Omni - Cardioid Conversion For M7 Condenser Capsule

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rodabod

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Joined
May 12, 2005
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Hi,

Can anyone explain why my "lower quality" M7 condenser capsule acts as an omni directional when it only has one spring electrode on one side?

I wrote about it in the last post here:

http://www.groupdiy.com/index.php?topic=8766&start=15

The capsule looks like this:

reissmann32nv.jpg


I was under the impression that there would need to be an electrode on each side of the capsule to provide an omni pattern (ie. both sides summed).

This casule only has a spring electrode on one side, yet the other side without an electrode picks up just as much volume with a little less treble.

How could I make this capsule cardioid, or is it not possible?

Thanks,

Roddy
 
Is it in a sealed chamber? If the back of the capsule is not "open air" or a reasonable approximation, it will be omni-ish, like an omni SD mic.
If not, it could be the back of the capsule itself is somehow sealed, not even in a chamber in the mic, and so designed to be omni all the time. Show us a pic of the back. If that is the case it will probably be really hard/impossible to make cardioid because you'd have to screw with the design of the capsule and probably change the sound a lot even if you succeed without destroying it...
 
The other side of the capsule looks exactly the same as the side pictured, except it does not have a spring electrode connected to it.

The capsule is currently mounted in a Chinese large diaphragm condenser.

So, is it likely that the capsule will always be omni? Is it because the capsule is sealed at the other side?

What is the difference between this and another dual diaphragm casule?

Are other dual diaphragm capsules vented on both sides?
 
That's about all I know unfortunately. I'm curious to see what the answer will be when others chime in here; I bet it's rather simple.
My best guess is that perhaps the back diaphram is tensioned much higher than the front, which makes the front behave as a pressure gradient (??)


I'm probably way, way off base here.
As a side note that is probably the weirdest capsule I've ever seen. Does it sound good?

Edit: Read your latest in the other thread... so it sounds good, that's a plus... are you sure it's omni and not figure-8?
 
What you're describing doesn't sound like an omni pickup pattern. All cardiod capsules allow a good deal of sound ( mostly bottom end) to come through the rear of the capsule. How much sound does the capsule recieve when you place the sound source facing the side of the capsule? If the capsule sounds normal when speaking in the front membrane, dark when speaking in the back membrane and recieves very little sound when speaking to the sides of the capsule then it's cardiod. An omni capsule would sound almost the same no matter where you spoke into it and in reality wouldn't let any sound reach the back of the membrane.

It would be easier to build a whole new cardiod capsule than to convert a true omni to cardiod. A dual membrane omni is actually the combination of two cadiod patterns.
 
[quote author="dasbin"]
As a side note that is probably the weirdest capsule I've ever seen. Does it sound good?[/quote]

Yeah, it does sound good, although it is being used in a so-so Chinese microphone. It is quite bright, more mid-rangey than the Chinese capsule, but it is in omni mode, so it is hard to compare. It may be made by Neumann. All I know is that it is a "lower quality" M7.
 
[quote author="Tim Campbell"]What you're describing doesn't sound like an omni pickup pattern. All cardiod capsules allow a good deal of sound ( mostly bottom end) to come through the rear of the capsule. [/quote]

This is more true if you are really close to the capsule though... if the back gets much quieter when you back off a few feet, then it's cardioid.
I have a feeling this may be some weird figure-8 configuration though. I'm trying to think through the physics in my head and my only hypo is that the back membrane is causing the front to sympathetically vibrate, which would create a sort of psuedo-figure-8 (out of phase to the front) but definitely with less top-end as you describe.

Anyway I will shut up and stop bloating this thread with useless guesses until someone who knows more chimes in.
 
Ok, I've just tested it again.

The sensitivity remains constant all around the microphone until on axis (0 degrees) where the level increases a little (say, 3 dB) and there is an increase in top-end.

Even at 90 degrees, the sensitivity is the same as the rear side.

It does not sound to me like a cardioid. One guess (from me) is that it might be an omni, but the rear diaphragm is not working as well as the front one.
 
What you're describing is a cardiod pattern. Think of a cardiod pattern as a figure 8 pattern with one very efficient functioning side and one very poor functioning side. If your capsule has an extreme amount of sound reaching the back it may just be poorly designed

Iimagine that you were to take a sigle diaphram omni capsule and start opening small holes through the back of the capsule . Soon you'd end up with a cardiod pattern capsule. If you continued you'd get a super cardiod pattern and eventually you'd end up with a figure 8 pattern. It's actually more complicated than this but this is a good way to envision it. Check out Sony's C37 capsule and some of Shoeps multi pattern capsules.
 
some cardiods capsules can be more to the omni or more to the 8. walk around the microphone talking or clicking your fingers with a earphones on and check the pattern. Some time capsule patterns change with freg one pattern at the highs one at the lows.

I think my M7 sounds more towards the 8 when used with my gefell 692 and set to cardiod. I believe I read that often the u49 would have its pattern set a little more to omni side of the center for cardiod use with voice.
 
Thanks guys,

I've listened to it yet again and it still sounds omni to me (even though it may be a cardioid).

The sensitivity at 90 degrees is more or less the same as the rear (180 degrees). Strange.

Myabe I should just leave it as it is.

I am happy as long as it sounds good.
 
Rodabod,

I must have been posting at the same time as you so I just read your last reply now. Maybe this is just a poorly made omni similar to what you can find in some cheap small membrane mics but then there'd be no need for a rear diaphram at all.

You keep refering to this as an M7 capsule but from the pictures this appears very different from an M7. It look more similar to a CK12 capsule but with a center contact point on the membrane.
 
[quote author="Tim Campbell"]
You keep refering to this as an M7 capsule but from the pictures this appears very different from an M7. It look more similar to a CK12 capsule but with a center contact point on the membrane.[/quote]

I read that this was an M7 at this website:

http://ds-audioservice.de/mikrofone-fotos/mikro2.html

If you scroll down until you find a "Reissmann" microphone you will see that it says, "Die eingebaute Kapsel ähnelt der M7, ist aber von schlechterer Qualität." ie. the capsule is a lower quality M7.

I'm assuming the author is correct - he seems to own and know a lot about microphones.
 
Doesn't look like an M7 - both Gefell and Neumann M7's have similar radial hole patterns, not a square pattern as shown in the photo. As for omni pattern - I've unintentionally made that when I got the drillings wrong on at least two or three of my capsules. But the back side always has less high frequency in it.
 
Clearly the BP hole pattern is not that of an M7. In addition, if there's only a single membrane it's definitely not an M7.
regards,
D.Bock
 
Thanks,

It is actually dual membrane / diaphragm, but I see what you mean about the hole arrangement.
 

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