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 used
singly. i then figured that if i mounted them in an array on a sheet of
plastic,
even just ten cm square, i would get an extremely directional mic which i used
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 lower
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) available
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 lower outputs 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 cables. i can dig it out 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
|