When thinking about using loudspeakers for strong motion sensors, don't
overlook putting a negative impedance converter in parallel with the
speaker.  

It's a simple circuit with one op-amp and a few resistors that can make the
speaker into a closed-loop transducer with an acceleration output that can
be easily integrated to velocity.  Being closed loop, it can get around
many of the problems of the speaker suspension.

A few years ago a surplus store had parts from a force-balance weighing
scale.  It was very much like a loudspeaker but without the cone and used
flexures for the suspension.

It was only $5, but when I went back to get more, they were all gone.  If
anyone has a source of something like this, it could pretty easily make a
SM sensor.

Karl Cunningham
La Mesa, CA.
PSN station #40
karlc@.......

_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)