Microphone-parts RK12 variable pattern mikes in Oz?
« on: June 08, 2019, 02:43:37 AM »
Has anyone in Oz made a variable pattern mike with a Microphone Parts RK12 and would be willing to lend it to me for a couple of weeks?  I can promise at least a detailed report.

I made detailed measurements of Zephyr's CK12 mike (from WGT IIRC). The results are in Yahoo MicBuilders Files as Zephyr.pdf
https://groups.yahoo.com/neo/groups/micbuilders/files/Mic%20Measurements/
You have to join.  It's not bad but there are a few things which could be better ..  notably the fig-8 response.

There's some evidence that the Microphone Parts RK12 won't have this fault but I need to get my paws on a complete mike to confirm this.

Another capsule I'd like to look at (in complete variable pattern mike form)  is the Transound TSC-2 though this is a K67 type.  Not on the JLI website http://www.jlielectronics.com/  but available from  them for a phone call or email.

JLI are US agents for Transound and will ship small quantities anywhere in the world.

Eric Benjamin has measurements in Cardioid mode in the same MicBuilders directory above .. which suggest this doesn't have the slightly wonky fig-8 response either.
« Last Edit: June 08, 2019, 04:19:53 AM by ricardo »


ln76d

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #1 on: June 09, 2019, 05:40:55 PM »
Hello Ricardo,

nice to have you back here ;) 
I didn't saw you for a while (ok i wasn't here also for a while ;) )

Could you post schematic of the mic here or give some link where there's no need to create account?
Also measurement here as attachment would be helpfull.

BTW. what is Oz? I think rather you don't have in mind Wizzard of Oz :D

Khron

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #2 on: June 09, 2019, 06:29:50 PM »
https://en.wikipedia.org/wiki/Name_of_Australia#Oz ;)

BTW. what is Oz? I think rather you don't have in mind Wizzard of Oz :D
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #3 on: June 09, 2019, 07:32:19 PM »
Could you post schematic of the mic here or give some link where there's no need to create account?
It's really the capsules I'm interested in though the circuit in Zephyr's mike is also interesting as its a variant of Guru Scott Wurcer's Charge Amp circuit.

This is the set of Fig8 responses in 8 directions.  There are another 2 sets for Omni & Cardioid.  Also 2 noise spectrum plot sets with up to 14 measurements each.

There's too much info to put in a post.  If this is important to you, join MicBuilders & download the file.  It has a couple of pages of explanation.

I continually update the copy on MicBuilders with new info/measurements so it is always current.

Wizard ricardo  ;)
« Last Edit: June 09, 2019, 07:40:49 PM by ricardo »

ln76d

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #4 on: June 10, 2019, 02:56:34 PM »
Passed with yahoo account when they forced me to  give phone number.
Rudolph came with help, he sent me document. Anyway there's hard talk about the microphone and capsule when i don't see how the capsule is connected.
Maybe this would be to obvious, but doesn't harm to ask - are you sure that you have full continuity between backplates and the circuit? These capsules sometimes have connected both backplates to eachother inside (via metal shim) and sometimes isolated). Not always there's proper connection between backplate wire and backplate. For now i had only one such capsule where there was no backplate connection on one half.

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #5 on: June 10, 2019, 04:45:05 PM »
Anyway there's hard talk about the microphone and capsule when i don't see how the capsule is connected.
Maybe this would be to obvious, but doesn't harm to ask - are you sure that you have full continuity between backplates and the circuit? These capsules sometimes have connected both backplates to eachother inside (via metal shim) and sometimes isolated). Not always there's proper connection between backplate wire and backplate.
Not sure what you are suggesting Do you think wonky fig8 response is due to bad connection?

The measurements in 8 directions for each pattern show what is expected for a properly connected capsule in variable pattern mike

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #6 on: June 10, 2019, 05:46:32 PM »
the circuit in Zephyr's mike is also interesting as its a variant of Guru Scott Wurcer's Charge Amp circuit.
Actually the Wurcer Charge Amp variants are on two 25mm cardioid electret capsules measured on the same document; the Rayking 'blues' and the excellent Transound TSB2555.  The circuits are by Zapnspark who calls his Wurcer Charge Amp variants Occam

Zephyr's CK12 clone uses Zap's S2PCM circuit which is 2 'Schoeps' circuits, one for each diaphragm, with the outputs mixed as needed to produce Omni, Cardioid & Fig8.  Zephyr helped him correct a noise problem and also made the patterns continuously variable.

Zap's circuits are in his MicBuilders/Files directory.
« Last Edit: June 10, 2019, 06:05:56 PM by ricardo »

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #7 on: June 10, 2019, 05:50:14 PM »
I measure each of these circuits & discuss the implications for noise performance but this thread is actually about CAPSULES.

I used to design capsules & mikes for Calrec.  The Mk4 Soundfield was my baby.  I have never designed a Double Diaphragm capsule but this exercise has got me itchy to resurrect some nearly 40 yr old skills.

True AKG CK12 has had many changes & variants over the years but what I'm trying for is what Bernhard Weingartner, who did the original, was after.  Most C414/12 & their clones are used for multi-miking/ tracking these days and a good Cardioid makes most users happy.  The 'so called' HF lift of C12 is part of this scene

But in dem days, Fig8 was really important for eg Broadcasting the Proms from the Royal Albert Hall using Blumlein crossed Fig8s ...  and Bernhard was after a 'flat' response.

The CK12 clone I measured is good for Cardioid .. as are most other CK12 clones.  But Fig8 could be better.

A clone using K67/87 backplates, like Zephyr's, could be designed & made to do this simply.  I'm unlikely to leave my beach bum life to ever confirm this ... but it means there must be CK12 'clones' and/or K67/87 capsules which are close to this target.

Hence my interest in Microphone Parts RK12 and the Transound TSC-2

ln76d

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #8 on: June 10, 2019, 06:11:31 PM »
Not sure what you are suggesting Do you think wonky fig8 response is due to bad connection?

Not bad but lack of connection on one half of backplate if these aren't connected to eachother internal. Not really interested in this circuit, just wasn't sure what we are talking about.  I'm assuming right that this is 2x schoeps topology mix fed from single dc converter to both backplates?
Checking both backplates connection is just an idea, i don't insist that this is a cause but as i wrote - i had one capsule where one backplate had no onnection with wire (i had to cut off a little teflon insulator and tighten the screw).
One other option to try with the capsule - check the shims between both halves. These capsules can have different variants of shims. These which i saw - single ultra thin plastic, double ultra thin plastic, thicker metal shim.
If you have some spare 34mm chinese made k67 with the same screw pattern as "Ck12", you can borrow shim from it to test.
Many have exactly the same size of shim and in fact all these CK12 clones are nothing more than just edge terminated k67.
Worth to try change gap between backplates ;)
Original CK12 also have this similar backplate holes pattern (so called teflon CK12 holes pattern fits exactly most 34mm k67 for example)  but it is chambered design.

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #9 on: June 10, 2019, 11:04:20 PM »
Not bad but lack of connection on one half of backplate if these aren't connected to eachother internal.
If that was the case, the front & back responses of the Fig8 & Omni patterns would be different and noise would be high.  The measurements show impressive matching & very good noise for these.

Quote
One other option to try with the capsule - check the shims between both halves. These capsules can have different variants of shims.
As a matter of fact, this is one of the things to vary if I was trying to redesign this capsule to have flatter Fig8 response.

But its more complicated than just doing that.  There are other factors.  You have to ensure the Omni & Cardioid responses don't go out of whack when you 'improve' the Fig8 response.  That's 24 measurements to check out each change.  8)

These are not my capsules & mikes so I'll leave them alone & just measure them properly.


ln76d

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #10 on: June 11, 2019, 05:22:01 AM »
If that was the case, the front & back responses of the Fig8 & Omni patterns would be different and noise would be high.  The measurements show impressive matching & very good noise for these.
As a matter of fact, this is one of the things to vary if I was trying to redesign this capsule to have flatter Fig8 response.

Not necessary, but depends on the capsule and its connection. With this particular one i had Omni and Cardioid worked fine figure of eight was problematic. 

But its more complicated than just doing that.  There are other factors.  You have to ensure the Omni & Cardioid responses don't go out of whack when you 'improve' the Fig8 response.  That's 24 measurements to check out each change.  8)

These are not my capsules & mikes so I'll leave them alone & just measure them properly.

I don't say it's only thing, but this one is the easiest to check.  Matter of four screws and definately something worth to try even out of curiosity ;)

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #11 on: June 11, 2019, 04:12:41 PM »
Not necessary, but depends on the capsule and its connection. With this particular one i had Omni and Cardioid worked fine figure of eight was problematic.
What problems did you see with the Fig8 when wrongly connected ?  Got any response measurements ?
« Last Edit: June 11, 2019, 05:22:24 PM by ricardo »

ln76d

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #12 on: June 14, 2019, 05:09:07 AM »
There was unproper polar pattern with big tendency to omni shape if i remember correctly, midrange dip (don't remember exact frequency range) and sensitivity was lower than it should. I need to search in more free time for these measurements i should have at least paper prints, files rather lost with laptop. If i will find it i will post it here.
« Last Edit: June 14, 2019, 05:12:57 AM by ln76d »

Re: Microphone-parts RK12 variable pattern mikes in Oz?
« Reply #13 on: June 17, 2019, 04:20:13 AM »
Thanks for the clarification.

Zephyr's mike hasn't got any of this stuff.  My measurements show
  • Directivity is impressively Fig8
  • there is a midrange peak
  • Sensitivity is exactly as I'd expect from the capsule design and the circuit


 

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