Convert omni electret into unidirectional

[jondoe]

Is there a way to achieve this ?
I've seen this schematic and said to myself:
I can understand the logic behind it but i know reality is a different beast so it may have a low degree of success.
Besides, i won't have time to test it until 2 weeks from now ...

I also thought of placing the condenser inside a bell or cone like structure at the closed end but backwards, with it's face facing the bell.
Basically i get a parabolic like receiver.

I have lots of condensers and they give me easily feedback but have excellent sound.
On the other hand i have some dynamics which are somewhat directional and don't give that much feedback but sound awful.

Any help is much appreciated.

[dnsey]

The trouble with the differential cct is that the diaphragms of each mic will be in a different physical plane, resulting in phase cancellation and reinforcement at different frequencies.
Is there a mechanical diagram that goes with the cct?

You could use a bell-like enclosure, but as with a horn, the lowst frequecy is determined by its diameter. To obtain a good f.r. you'd need a big bell!

Quite decent directional electret elements are available at only a little more cost than the omnis.

[jondoe]

As you can see the picture is not very telling but basically the capsules are tied together back2back at a distance just enough to not short.

Funny, i couldn't find any uni condensers around here ...
Maybe in england.

I don't care very much about the lower end. If it gets down to 200Hz i'm up high. I just need a sensitive device like a condenser is and for it to be directional let's say it's angle should be 45dg.

[dnsey]

The trouble with the differential cct is that the diaphragms of each mic will be in a different physical plane, resulting in phase cancellation and reinforcement at different frequencies.
Is there a mechanical diagram that goes with the cct?

You could use a bell-like enclosure, but as with a horn, the lowst frequecy is determined by its diameter. To obtain a good f.r. you'd need a big bell!

Quite decent directional electret elements are available at only a little more cost than the omnis.

[jondoe]

Am i seeing double or your posts are identical ?

[wxn]

Neat idea! About that plane and cancelation thing, I think one can get capsules closer side to side than back to back. Like this:
http://www.mp3forkidz.com/mic/mod.html

[dnsey]

Sorry abut the double post - ite didn't register first time so I re-submitted.

I agree that side-by-side would work better than back-to-back.

Electret capsules are so cheap that you might try experimenting with drilling a ring of holes in the rear of the body to convert an omni into a directional.

[Conrad Hoffman]

I have a fair number of these things, and have fooled with various mods people have published, like cutting the traces and adding a source resistor. No matter what I did, the combination of small diaphragm and internal FET still resulted in a mic with too much noise. For a measuring mic, they can work well because you can deal with the noise and they're quite flat. For a recording mic, I'm not so impressed. Better to invest the $57 or whatever, for a cheap studio type condenser with a large gold sputtered diaphragm. You'll have to build a phantom supply and maybe a preamp. Once you hear that, the little cartridges lose much of their appeal, though the big mics are far from flat.

[FastEddy]

" .. I agree that side-by-side would work better than back to back ..."

Dual element mics, side by side or top to bottom: This is similar to those funny looking microphones used by the Greatful Dead during the late eighty's and ninty's ... the principle being to cross cancel the background noise, yet let the musician's voice come through on top. The mics are each feed into seperate op-amp pre-amps, one inverting op-amp, one not ... then mixed into the line output driving XLR mic cables to the main mix down console ... worked pretty well (if you can stand the Dead's medeoker to bad vocals ...) I set up a similar dual combo mic for Mimi Farina once, one hot, but distant, one not, but in her face ... she liked it fine until she grabbed the weak link mic and pulled away from the hot mic = a frantic search at the mix console to crank up the mobile mic and reduce gain on he "hot" one.

early prototype: http://i.realone.com/assets/rn/img/5...648-slarge.jpg

[jondoe]

wxn:
One of the capsule has to be cardioid and i have only omnis. If i could get my hands on any cardioids i wouldn't be here.

dnsey:
i've read that the backholes are rather well calculated and executed in the number an diameter. I'll experiment when i have time.

Conrad Hoffman:
The intended use is for live sound, well, kinda (basically indoors with some speakers outside but only ocasionally).
But absolutely no for recording.
57$ you say, i only got around this one for that amount so ...
And i need about 4 of them in the worst case and better would be 8 so you feel my pain.
I am very satisfied with the sound these tiny capsules provide. I also have some dynamic but these tend to sound like a tin can ...
And i allready am in the mid of building preamps/mixer/phantom power

FastEddy:
Nice. But my mikes will be placed downfiring in a fixed position at 0.5m to1m above the speaker(s)/singers(s).

Somebody suggested i build a mike array. Say for each place where sound needs to be captured i place let's say 8 or more of these capsules in a spatial pattern that covers the possible movement of the person (which is quite small, let's say 5m/3m) and all of them turned down in volume so they add up in the mixer.

I shall see what i can do about them holes