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TUCoPS :: Hardware Hacks :: riflemic.txt

Rifle Microphone

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  %%        RIFLE MICROPHONE        %%
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  %%       Another file from:       %%
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  %%    Omnipotent, Incorporated    %%
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    This is a most unusual project; we
are going to mount a sensitive
microphone behind a series of acoustic
wave guides and hope for the best.
Actually, our wave guides are aluminum
tubes cut to resonate at frequencies
near the human voice range.  This
arrangement also serves to make the
unit highly directional as sound other
than that arriving at the mouth of the
tubes arrives at the mic in an
out-of-phase condition and cancels
itself out.

     With this easily constructed
device it is possible (under ideal
conditions) to pick up conversations
several HUNDRED feet away, in fact,
reports of recording conversations up
to 30 yards away THROUGH A CLOSED
WINDOW have been made...

     The device is quite easy to
construct:  First get together the
following materials:

[1]  56' of 3/8" outside diameter
     aluminum tubing (hardware stores)
[2]  1 sensitive amplifier with
     operating paraphenalia
[3]  1 sensitive microphone element -
     use either a good condenser or a
     crystal, as their outputs tend to
     be a bit higher than their dynamic
[4]  1 funnel
[5]  Assorted small hardware

     Cut the tubing into 37 pieces
ranging from 1" through 36" in one inch
divisions.  Now bundle them together
symmetrically with one end flush (as
shown).  As you assemble them, blue
them together in several places to
assure they remain in the state you
have put them in (were it only so easy
with people...).


         Flush ends of tubes

     Take the funnel and fit it around
the flush end of the tube bundle.
Being astute enough to read this, I am
sure you will notice the tubes do not
exactly fit into the funnel.  At this
realization, take a small hammer and
beatt the funnel to nearly as possible.
 Now fill the remaining spaces with a
good rubber based caulking compound.

     The microphone element is placed
in the neck of the funnel (with a
rubber grommet if it is small enough to
fit up into the neck - otherwise set it
into the other end of the neck before
caulking the tubing in place).  Glue
the mic into place and caulk any air
space around it.

     Run the microphone wires out the
neck of the funnel, glue in place, and
also caulk to give it a closed, fairly
air invincible seal around the entire
unti.  If you really feel up to it,
fiberglass resin can be used instead of
caulking compound.

   m    ###\
   i    ### \
   c    ###  \
        ###   \_________#  wire
   e    ###             #______
   l => ###    funnel   #
   e    ###    _________#
   m    ###   /         ^
   e    ###  /       grommet
   n    ### /
   t    ###/

     Run the output wires to your
amplifier and place the entire unit on
some sort of support, a camera tripod
being ideal.  (Need I remind you to
check matching impedances?).  The unit
should be aimed at the subject and then
panned about for maximum volume (sound
does not travel in a straight line, but
may vary with wind, etc).

     If wind noise overrides your
target noise you can place a piece of
cheesecloth across the end of the unit.
 If a particularly difficult noise
interferes with your pick-up you can
often plug up the tube(s) carrying this
noise with a cork.

      Good hunting, avoid paranoid
people who may feel your rifle mic more
than resembles the real thing...

     Coming soon from Omnipotent:

             THE BLITZ BOX!

     This will keep someone connected
to your phone line for as long as you
want.  It has endless applications.

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