Many thanks for the tip Kieth.

Larry

----- Original Message -----
From: "kpayea" 
To: 
Cc: 
Sent: Friday, January 30, 2004 11:44 AM
Subject: Re: Anther STM-8 question


> The one clue we can get from STM's web page is buried in one of the
> documents:
>
> "...3. The feedback transducer (which was the moving coil velocity sensor
of
> the basic seismometer) has a low DC resistance but a very high force
> constant (Newtons/Ampere), of the order of 10x the mass (in kg). ..."
>
> I think that in one of his e-mails, Sean-Thomas mentioned a simple way to
> measure this with your candidate speaker.  It went something like this:
>
> 1.  Set the speaker on the bench with the magnet down.
> 2.  Measure the position of the center dome.
> 3.  Set a known mass on the center dome.
> 4.  Put a current into the voice coil, and record how much current it
takes
> to return the center dome
> of the speaker to it's original position.
>
> I think I used a 9V battery in series with a 10K pot, a meter, and the
voice
> coil.
>
> Since you just need to return the cone to it's original position, no
> expensive measurement tools are needed.  Just rig up some kind of pointer.
> The only important things are a known mass and a decent ammeter.
>
> His original speaker was an 8" woofer from Radio Shack.  I'm sure it was
not
> particularly hefty.  A modern 6" woofer would probably have a higher force
> constant.
>
> Good Luck,
>
>         Keith
>
> Keith Payea
> Bryant Labs
> kpayea@..............
> www.bryantlabs.net
> (707) 566-8935
> ----- Original Message -----
> From: "Larry Conklin" 
> To: "PSN List" 
> Sent: Friday, January 30, 2004 8:12 AM
> Subject: Anther STM-8 question
>
>
> I am starting to collect materials for a vertical seismo based on the
STM-8
> design.  I have a rather small (7") speaker that I am considering for
using
> for the magnet and feedback coil, but I'm wondering if the magnet is
strong
> enough.  Can anybody give me some insight into how big a magnet is needed
or
> whether I would have to make adjustments elsewhere in the design to
> compensate for a smaller magnet?
>
> Larry Conklin
> Liverpool, NY
> lconklin@............
>
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)