'figure 8' from 2x cheap SDCs?

shaggy said:

I doubt there's enough space in the blimp (~4") to arrange the caps vertically, but I believe I can get them to go back-to-back quite a bit closer together than the Octava adaptor has them.

Click to expand...

If you decide to do it that way remember to leave some space between capsules for the soundwave to reach back of the capsule. If you look to the original 603 body you will see machined slits. You will also find a plastic diffuser--both of those form a certain pattern/freq response of the capsule.

Make a plastic (insulating) coupler tube and drill around it series of holes. With changing their diameter you can to some degree control freq response and pattern.

tubestation said:

Was my Concept  with the Arrangement  of the 2 Phasereversed Capsules  technical correct ? To ac connect the phasereversed Capsules with  two 10 Nanofarad Capitors ?

Click to expand...

While you could do it that way it complicates the DC converter schematics. To flip the capsule connection is much easier and you could use any available head pre without modification.

Only a few , like some Shoeps Capsules  are mechanical  adjustable. closed for Ommni, Real  Pressureomni,    half open, Pressuregradient Cardiod,    completly open,  Pressuregradient Fig of 8 . These Capsules  are a Dream, the Buildquality is like a expensive Swiss Watch. The mechanical Precion is unbelievable.

Click to expand...

Yes, those are very cool with marvelous engineering! Personally, I much prefer dedicated pattern capsules, as it is much easier to optimise them and for omni and fig8 use native responses, rather than make them resistance controlled.

I own a RCA D 77 Ribbonmic that is mechanical adjustable as well.

Click to expand...

In some situations that mic can be very useful for a certain tone. In general, the D77 doesn't have any solid pattern (not even fig8, which is way assymetrical). I cannot wait to see a newest Les' mic.

Best, M

tubestation said:

Was my Concept  with the Arrangement  of the 2 Phasereversed Capsules  technical correct ? To ac connect the phasereversed Capsules with  two 10 Nanofarad Capitors ?

Click to expand...

Quote Marik,

" While you could do it that way it complicates the DC converter schematics. To flip the capsule connection is much easier and you could use any available head pre without modification."

Marik,
Thank You very much for explaining !

Only a few , like some Shoeps Capsules  are mechanical  adjustable. closed for Ommni, Real  Pressureomni,    half open, Pressuregradient Cardiod,    completly open,  Pressuregradient Fig of 8 . These Capsules  are a Dream, the Buildquality is like a expensive Swiss Watch. The mechanical Precion is unbelievable.

Click to expand...

  Quote Marik,

" Yes, those are very cool with marvelous engineering! Personally, I much prefer dedicated pattern capsules, as it is much easier to optimise them and for omni and fig8 use native responses, rather than make them resistance controlled. "

After thinking a while I understand Your Statement that  mechanical adjustable Capsules are a Compromise.
A  real Pressure Omni Condensercapsule has a Diagram that is very tight and heavy stretched that results in a very high Resonantfrequency, outside the Audioband. That Results in a very linear and Bass strong  Frequencytransmission.
A Cardiod Pressuregradient  has a lower stretched  Diagram, tuned so that the Resonantfrequency is in the Middle of the Frequencyband. With  heavy  damping , with the Help  of the Aircussion between Diagram and Backplate including the Air that is present in the notthroughdigged Holes , Blindholes (acustical Resistance) the Frequencypeak get s tamped down that the Frequencyrespond is more or less linear.
What s the Case with a open Pressuregradient fig of 8  Condensercapsule ? How is the Diagram stretched ? Is it s  Selfresonance tuned very low , because of the completly open Backplate ? Or high, realised with stronger stretching , Tension ?
Thank s

I own a RCA D 77 Ribbonmic that is mechanical adjustable as well.

Click to expand...

Quote Marik,
"In some situations that mic can be very useful for a certain tone. In general, the D77 doesn't have any solid pattern (not even fig8, which is way assymetrical). I cannot wait to see a newest Les' mic."

I absolutly agree.  I always wondered about the assymetrical fig8. I thought the Mic is not in the best Shape.
I didn t use the Mic for natural sounding Recordings, but for the Vintage Characteristic  when placed infront of a Guitaramp, for Main or Backingvocals and as a  Drumroommic not too far placed from the Drums. I like the tight Bassresponce.
Thank s again ,
Lothar

Marik said:

shaggy said:

I doubt there's enough space in the blimp (~4") to arrange the caps vertically, but I believe I can get them to go back-to-back quite a bit closer together than the Octava adaptor has them.

Click to expand...

If you decide to do it that way remember to leave some space between capsules for the soundwave to reach back of the capsule. If you look to the original 603 body you will see machined slits. You will also find a plastic diffuser--both of those form a certain pattern/freq response of the capsule.

Make a plastic (insulating) coupler tube and drill around it series of holes. With changing their diameter you can to some degree control freq response and pattern. ...


Best, M

Click to expand...

Hi Marik. Did you see my picture (previous page)? Does it look like there is enough venting of the backplates through those holes and around the back of Teflon support? If necessary, there's the possibility of experimenting by moving the capsules in relation to each another and exposing  more (or less) backplate to venting.

I think(?) perhaps this staggering of the capsules, by exposing the backplates to some degree directly (line of sight) to the opposite-side sound source, has an advantage over 'inline' capsule setup (Octava), where venting is solely between the more widely-spaced capsules.

Actually, it seems that the staggering itself should not matter, since it would make little difference to the actual timing of Side sound sources arriving at each membrane, and with (hopefully) fig-8 pattern, response of both cardioids should be nulled  at 90 and 270 degrees in any case. The Octava's larger capsule spacing presents potentially greater coincidence error, I think.

(BTW, your suggestion of capsules one on top of the other with membranes aligned vertically is of course closest to ideal.)


Here is a pic of the other side.

David (shaggy)

ricardo said:

If anyone is interested in making a true single diaphragm Fig-8, I've a paper on the subject in my Yahoo MicBuilders directory.  You have to join.

You could do it with bits from 2 Transound TSB160 or 165 capsules.

Click to expand...

Ricardo, can you please provide a direct link to this paper, and the relevant discussions? I always have trouble finding anything at micbuilders 

PS--Never mind, I found it. Thanks.

David

Marik:

" ...  To flip the capsule connection is much easier and you could use any available head pre without modification."

[/quote] 

I am finding that this is easier said than done. Even with full coverage mesh screen grounded to the mic tube (there is zero hum) the reversed 'live' capsule casing is extremely sensitive to and/or is creating a huge amount of stray capacitance. There is almost nothing but constant loud crackles and pops that outweigh any audio signal (there is some audio output from both sides, though). Maybe I have the screen too close  around the caps (was maybe 2mm away, caps insulated by short rubber sleeves)? All connections were double checked, are tight and clean, and there are no shorts.
This seems quite a different exercise than, for instance, sticking a dual-diaphragm LDC in a housing, where the external capsule case connections remain floating (at least, not connected to mic housing) until exiting  the PCB as 'mic ground'.
What am I missing?

Dave

Hello Dave,
Do You have a internal Connection between the Capsulechasis and the Backplate or the Diagram ?
If in the original Configuration the Diagram was. 0 Volt, the Backplate at 48 Volt, You now have one Capsule ( the flipped One) where the Diagram is at 48 Volt. Now Your 48 Volt are lying on the Chasis, and the internal Wiremesh, in the Outside World. This could be  a Problem and a Reason for the Noise. Can You cut this  Connection of the Diagram with the Capsulechasis ?
Greatings
Lothar

I've got a AKG CK6 that does all this

tubestation said:

Hello Dave,
Do You have a internal Connection between the Capsulechasis and the Backplate or the Diagram ?
If in the original Configuration the Diagram was. 0 Volt, the Backplate at 48 Volt, You now have one Capsule ( the flipped One) where the Diagram is at 48 Volt. Now Your 48 Volt are lying on the Chasis, and the internal Wiremesh, in the Outside World. This could be  a Problem and a Reason for the Noise. Can You cut this  Connection of the Diagram with the Capsulechasis ?
Greatings
Lothar

Click to expand...

Hi Lothar. If I understand you, yes--the left diaphragm ('48 Volts') is connected to the right casing/backplate, and the right diaphragm is connected to the left casing/backplate ('0 Volts').  So the right capsule casing is now 'live/hot' and must be insulated and heavily shielded. 


Dave

shaggy said:

If I understand you, yes--the left diaphragm ('48 Volts') is connected to the right casing/backplate, and the right diaphragm is connected to the left casing/backplate ('0 Volts').  So the right capsule casing is now 'live/hot' and must be insulated and heavily shielded. 

Click to expand...

Not sure what do you mean by "casing/backplate". The capsule  casing is connected to diaphragm (and in original connection is at ground), and the stud on the back is connected to backplate. Did you check that both capsules are working properly?

Best, M

Hello Dave,
I mean that I don t know If it s ok If the Case, the Capsulehousing of the second ,reversed, Capsule is biased with 48 V .not sure If the Shielding is working as it should in this Case, and If You don t get Noise from this . You maybee create a Capitor with the other isolated Parts of Your Construction, but I am not 100% sure......, just an Idea.
If You are not sure If Your new constructed Headbasket shields good enough, You could place the Mic in a (or two ) closed solid Metalbox(es) ,  ( Steel or Brass , not Alluminium ) with a Hole diged for the Cable and listen If the Hum is gone or not. If the Hum is gone, You know that the Shielding of Your new Headbasket needs some Work.
Greatings,
Lothar

Marik said:

shaggy said:

If I understand you, yes--the left diaphragm ('48 Volts') is connected to the right casing/backplate, and the right diaphragm is connected to the left casing/backplate ('0 Volts').  So the right capsule casing is now 'live/hot' and must be insulated and heavily shielded. 

Click to expand...

Not sure what do you mean by "casing/backplate". The capsule  casing is connected to diaphragm (and in original connection is at ground), and the stud on the back is connected to backplate. Did you check that both capsules are working properly?

Best, M

Click to expand...

(duh) --Sorry, I meant... casing/diaphragm of one capsule is connected to backplate (center stud) of the other, and vise-versa.

Yes, both caps have good output and are noise-free in their respective preamps.

Here's pics of my adaptor, showing the means of interconnection, and (second pic) of insulating the casings from the mesh shield. I was fairly sure nothing was loose or shorting when it was assembled, there was no hum with the shield on. The mesh is stainless steel, and was bound tight to the copper adaptor barrel with stainless steel safety wire.  As I said, there was audio output from each side, besides the pops and crackles.
Probably in my attempt to make the thing as compact as possible, and haste to get it working, I overlooked something...

Dave

Insulating rubber... possibly mesh screen was too close to caps?

Dave

Hello,
So it is ok to have the 48V Biasvoltage at the Chasis and the internal ( the Original ) Wiremesh?
Is there no Leakage  or Discharge, , even if the Chasis is isolated with Rubber ?
It would be very nice if Somebody could answer my Question.
Thank s !
Greatings,
Lothar

tubestation said:

Hello,
So it is ok to have the 48V Biasvoltage at the Chasis and the internal ( the Original ) Wiremesh?
Is there no Leakage  or Discharge, , even if the Chasis is isolated with Rubber ?
It would be very nice if Somebody could answer my Question.
Thank s !
Greatings,
Lothar

Click to expand...

I assumed the answer was 'yes', but then look where that's got me(!)

But your question has made me think that I should probably check the actual insulation value of that 'rubber' (inner tube)!

And probably start all over again ... 

Dave

Update: I made another temporary headbasket big enough to safely clear the capsules, and (of course) now it works fine. No noise, and a healthy output from both sides.
The bad news is the headbasket has to be 1-1/2" wide to clear my capsule arrangement. So much for my 'compact' Fig-8 solution! 

(Over the weekend I also built a cardioid electret version of this, using Ricardo's 'SimpleP48' circuit. Very promising and isn't much bigger than the XLR connector it's built into. I'm going to try this with some high-end electret caps next... )

Dave

Update: Success! I made another mesh screen and replaced the insulation around the capsules. The noise is gone--there must have been a short there somewhere.

This thing sounds great in an M-S rig, and is (just) small enough to go in the blimp 

Next I want to figure out a simple way of testing the polar frequency response. Any ideas are welcome.

(thanks to Marik, BTW)

Dave