PSN-L Email List Message

Subject: RE: Speaker Like Sensor ?
From: "Keith Payea" kpayea@..............
Date: Wed, 10 Mar 2010 08:43:44 -0800


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












I just saw an ad for this product the other = day:

 

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=3D300-377

 

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….

 

         &nbs= p;      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://j= clahr.com/science/psn/chapman/lehman/index.html for a coil + magnet drawing.  

 

    Regards,

 

    Chris Chapman


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