PSN-L Email List Message
Subject: Re: Speaker Like Sensor ?
From: ChrisAtUpw@.......
Date: Wed, 10 Mar 2010 07:14:31 EST
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_
(http://jclahr.com/science/psn/chapman/lehman/index.html) for a coil + magnet drawing.
Regards,
Chris Chapman
In a message dated 10/03/2010, gmvoeth@........... writes:
Hello=20
instrument folks,
Is it possible to get a speaker company to buil=
d the=20
mechanism like a speaker without a cone that would be like 500 to 10K OH=
MS or=20
more instead of the typical 8 ohms ?
I think it may be the best=
of all=20
sensors for a velocity type anything geophone ?
Comments=20
?
Hi Geoff,
If you wanted 10,000 off, maybe.
Speakers mostly use ferrite magnets which are=
weak=20
and temperature sensitive. The coils are designed with tiny clearances to=
suit=20
an in/out motion and don't work too well with coils moving in the arc of=
a=20
circle. You can get small speakers with 1000 ohm coils.
You definitely DON'T want coils much above 50=
0=20
Ohms, or the resistance noise will be more than the background signal. Res=
istor=20
noise is broad band.
Regards,
Chris Chapman
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