Jecklin disk, 17 or 35 cm mic distance?

[Petrus]

I have been using a modified Jecklin Disk first with Oktavas and now with Sennheiser 8020. It is 30 cm in diameter and has one to two layers of foam (thicker in the middle) + grey fleece cover. Mic separation has been about 17 to 20 cm.

Now Mr Jecklin has updated his disk to 35 cm diameter with 35 cm mic separation. Has any of you compared these two? What is the main difference?

I have used my disk for chamber orchestra and for organ. I would imagine that smaller scale sets like string quartets might not gain much if any from greater separation, but organ maybe, even using just AB with 60-90 cm separation with them.

So, is it worth making a 5 cm extesion ring and mic spacers for my rig?
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My first post here. I use SD722 for recording, ATH-M50 headphones, ADAM A7 nearfields, ADAM S3A + Genelec 7071A for main monitoring. Adobe Audition 1.5 + CD Architect 5.2 for post & authoring.

[boojum]

I never tried the narrower spacing. Jecklin already did the comparisons. He likes the wider spacing. ;o)

I am rigging a setup with the 12" disc, covered with foam and then that covered with faux lambs wool and adding a set of DPA 4006 TL's. Jecklin used these in his design so I am hopeful of stellar results.

Again, I would go with the 35cm. It has been tested; I trust Schweiz Rundfunk.

[mathieujm]

Originally Posted by Petrus

Now Mr Jecklin has updated his disk to 35 cm diameter with 35 cm mic separation.

Interesting, where did you see that ?

I used the standard Jecklin disk (30cm/17cm) and found the stereo separation very usefull and sufficient, but I dropped this technique for recording concerts because of the not always good acoustics and the weight of the disk which made my high stand unstable. But I had great result on organ recordings.

JM

[George Necola]

I will meet him in 2 weeks.. I can ask mr. Jecklin what the reason is.. ;)

cheers

[Petrus]

2 weeks are up. The answer?????

[George Necola]

nothing. I suck.. I missed the date.. I try to get his email..

he is living most of the time in Vienna now and teaches..

will do my best..

[big country]

Originally Posted by George Necola

I will meet him in 2 weeks.. I can ask mr. Jecklin what the reason is.. ;)

cheers

wow how cool is that!

[George Necola]

wy? he is an old man, swiss inhabitant and we know each other from exebitions..

usually you can watch him walking very fast on the hallways (trough an exebition), because if he stops, people start talking to him...

3 years ago at the tonmeister conference in Leipzig he made it like 100 meters in 3 hours..



poor guy

[boojum]

George, did you ever catch up with Herr Jecklin and get the answer of why he doubled his separation from 17 to 35cm?? I am sure curious. And my chances of seeing him in the hallway are slim and none. More likely the latter.

[studer58]

Originally Posted by boojum

I never tried the narrower spacing. Jecklin already did the comparisons. He likes the wider spacing. ;o)

I am rigging a setup with the 12" disc, covered with foam and then that covered with faux lambs wool and adding a set of DPA 4006 TL's. Jecklin used these in his design so I am hopeful of stellar results.

Again, I would go with the 35cm. It has been tested; I trust Schweiz Rundfunk.

I also have a 12" disc and plan to use the 8020 omnis, but in reading through the original Jecklin manuscript I notice he recommends using diffuse field equalized mics rather than 'flat' ones. I imagine this would be quite significant as many users say that they like using the disc because they can afford to place it further away from the performers and still get a pleasing direct to ambience ratio pickup versus using comparable A-B spaced pairs ? Perhaps the use of diffuse field mics contributes to this ability to work at a greater distance ? I wonder if I'd be able to generate a similar HF response lift at the mic by using a 'pressure build-up ring' similar to the MKH-20, or even 30- 40mm sphere balls ?

Is there any consensus on how thick the disk should be, with the base plate plus foam padding and sheepskin ? I think mine is likely to be around 3 centimetres when it's finished....and I'll be mounting mine on a 35 cm spacer bar to match the disc diameter. Finally, is it desirable or essential to mount the mics centrally across the disc diameter, or is some amount of offset (forward/back) helpful in getting convincing imaging ?
Thanks for your help.

[Audiop]

Originally Posted by studer58

I wonder if I'd be able to generate a similar HF response lift at the mic by using a 'pressure build-up ring' similar to the MKH-20, or even 30- 40mm sphere balls ?

Interesting question which I have been thinking on as well. Using a ball you would increase the on axis response but at the ssame time decrease the amount of HF picked up at the back hemisphere of the mic, possibly not changing the power reponse at all.

Another approach would be to simply us EQ to open up the mic's in post.

The low noise of the mic's may let you get away with this. If the end result becomes more or less noisy than by going with a dedicated diffuse filed omni I don't know. The KM183 is a nice alternative.


/Peter

[boojum]

OK, here is where I am with the pursuit of the Snark, err, I mean Jecklin. LP record covered with 1/4" foam on each side and then covered with faux lambs wool. It is about 1.5 inches thick or 3.8cm.

I used the 4006 TL's with the trapezoid grids to roll of the highs at ~12 - 15KHz, the DD0254 rather than the diffuse grid, the DD0297. I am doing this because I am going to be right above the chorale director's podium (textbook placement) and the chorale's sopranos are not all smooth. So, DPA fixes this for me. I tried it at a lower height and the sound was good but not enough "room" so it is going back to the textbook height.

A work in progress.


NB - The paper which describes the 35cm placement of the mics also shows the mics to be parallel to each other and the disc, not angled outward with the diaphragms at the desired distance as in the 17cm arrangement.

[studer58]

Originally Posted by boojum

OK, here is where I am with the pursuit of the Snark, err, I mean Jecklin. LP record covered with 1/4" foam on each side and then covered with faux lambs wool. It is about 1.5 inches thick or 3.8cm.

I used the 4006 TL's with the trapezoid grids to roll of the highs at ~12 - 15KHz, the DD0254 rather than the diffuse grid, the DD0297. I am doing this because I am going to be right above the chorale director's podium (textbook placement) and the chorale's sopranos are not all smooth. So, DPA fixes this for me. I tried it at a lower height and the sound was good but not enough "room" so it is going back to the textbook height.

A work in progress..

I went back to the Jecklin document and couldn't find any direct references to mic height or placement, apart from suggestions that it's easier to place than A-B omnis or ORTF cardioids, so I'm curious about which 'textbook' you're drawing upon here ?

Originally Posted by boojum

NB - The paper which describes the 35cm placement of the mics also shows the mics to be parallel to each other and the disc, not angled outward with the diaphragms at the desired distance as in the 17cm arrangement.

I wondered about this also, as his diagram clearly shows a pair of omni mics pointing straight ahead with the baffle between them at 36 cms spacing, but can anyone translate his final sentence, which reads:

"Der Oeffnungswinkel beträgt rund 60° (Grund: Ueberhöhung des Frequenzgangs in der Mikrofonachse)" .... ???

In response to my own question about the alignment of the mic pair off-disc centre, I'm unsure whether Jecklin would have modified his 36 cm width instructions, compared with the 17cm spacing version, which states ". Take care that the microphone capsules on both sides are located at a distance of approx 8 cm directly above the disc center. " (copied from the Josephson site).... ???

Feeling like an archaelogist, and the inventor is still with us, as far as I know......

[boojum]

"The opening angle is about 60 [degrees]."

"Reason: rise in the frequency response of the microphone axis"

The pic shows the mics parallel. I will find the PDF and attach it in a mo'.

The "textbook" I am speaking of is the "textbook" plaement of a pair of mics above the conductor/director and aimed into the chorale/orchestra. It is common to the books on mic placement as a standard approach. It works well almost always and is not a "smoke and mirrors" setup; it is plain vanilla. How's that for mixing metaphors? ;o)

OK, found it and attached it. It is on page 30, 10.2.2. I am going by the pic. My German is over 50 years old now. If it were not for Google I would not have the translations above. ;o)

[studer58]

Thanks Boojum,

Indeed the "behind conductor and 9 to 15 feet up" is so common and useful a starting point as to be textbook after many decades...it's certainly my preferred main pair location ! Indeed J.Jecklin also suggested it in his initial notes to the smaller spaced (16-17cms) disk pair. At 36 cms spacing with omni mics I doubt very much whether straight ahead or angled placement of the omnis is going to make a lot of difference...except for altering the on or off axis behaviour a little ? I suspect the 60 degrees could pertain more to a pointing up/down angle from horizontal rather than a divergence from straight ahead/ parallel to the ground ? In that sense you could favour or discriminate against the front of a choir or orchestra compared with the rear...depending upon the off axis behaviour of your omni pair ? Thank you for the translation...I was wondering if it was a 'hangover' from his earlier (17 cms spacing) notes, because in the photos of commercial disks from Josephson and other makers you often see the mic bodies splayed out at around 60 degrees ? Well I have my sheepskin...now need to get some glue...is a dead central position with respect to the width of the disc the best placement for the mic diaphragms ?

[boojum]

@studer58: My German is very weak so I depend upon the pics in the Jecklin paper. I hope they are supported by the text. Perhaps someone who speaks German can help us out.

I place the diaphragms alongside the center of the disc. The diagrams indicate this as the proper spot as does the Josephson photo of their disc.

The next test I do I will run them with the trapezoids and the diffuse field (black) grids for a test. As this grid was intended for further back than where I am recording I do not think it will work well, especially having that boost, ~15KHz, where I am looking for an attenuation.

After I get settled in with this rig I think I will start using it more. I do like the sound it has, so far. ;o)