On Sat, 18 Mar 2006 03:49:57 GMT, "derbyrm"
wrote:

The lines of force follow the path of least reluctance, so you build a box
of iron (or Permalloy if you're rich) and they follow around it instead of
straying into the air beyond. (much oversimplified)

Thanks
Mark E. Williams

All the suggestions that occur off hand are of the nature of "You use this
end of the hammer." (Actually, that would work too.)

Roger

http://home.insightbb.com/~derbyrm
"Jim Conlin" wrote in message
...
My problem was that the speakers were moveable, as were the bracket
mounted
speakers referenced in the first post. If the orientation or location of
a
permament magnet speaker can be easily changed, What's the navigator to
do?


"derbyrm" wrote in message
news:rQUSf.829891$x96.477169@attbi_s72...
Swinging the vehicle to check the compass is a basic navigator duty. For
aircraft there's a compass rose on the tarmac, for boats/ships there are
hand bearing compasses and pelorus (pelori??), but see
http://www.boatsafe.com/nauticalknowhow/bearing.htm Check with all
equipment on board and energized and the engine running (if applicable).
A
deviation card should be mounted on the compass, or close by. Speaker
magnets are just one of many sources of deviation.

Then again, there are really cheap hiking-type GPS units that will tell
you
your track (but not your heading).

Roger

http://home.insightbb.com/~derbyrm

"Jim Conlin" wrote in message
. ..
I missed that day in fre\shman physics, so i remain not informed but
concerned.

A long time ago, i almost had a very nasty grounding because some
speakers
which had been brought on board deranged the compass.


"Maynard G. Krebbs" wrote in message
...
On Fri, 17 Mar 2006 14:44:53 GMT, chuck wrote:

Marine-type speakers are generally shielded (as are speakers intended
for use near CRTs) so this should not be a problem. The speaker
description/packaging should indicate whether it is magnetically
shielded.

I'd be interested in hearing of any cases where a magnetically
shielded
speaker has interfered with magnetic compass readings.

Chuck


Something I always wondered about is, "How do you magnetically shield
something."
Doesn't Magnetism pretty much go through things. How could you shield
a speaker's magnet so it wouldn't affect a compass?
Mark E. Williams