In a message dated 15/02/02, gbl@....... writes:

>     I did the same with a peizo with the same good result. You can slow it
> way down with a home brewed sine wave oscillator. I also put it under one of
> the balancing legs of a horiz seismo and was going to try it with STM's vrdt
> design.

Hi Barry,

       You can buy really strong chunks of PZT for use replacing gas 
igniters. They will take several pounds load, but you may need quite large 
driving voltages.
       I put a disk of thin rubber over a large loudspeaker, a circle of 1/2" 
polystyrene sheet on top and the geophone on top of that. The centre of the 
speaker had an airtight dome. If you also mount a small magnet on the sheet, 
you can sense the movement with either a coil or a linear Hall chip.

       Regards,

       Chris Chapman
In a message dated 15/02/02, gbl@....... writes:



  
;  I did the same with a peizo with the same good result. You can slow it

way down with a home brewed sine wave oscillator. I also put it under one of

the balancing legs of a horiz seismo and was going to try it with STM's vrdt

design.




Hi Barry,



       You can buy really strong chunks of PZT for use replacing gas igniters. They will take
 several pounds load, but you may need quite large driving voltages.

       I put a disk of thin rubber over a large loudspeaker, a circle of 1/2" polystyrene she
et on top and the geophone on top of that. The centre of the speaker had an airtight dome. If you also mount a small magnet on 
the sheet, you can sense the movement with either a coil or a linear Hall chip.



       Regards,



       Chris Chapman