=C2=A0
i have been building paralleled arrays of capsules since 1985, initially
because the cheap capsules i could get in india were just too noisy to be u=
sed
singly. i then figured that if i mounted them in an array on a sheet of pla=
stic,
even just ten cm square, i would get an extremely directional mic which i u=
sed
for many documentary films.
initially i powered them with a 9 volt battery and single 2k2 load resistor=
-
shared by all the capsules. the sensitivity of individual capsules was lowe=
r
than if the circuit powered a single capsule, but the overall sensitivity -=
with
five capsules arranged in an irregular cross - was much higher.
Later i tried a current source - fet with a source resistor, as load, and i=
observed sensitivity change quite dramatically as the battery voltage fell =
which
was the opposite of what i expected. but i could run the battery down to
nothing.
these days i am running most of my microphones with the pip (2 volts) avail=
able
on the zoom h2, both with external fets (2sk 170) and built in ones. i am
getting very high output with a 25 mm electret capsule, and=C2=A0 lower out=
puts from
12 mm and 14 mm capsules.
there is an interesting design for upgrading a pip circuit so it gets to be=
really low impedance - useful for running long=C2=A0 cables. i can dig it o=
ut if
there is any intest. (it is there in the mic builders member's files)
umashankar
i have published my poems. you can read (or buy) at
http://stores.lulu.com/umashankar
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