[boojum]

As someone who remembers home-brew "hi-fi" gear and speaker enclosures, it seems that the Jecklin is about all we have to tinker with, build and otherwise make a mess in our basements. It has the advantage of being a true recording tool whose fabrication is simple and cheap. Anyone with an old LP and some sound absorbent foam can make one. And you can get good results. And like the other home-brew gear, it stimulates hours of discussions. All hail Jecklin.

I may get mine out and start some tests with it.

[Corran]

Originally Posted by heva

Here is a disk in 'action': YouTube - CATcerto. ENTIRE PERFORMANCE. Mindaugas Piecaitis, Nora The Piano Cat

And how about that pianosoloist ...

This clip is actually what got me interested in the Jecklin Disc. I love the recording. The piece, well the "concept" is a little silly I think but the music is nice.

BTW, I just got a cool deal on a used J-Disk (how's that for rare?), the one from Core Sound. If anyone wants detailed pictures, I can provide, for study purposes.

[klankschap]

Originally Posted by Walling1

Does anyone actually sell them? I can't find anyone who makes them.

You could check the lazy disk at
Floris van Manen
easy to build, carry and use.

http://www.klankschap.nl/ndotb.pdf
http://www.klankschap.nl/LazyRig.pdf


.F

[heva]

Recorded THIS in a concert with my DIY Jecklin disk, 36cm, oktava012omnis@35cm, 2m behind conductor +/- 4m high pointing to the middle of the stage (which was 8m wide and +/- 6m deep). Little bit of EQ lift between 2k and 10k.

Interested to here reactions.

[klankschap]

Originally Posted by heva

Recorded THIS in a concert with my DIY Jecklin disk, 36cm, oktava012omnis@35cm, 2m behind conductor +/- 4m high pointing to the middle of the stage (which was 8m wide and +/- 6m deep). Little bit of EQ lift between 2k and 10k.

It seems a rather large space for a chamber choir
Instead of lifting between 2 and 10k, you can also reduce 1.5 dB around 700Hz
I use a somewhat large base (40 .. 45cm) but it is not too critical.
Depends on the quality of the microphones...

[dgpretzel]

An old thread, but why start another new one on J-Disc construction techniques?

I'm wondering about the function of the disc, itself. When folks speak of using an old LP, or thin plywood, it makes me wonder if the main purpose of the disc is actually structural. By that, I mean something to which to attach the foam. Anything that thin wouldn't have much sound aborption or reflective function, would it? Even if the material characteristics were such that it did, it would only affect very high frequencies, due to the (lack of) thickness, no?

So, if it mainly serves as a way to support the foam, what if one has foam that needs no such support. I am thinking of Johns Manville Linacoustic RC duct liner, which actually has pretty good absorption characteristics (and, in addition to being used as duct liner [for sound deadening], has also been used effectively in the wall construction of home theaters, specifically because of its good absorption characteristics).

Linacoustic has a coating on one side of it that makes it semi-rigid. It is similar to common fiberglass insulatiion, but a bit denser. It comes in various thicknesses, but I have some in 1" thickness. I cut two circular disks, and can place them back-to-back in a 14" embroidery hoop, and the whole thing is extremely light weight, and stands alone quite well.

I plan to use a stereo bar to mount some SDC mics, and the j-disc will just be a (fleece-covered duct-liner insulation) baffle between them, with nothing (no microphones) actually attached to it. Thus, it wouldn't need to support anything, and it's "light as a cloud".

Is there something to be gained by adding a thin piece of plywood or plexiglass?

Curious,

DG

[John Willett]

Originally Posted by dgpretzel

An old thread, but why start another new one on J-Disc construction techniques?

I'm wondering about the function of the disc, itself. When folks speak of using an old LP, or thin plywood, it makes me wonder if the main purpose of the disc is actually structural. By that, I mean something to which to attach the foam. Anything that thin wouldn't have much sound aborption or reflective function, would it? Even if the material characteristics were such that it did, it would only affect very high frequencies, due to the (lack of) thickness, no?

So, if it mainly serves as a way to support the foam, what if one has foam that needs no such support. I am thinking of Johns Manville Linacoustic RC duct liner, which actually has pretty good absorption characteristics (and, in addition to being used as duct liner [for sound deadening], has also been used effectively in the wall construction of home theaters, specifically because of its good absorption characteristics).

Linacoustic has a coating on one side of it that makes it semi-rigid. It is similar to common fiberglass insulatiion, but a bit denser. It comes in various thicknesses, but I have some in 1" thickness. I cut two circular disks, and can place them back-to-back in a 14" embroidery hoop, and the whole thing is extremely light weight, and stands alone quite well.

I plan to use a stereo bar to mount some SDC mics, and the j-disc will just be a (fleece-covered duct-liner insulation) baffle between them, with nothing (no microphones) actually attached to it. Thus, it wouldn't need to support anything, and it's "light as a cloud".

Is there something to be gained by adding a thin piece of plywood or plexiglass?

Curious,

DG

The BBC actually used to use a Jecklin disk made of perspex with no foam at all.

The main thing is the size of the disk with the approximate blocking characteristics of the human head.

The foam is to minimise HF reflections.

[David Spearritt]

Originally Posted by John Willett

The main thing is the size of the disk with the approximate blocking characteristics of the human head.

For loudspeaker or binaural playback?

[John Willett]

Originally Posted by David Spearritt

For loudspeaker or binaural playback?

Yes

[Sheikyearbouti]

I have now 3 DIY disks and I am keen to try Schneider disk and as well compare my designs with some of the commercial.

Here is link to pictures of the second disk I made. http://georgievsound.com/uploads/201...uction-www.jpg

The first one was made of some sort of plastic with a bit of acoustic foam on top and didn't work well. I use it now mostly as a Snare/HH isolation baffle - I put it in between and get rid of the high frequency spill of the HH in the snare spot mic.

The second one I designed is very solid - plywood, cork & acoustic foam. The disk has been very useful. For example in decent but not amazing halls it clears the image - essentially what you are doing is to reduce the reflections from the sidewalls in the opposite side mic. So left mic gets less from the right wall and vise versa.

This gives me the possibility to put the mic further back in the hall - you reduce the amount of reverb by using the disk!

The other great thing is that more 3D picture, more defined low end too! Such with omnis IMHO otherwise is impossible (unless some sort of other additional directionality technique is employed). Well, this is what the disk does for me - you get a good dose of intensity difference, and not just any kind - a frequency dependent one. So all great!

But I had a problem with the disk clearly altering the sound of the recorded instrument. It has worked great on small ensembles, quartets, etc. But I tried it on a solo classical guitar and the timbre of the instrument was definitely less natural. On classical guitar duo it worked very well!

So I did a few tests - nothing scientific but below you'll see a few measurements. I am curious if someone else has experienced those problems.

Basically I put the disk on a stand in front of one of my speakers and sent some white noise and recorded it. The mics in all cases were at 90º to the speaker. So it is not about my speakers, the mics (KSM141 in omni) or the exact placement. The point is what happens when I remove the baffle - what is the relative difference - quite interesting IMO.

I wonder if the commercial disks fail in this way. I am currently building a third disk and will try to improve this. Let's see how it goes.

One thing which might be a flaw in my tests is that the mic was quite close to the speaker - in real life the instruments are not that close - any comment is welcome!

--------------

This is a measurement taken from a KSM141 in omni on the stereo bar (same construction on which the disk goes), speaker blasting at 90º of the capsule white noise.



--------------

Same as above but with the disk on - so this is not behind the disk! The mic gets the sound directly from the speaker but the disk is behind the mic. I made a big effort to NOT move the stand, and I am sure the position of the mic is exactly the same.

What is interesting he is the this is not a comb - it is some sort of other anomaly.



--------------

This is a measurement of the other mic which is behind the baffle - so this is essentially the shadowing effect of my baffle.

[2manyrocks]

What is the slotted, L shaped piece of metal with 5 holes in the photos in your link? Obviously, it's something to connect the disk to the mic bar, but what is it?

[Sheikyearbouti]

Oh, I made that with the help of a friend. I have 3 of them now, 1 for each disk. It is just what you use to screw the disk & stereo bar on, and than what connects them to the stand. Nothing you can buy, but if you have the right person it is an easy DIY.

Here is a little article I wrote about the disk. Haven't had the time to update with samples yet.

[David Spearritt]

Originally Posted by John Willett

Yes

You can't have both John. It's one or the other.