Make directional mic

[PeteMcK]

I'm thinking it can't be too hard to make a directional mic out of a couple of electret elements, but can't find much info at all on the web. (I don't want a shotgun mic, just a normal directional mic for recording)
How about connecting a couple of electrets back to back and mixing the outputs out of phase, with perhaps a level control on the rear element - would that work?

I suppose the alternative is to mount an element in a pipe and cut slots behind it to get a cancelling wave from the rear - then I'd have to figure out the placement & size (or guesstimate them from an existing mic?)...

[TheSeekerr]

Or you could just buy a cardioid/hypercardioid electret capsule.

I -think- that by using a hypercardioid capsule on the front and a cardioid capsule on the rear, and mixing the rear one out of phase, you should get a fairly directional mic.

I think there's a yahoo group called "micbuilders" or something very much like it, try asking over there.

[PeteMcK]

Hi Seekerr,
"cardioid/hypercardioid electret capsule" are these available in Aus? (I've only looked at Jaycar and Altronics, they only have cheap omni capsules)

[TheSeekerr]

Heh, quality electret inserts in Aus? I doubt it. I know they exist, though....be nice if somewhere like Farnell carried some good ones.

I've heard good things about Transsound Electrets , but shipping is the killer.

[PeteMcK]

pp37-38 in this give me hope:
http://www.neumann.com/download.php?...d=docu0002.PDF

[Steerpike]

You can make the omnis unidirectional by drilling tiny holes (0.8mm) in the phenolic/paxolin insulator board at the back. It lessens their bass response though which has to be corrected electronically.

[PeteMcK]

thanks Steerpike, cheap enough to try...

Found some unidirectional capsules in the Farnell catalogue, at 10x the price in the US! :-(

Parts express have a panasonic one available, might order some in the New Year...