PSN-L Email List Message
Subject: Re: Speaker Like Sensor ?
From: "Geoffrey" gmvoeth@...........
Date: Wed, 10 Mar 2010 19:28:21 -0700
This is kind of interesting
simply because I never heard
of such a thing before.
----- Original Message -----
From: "Keith Payea"
To:
Sent: Wednesday, March 10, 2010 9:43 AM
Subject: RE: Speaker Like Sensor ?
>I just saw an ad for this product the other day:
>
>
>
> http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-377
>
>
>
> It's sold as a way to turn surfaces into speakers. It has one of Geoff's
> requirements in that it has no cone.
>
>
>
> It's still an 8 ohm device. There's no spec on voice coil travel distance,
> and it will surely have the problem Chris mentions regarding small gaps
> which cause problems with arcing motion.
>
>
>
> Just another gadget to tinker with..
>
>
>
> Keith
>
>
>
> From: psn-l-request@.............. [mailto:psn-l-request@............... On
> Behalf Of ChrisAtUpw@.......
> Sent: Wednesday, March 10, 2010 4:15 AM
> To: psn-l@..............
> Subject: Re: Speaker Like Sensor ?
>
>
>
> In a message dated 10/03/2010, gmvoeth@........... writes:
>
> Hello instrument folks,
>
> Is it possible to get a speaker company to build the mechanism like a
> speaker without a cone that would be like 500 to 10K OHMS or more instead of
> the typical 8 ohms ?
>
> I think it may be the best of all sensors for a velocity type anything
> geophone ?
>
> Comments ?
>
> Hi Geoff,
>
>
>
> If you wanted 10,000 off, maybe.
>
>
>
> Speakers mostly use ferrite magnets which are weak and temperature
> sensitive. The coils are designed with tiny clearances to suit an in/out
> motion and don't work too well with coils moving in the arc of a circle. You
> can get small speakers with 1000 ohm coils.
>
>
>
> You definitely DON'T want coils much above 500 Ohms, or the resistance
> noise will be more than the background signal. Resistor noise is broad band.
>
>
>
>
> Using quad NdFeB magnets on mild steel backing plates and flat
> rectangular coils is the easiest construction for amateurs. See
> http://jclahr.com/science/psn/chapman/lehman/index.html for a coil + magnet
> drawing.
>
>
>
> Regards,
>
>
>
> Chris Chapman
>
>
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