True figure 8 with 2 electret capsules?

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True figure 8 with 2 electret capsules?

Postby Chinagraf » Fri Jan 08, 2016 6:27 pm

Anyone know ho to achieve this? I have some cardioid electret capsules and want to put a pair back to back and reverse the phase of the rear to make a true figure 8 pattern, but the capsules only have a ground and a +ve. If it was something like a ribbon I could use an output transformer on each, but I'm trying to make something small enough to mount on a dslr camera shoe to get like a Blumlein pair, and be powered by the camera. Any ideas out there?
Thanks.
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Re: True figure 8 with 2 electret capsules?

Postby rob » Sun Jan 10, 2016 8:31 am

treat them as two mics and mix them later to get fig 8
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Re: True figure 8 with 2 electret capsules?

Postby Chinagraf » Sun Jan 10, 2016 9:03 am

Hi Rob,
only got 2 tracks on the camera, so need to do it on the way in.
Might not be possible I guess without some sort of electronic balancing
and phase reversal in a little external box.
Thanks.
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Re: True figure 8 with 2 electret capsules?

Postby chrisp » Mon Jan 11, 2016 10:39 pm

Depending on the volts available, perhaps an unity gain inverting opamp would do the trick for you. If you get a dual opamp DIP8 single supply package (eg LM358 which can run on just 3V up to 32V) you could even put the other channel through a non-inverting opamp as well to buffer both electets. I'm thinking 4 resistors, a couple of MKT 100n caps to smooth the power at the opamp Vcc and Vee pins, Bob's yer uncle.

No comment as to whether this is a good idea or not, it's just a way to do what you want to do.
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Re: True figure 8 with 2 electret capsules?

Postby Chinagraf » Tue Jan 12, 2016 8:30 am

Thanks Chris.
Something along those lines is probably the only way to get the back capsule inverted.
Hoping to keep it small.
I guess the zooms can mount on a camera shoe so electronics in a small box with
capsules on top could be possibility. Oh well.
Cheers,

Andy
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Re: True figure 8 with 2 electret capsules?

Postby stosostu » Tue Jan 12, 2016 11:51 am

You might be able to pick up and old flash unit, Cashies etc, that will mount on the shoe and provide an enclosure for the electronics.
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Re: True figure 8 with 2 electret capsules?

Postby Chinagraf » Tue Jan 12, 2016 7:11 pm

Good idea Bob.
Thanks.
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Re: True figure 8 with 2 electret capsules?

Postby chrisp » Wed Jan 13, 2016 8:06 am

I second the Bob idea for an enclosure, and you could veroboard it along these lines - it would be quite small

Electet Fig8.png
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Re: True figure 8 with 2 electret capsules?

Postby Chinagraf » Wed Jan 13, 2016 8:15 am

Thanks Chris!
Cheers.
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