An alternate way of varying mic patterns.

[jdbakker]

Hi all,

I've been looking at variable-pattern condenser microphones lately (like the G7). As you know, this is commonly achieved by varying the voltage on both diaphragms with respect to the backplate, with the backplate tied to the FET/tube of the mic's internal amp. When both diaphragms have the same voltage wrt the backplate the microphone will have an omni characteristic, opposite voltages wrt the backplate yields a figure-of-eight, and in-between polarizations give various other patterns.

I was wondering if it's possible to achieve the same effect by connecting the backplate to the usual +40...+80V capsule bias, attaching a separate FET/tube head to each of the diaphragms and weighed summing of the outputs. This way, adding the signal from the front diaphragm to that of the rear diaphragm should give an omni response, subtracting the signal from the rear dia from that of the front should produce a figure-of-eight and so on and so further. Right ? Naturally there will be some phase imperfections caused by component mismatches, but I don't expect those to be worse than the imperfections in the capsule/mic enclosure itself.

Could all of this work, or am I missing something big here ?

JDB.

 

[Gus]

Been done

From what I have read at Klaus's it SEEMS that the 149 has the front connected to a tube circuit and the back to a fet circuit and the patterns are done in the electronics. I don't know if this true but some of the posts seem to "add up" to this. I have not been inside a 149 to check this myself

There was a russian microphone I read about on the web that did the patterns in the electronics IIRC.

I think the samson C03 uses two cardiods and a CAD microphone model used two cardiods

The 7 series by David J.

I would guess there are more

 

[SSLtech]

Soundfield mic essentially does this, but with 4 capsules.

You can't get more flexible or more powerful than a soundfield... it also allows you to do MUCH more powerful things with M/S, and to filter the back capsule, to reject noisy bits of the spectrum for example.

Native B-format mics such as the Josephsen C-700S work in a similar -but not identical- fashion.

I've built a few mics that way, the only real complexity/penalty is that you have to be VERY careful with gain tracking/matching if you sum at line level... and summing at mic level can present rather more challenges as regards noise, etc.

Keith

 

[recnsci]

And you could record signals from separate diaphragms on separate
channels, so you could apply different processing to each.

cheerz
ypow

 

[BradAvenson]

I believe the Josephson 700 is an omni on top of a figure 8. By adding these two capsules together you can determine the pattern after you record both channels. Its a 2d version of the soundfield idea I suppose.

 

[SSLtech]

Right you are Brad, though I would say that the 700 is one-dimensional, since you can only alter the pattern along a single axis.

The 700S is the same as the 700 but with an assitional SIDE figure-8, so that you can alter along (and between) TWO axes, so that version is 2-dimensional, to my way of thinking...

The Soundfield of course adds a vertical axis, so you get front/back (a-la 700) PLUS left-right (a-la 700S) and vertical (a la nothing else on earth! :wink for some SERIOUS after-the-fact power!!!

People get scared of this stuff, but it's just M/S + vertical with the additional control of ALL the patterns... easy enough, really.

Keith