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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