Ruediger
    It may work as a strong motion sensor. I agree with Ted, usually you want
the natural period of the sensor to be longer than the lowest period you want
to record. Also since the output would be a function of the # of wire coils
turns you may have a very low output signal . Speakers usually have few turns.
What you describe maybe the begining of a force balance sensor but you would
need a displacement sensor included which would complicate matters. Do you have
access to magnet wire and simple rectangular magnets? You could use an electric
drill and wind your own coil of  1000+ turns on say a old spool like an empty
solder spool.  You could then put a rectangular magnet on both sides of the
coil. As Ted says you probable will have more interesting events if you do not
attach the groung to the end of the boom except as I have described above. I
hope this helps a little.  Most of us look around  to find possible sensor
parts from devices use for other things, for example computer harddrive driver
as sensor/coil pairs.
Barry


ted@.......... wrote:

> 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
>
> Please respond to PSN-L Mailing List 
>
> To:   PSN-L Mailing List 
> cc:
> 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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