Those electret microphone capsules are quite good but omnidirectional.
Is there any way to modify them to give a different pattern?
Modify the case, or some suitable shaped enclosure?

There are some digital recorders available with what looks,
though I haven't looked too closely, like two electret capsules
at right angles. If they are omnidirectional, they wouldn't give
much stereo effect. Anyone know what they are?

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Eiron.