Ruediger,

You have certainly come to the right list!  And bravo, it sounds like you
are trying something new and exciting under difficult conditions.

If I understand your proposal correctly, you want to attach a solid plastic
stick to the end of the boom, perpendicular to the boom (making a kind of
"T" shape).  Then you want to physically attach the ends of the "T" to two
speaker cones, one on either side.  Movement of the boom would then move
the speaker cones and the attached coil, generating voltage.

I don't think this will work.  The boom must swing freely through the air.
Attaching the boom to the speaker membrane will keep it from moving at all.
You will have to separate the speaker coil and the speaker magnet from each
other so the boom can swing freely.  Then the relative motion of the
coil(s) and magnet(s) will generate the signal you are looking for.  This
procedure has been discussed many times on this list.

I don't think there is any problem having a coil/magnet assembly on either
side of the boom - many professional designs are built this way.  Don't
forget to wire the coils in such a way that the generated voltages are in
series and add rather than subtract from each other.

Now we'll let the real experts at you!  :-)

Ted Blank



Ruediger Wisskirchen  on 12/27/99 05:23:00 AM

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Subject:  Seismographs for students



High,
I hope that this is the right list for my question.
teaching in a highschool in Istanbul I had after the events from the
last months the idea, to build a seismograph with some students.
we studied the pages from Lary Cochrane from the Redwood City Seismic
Network, were we found some very good ideas and information.
My question: We found a lehman-Pendulum suitable for us. But as we have
hardly any tools we must search for ways to simplify everything. Is it
reasonable, to use mediumsize loudspeakers as sensors, where we want to
cut off only the black membrane but leave the coil attached to the
magnet by the brown  folded tissue-membran in order to keep it well
adjusted. Then we want to fix two of those speakers to the ground at the
left and the right of the end of the boom, so that a plastikstick glued
perpendicular at the end of the boom is squeezed between the two
speakers and induces a current in both of the coils when it moves to the
left and the right.. For those of you who have experience: do you think,
that this might work or is there no way to be sensitiv enough. And if
so, how should the amplifier and filter  look like for the two coils?

Thanks for any help

ruediger wisskirchen
rwisskirchen@.......



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