New Speakers - Old Compass - Different Readings


Mark Erdos
 

Okay, this is stupid of me so, please hold off on the "what were you thinking" comments. We are all entitled to a little bit of stupid once and a while...

The outside speakers in the cockpit were shot. I purchased a replacement pair based on size and square shape. I think the original speakers were custom built for Amel made by Audax and housed in the plastic casing (does not act as magnetic shield) . I purchased a set of DC Gold N4C speakers. The magnets on the new speakers are much more powerful than the old speakers. I did not realize the DC Gold speakers would have much higher power magnets. I had sent an email to the manufacturer and they assured me they would not interfere with the compass if they had 3 feet of space. This turned out to be total load of codswallop. I can move the compass with the speakers when they are 6 feet away. When the speakers were briefly in the cut-outs my compass was off by about 90 degrees. I now think the new DC Gold N4C speakers are going to be a lesson hard learned.

I would still like to replace the speakers. I am now looking at PolyPlaner MA-4054 4” cone size two-way coaxial speakers. PolyPlaner claims "ultra-low magnetic field speakers eliminates the problem of speakers magnets affecting navigation equipment such as compasses and autopilots". I guess we'll see.

The instructions for the Plastimo Offshore Compass simply reads:
Deviation correction :
If deviation is no more than 7° : simply draw a deviation table assessing the error, and keep it for future reference.

If deviation is between 7 and 20° : we recommend that you have your compass compensated as a start, and then draw a deviation table. The compensation procedure is a delicate operation and should ideally be carried out by a professional compass adjuster.
I have a Raythenon fluxgate compass connected to the auto-pilot. I also have secondary electronic compass connected to my navigation software. I know the normal variance between my magnetic compass and the fluxgate. My question is: Once I install the new speakers, how do I adjust the helm magnetic compass to compensate for the change in the magnetic field surrounding the compass?

Thanks!

Mark

Cream Puff
SM2K #275

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