'figure 8' from 2x cheap SDCs?

Probably a nutty idea. I need a compact figure 8 for M-S in a blimp.

My GS has some Behringer B5s for $30 ea.  I'm guessing they use the Schoeps -type circuit, similar to MXL603, etc(?)  My idea is to  gut them and stick the two cardioid caps back-to-back in a light alloy housing, and reconfigure the electronics from one or both preamps to suit.

Any ideas on the best way to connect the two caps to one or both circuits, and end up w/ a useable fig 8?

(PS-any ideas what the  schematic for the Octavia 'figure 8 adaptor' might look like?)

thanks
Dave

Hello,
If You mean this Capsule for the  Octava , it s a  real completly  open Velocity Capsule with a mechanical resulting fig of 8  Pattern, no electrical  Arrangement is used .
If a Capsule is completly closed, airtight ( only a tiny Hole  to balance the Athmospheric Pressure Difference )You have a Pressurecapsule with Omni Pattern, half open results in a Velocity Cardiod Characteristic, completly open  create a Velocity fig of 8 Pattern.
Have a look here to see the open Back of the Capsule
http://www.oktava-shop.com/MK-012-100-Series-Baukastensystem/Kapseln/MK-012-fig-8-Kapsel.html?XTCsid=6fsovqt7fu9e2a341v53ic1034
If You use two seperate Cardiod Capsules Back to Back, You have two seperate Backplates  that could be Biased like the Neumann U 87 ( not 87 a/87ai ) ,have a  look  here
http://groupdiy.com/index.php?action=dlattach;topic=44805.0;attach=7892
The Downside of Your Idea might be that Phaseissues and Compfiltereffects  appear, If the Capsules are too far away from each other.  1  to 1,7 cm may be ok to  avoid this (1,7 cm= Wavelengh of 20 kHz at 20 Degrees Celsius )
It also would be good If the Capsules are matched for Output and Frequencyresponse.,to get a straight fig of 8 Pattern.
Greatings
Lothar
Edit, I just saw this Adapter You probably mean.
http://www.oktava-shop.com/MK-012-100-Series-Baukastensystem/Kapseln/MK-012-fig-8-Adapter.html
for  two Cardiod Capsules probably phasereversed connected. ( Membran. 1 at 0 Volt, Backplate 1 at 48 Volt, Membran 2 at 48Volt, Backplate 2 at 0 Volt )

Hi Lothar, and thanks for your reply.

Yes, I see what you mean. That one is a much better fig 8 capsule of course. I was thinking of this one
:
http://recordinghacks.com/microphones/Oktava/MK-012

Anyway, now I missed out on the 2x B5 deal, my backup plan: 2x back-to-back electrets 8>/ Well, until I can afford MKH30(!)

thanks again
Dave

Hello Dave,
Maybee this cheap , but quiet good Cardiod Mic discussed here could be a Alternative.You can buy them as matched Pairs for  less than 100 Bucks. You could use the Capsules and DIY a Adapter.
http://groupdiy.com/index.php?topic=57593.0
Greatings
Lothar

Yes, I see a very similar one available for $35US each, shipped from China.

('Cheap-but-good' mics are a terrible addiction!)

Re fig 8, assuming a 'Schoeps-style' circuit, what would the wiring look like to accomplish this (similarly to the 2x cardiod Octava)?

cheers
Dave

Hi Dave,
Have a look at the U 87 Capsule Arangement for fig of 8. i think If Membran 1 is at 0 Volt,  Backplate 1 at 48 Volt , Membran 2 at 48 Volt and Backplate 2 at 0 Volt. Now You Need to ac connect Membran 1 with Membran 2 and ac connect Backplate 1 with Backplate 2 . Dc  needs to be blocked  with a Capitor of 5/10 Nanofarad . I am not 100%  sure If You bias  Backplates and Membrans together  or seperatly with a high Value Resistor  at witch  the Voltagedrop and Rise You want to amp happens. I hope Somebody with more Skills can confirm or explain how it should be  done. I am far away to be an Expert, unfortunately.
Greatings,
Lothar

tubestation said:

Hi Dave,
Have a look at the U 87 Capsule Arangement for fig of 8. i think If Membran 1 is at 0 Volt,  Backplate 1 at 48 Volt , Membran 2 at 48 Volt and Backplate 2 at 0 Volt. Now You Need to ac connect Membran 1 with Membran 2 and ac connect Backplate 1 with Backplate 2 . Dc  needs to be blocked  with a Capitor of 5/10 Nanofarad . I am not 100%  sure If You bias  Backplates and Membrans together  or seperatly with a high Value Resistor  at witch  the Voltagedrop and Rise You want to amp happens. I hope Somebody with more Skills can confirm or explain how it should be  done. I am far away to be an Expert, unfortunately.
Greatings,
Lothar

Click to expand...

(edit) I checked the U87 schematic, and I see what you're talking about. You may be able to do something like that.  It's possible that two preamp circuits might be needed to get each capsule to function properly, and then at some point (either at the capsule's output, or further along), arrange the circuit so it would output the  two opposite-polarity signals to a single balanced output. Probably simple enough, but with these cheap mics there are usually no schematics to go by, which doesn't help.

Dave

Dave,
I am quiet sure that both Capsules can  drive one Amp because it s  done in the U 87/ Ela My 251 where two Membrans and two isolated Backplates  work together to create the different Pattern.  I wonder what  happens If You  just  disconnect one Capsule from one Mic, apply the Biasvoltage to both Capsules as disired for the Pattern of fig 8, connect BP 1 with BP 2 with a 10 Nanofarad Capitor, Membran 1. with Membran 2 with a 10 Nanofarad Capitor and reconnect this Array back to the Micamp  at the same Position where the single Capsule was  connected before. Maybee it is that easy.  Maybee I am wrong....
I hope Somebody can help, because I think it could be a good Idea to build a small Diagramm Condenser fig 8 like this, there  aren t too much Mics like this on the ( Budged) Market. Mkh 30 and Shoeps Colett are  really great Mics  with a  real fig 8  open Back Velocity  Capsule  but  ....... pricey.....
Greatings
Lothar

So what you're saying is, connect the second capsule  to the same two (bias voltage) points in the circuit as the existing capsule, but  in reverse polarity (that would give you the 48/0/48/0V biasing), but tap off the audio from the second one through a coupling cap...  then where will that go? Sounds like a whole new circuit might be needed (not that it couldn't be fairly simple).
I think I have the Schoeps schematic somewhere from when I modded some MXL603s, I'll have a look...

It really would be nice to see  people doing more SDC stuff here, and more figure 8>]


Dave

Hello Shaggy,
I mean If I connect Backplate 1 (48 V ) with  Backplate 2. (0V) and Membran 1 (0V ) with Membran 2 (48V) it must be done through a Capitor to block dc. Without the Capitor i would have create a heavy Short .
Ac can pass, dc is blocked.
( Dc 48 Volt goes to Backplate 1 and Membran 2 , 0 Volt to Backplate 2 and  Membran 1 ) If I connect this Array now to the same Place, the Single Capsule was connected it could work and result in a Pattern of Eight. The Soundwave that reach both Capsules at 90/270 Degrees have the same Timing and Level, so get  canceld  due to the summing of the two Phase  reversed Signals, at 0 / 180 Degrees  , Timing and Level  are different, so no canceling  when the two phasereversed  Signals ,coming from both ac connected Capsules , are summed.
I try my best to understand but it would be great If Somebody could confirm or correct my Thoughts, i hope that this what this Place is about. Somebody has a Theory that is eventually wrong or Nonsens , more enhanced People explain and correct it, If it s not the absolutly Bull S...., If so , i can t hope for  an  Answer.
That s why I post here, to learn something and to try to  give something ( for me the only Reason , because I own enough Mics and Gear )
Greatings
Lothar

tubestation said:

I  own enough Mics

Click to expand...

you never, ever own enough mics

More on topic: You idea makes absolutely sense. It should work like that.
Of course, a consideration to be made is that self noise will be doubled by having two capsules summed together.

"I mean If I connect Backplate 1 (48 V ) with  Backplate 2. (0V) and Membran 1 (0V ) with Membran 2 (48V) it must be done through a Capitor to block dc. Without the Capitor i would have create a heavy Short .
Ac can pass, dc is blocked."

Got it.

( Dc 48 Volt goes to Backplate 1 and Membran 2 , 0 Volt to Backplate 2 and  Membran 1 ) If I connect this Array now to the same Place, the Single Capsule was connected it could work and result in a Pattern of Eight.

OK...

The Soundwave that reach both Capsules at 90/270 Degrees have the same Timing and Level, so get  canceld  due to the summing of the two Phase  reversed Signals, at 0 / 180 Degrees  , Timing and Level  are different, so no canceling  when the two phasereversed  Signals ,coming from both ac connected Capsules , are summed.

Yes. I think.

I try my best to understand but it would be great If Somebody could confirm or correct my Thoughts, i hope that this what this Place is about. Somebody has a Theory that is eventually wrong or Nonsens , more enhanced People explain and correct it, If it s not the absolutly Bull S...., If so , i can t hope for  an  Answer.
That s why I post here, to learn something and to try to  give something ( for me the only Reason , because I own enough Mics and Gear ) ..."

Agreed. Expert verification would be useful (hint hint).

Back to my schematics/scribblings...and further digestion.

I'm sure it's not too difficult!

best wishes
Dave

shaggy said:

Probably a nutty idea. I need a compact figure 8 for M-S in a blimp.

My GS has some Behringer B5s for $30 ea.  I'm guessing they use the Schoeps -

type circuit, similar to MXL603, etc(?)  My idea is to  gut them and stick the two cardioid caps back-to-back in a light alloy housing, and reconfigure the electronics from one or both preamps to suit.

Any ideas on the best way to connect the two caps to one or both circuits, and end up w/ a useable fig 8?

Click to expand...

Place two capsules one above another, keeping the diaphragms in the same vertical plane. In principle, you could place those capsules ala Octava (i.e. back to back), however, you will get more phase, frequency, and polar pattern anomalies. Make sure the capsules physically do not touch each other to avoid shorting. Connect capsule criss/cross (i.e. body of one to backplate of another) and then to the input of the head pre. You will need to shield this structure with mesh to get rid of hum.

In principle, if you connect both backplates and bodies in parallel you will get more or less omni.

Best, M

tubestation said:

If You mean this Capsule for the  Octava , it s a  real completly  open Velocity Capsule with a mechanical resulting fig of 8  Pattern, no electrical  Arrangement is used ...

half open results in a Velocity Cardiod Characteristic, completly open  create a Velocity fig of 8 Pattern.

Click to expand...

While some older sources call such condenser capsules "velocity" those actually are "pressure-gradient" ones. The term "velocity" is reserved for mass controlled  fig-8 ribbon microphones, to stress that their response reacts to velocity of air particles (or soundwave forces).

Best, M

Marik said:

shaggy said:

Probably a nutty idea. I need a compact figure 8 for M-S in a blimp.

My GS has some Behringer B5s for $30 ea.  I'm guessing they use the Schoeps -

type circuit, similar to MXL603, etc(?)  My idea is to  gut them and stick the two cardioid caps back-to-back in a light alloy housing, and reconfigure the electronics from one or both preamps to suit.

Any ideas on the best way to connect the two caps to one or both circuits, and end up w/ a useable fig 8?

Click to expand...

Place two capsules one above another, keeping the diaphragms in the same vertical plane. In principle, you could place those capsules ala Octava (i.e. back to back), however, you will get more phase, frequency, and polar pattern anomalies. Make sure the capsules physically do not touch each other to avoid shorting. Connect capsule criss/cross (i.e. body of one to backplate of another) and then to the input of the head pre. You will need to shield this structure with mesh to get rid of hum.

In principle, if you connect both backplates and bodies in parallel you will get more or less omni.

Best, M

Click to expand...

Thanks Marik--It doesn't get much simpler than that, eh  ;D (The extra capacitance is not a problem for the input stage?)

I'll probably try this with a pair of MXL 603s (I believe those cardioids have a pretty wide pattern, for what that's worth M-S wise). 
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.

cheers
Dave

Dave

Hello Marik,
Thank s for clearing  and chiming in .
I mean the same, in German it s  called Druckgradienten Empfänger  , so i tried the Translator that gave me this Translation, my Jargon could be better.....
Interesting  that the Definition Velocotycapsule is reserved or true for Ribbons only.
Was my Concept  with the Arrangement  of the 2 Phasereversed Capsules  technical correct ? To ac connect the phasereversed Capsules with  two 10 Nanofarad Capitors ?

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.
I own a RCA D 77 Ribbonmic that is mechanical adjustable as well. Even different Presence Behaviors are possible to adjust, very usefull.
Greatings
Lothar

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.

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...

Hi Ricardo. I have some TSB165As I've been wanting to do something with (initially had them in mind for this fig 8 using the Naiant X-8 circuit). In any case, I look forward to reading your paper.

thanks
Dave

Hello Ricardo,
Thank You very much !
I am looking forward to read Your Paper.
I was thinking to join the Yahoo Micbuilders for a  long Time, i hesitated because You need a Yahoo Account and i am very picky where to join ( no Facebook, YouTube. etc, )  now I have a good Reason to join and to jump over my Shadow ( as we say in Gemany )
Greatings,
Lothar

Marik (quote) "Place two capsules one above another, keeping the diaphragms in the same vertical plane. In principle, you could place those capsules ala Octava (i.e. back to back), however, you will get more phase, frequency, and polar pattern anomalies. Make sure the capsules physically do not touch each other to avoid shorting. Connect capsule criss/cross (i.e. body of one to backplate of another) and then to the input of the head pre. You will need to shield this structure with mesh to get rid of hum.

In principle, if you connect both backplates and bodies in parallel you will get more or less omni. "



Hi Marik and guys. Here's progress from tonight, using my MXL603s. Capsules are mounted flat either side of 2mm Teflon sheet, perforated to keep the backplates open, and mounted in a threaded adaptor.  Caps are staggered front to back (by 6mm) rather than vertically, as I need minimum height. I trust this will have minimal effect on coincidence. 
Note the backplate perforations expose directly to the opposite side, as opposed to Octava fig-8 adaptor in-line caps, which are farther apart and have the perforations between them, arranged in the vertical plane.
As you (Marik) already suggested, with reduced shielding, and the right side capsule casing 'live' (connected to diaphragm of left cap) a mesh enclosure will probably be required. More progress tomorrow... 


Dave