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Old 07-20-2016, 01:31 PM   #1
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Lawrence Welk...

Greetings,
As part of a refurb of our 23' Penn Yan cruiser I am relocating the upper stereo speakers (hence the reference to Mr. L. Welk). Seems the way they were originally mounted was too close to the compass (I never noticed) and threw the readings off fairly substantially. Unfortunately, it is difficult to place them far enough away from the compass to negate magnetic effects. Is it possible to mount them close BUT equidistant from the compass so as to negate the effect of each individual speaker or am I relegated to a single set of speakers in the lower cabin?

I do NOT usually use the compass for navigation but I would still like it to be functional and somewhat accurate. Oh, and I DO have a place for the bubble machine...

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Old 07-20-2016, 01:56 PM   #2
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Lawrence Welk...

You may wanna vet this with someone more knowledgeable than I RT but am fairly sure high quality marine speakers are magnetically shielded so as not to affect compass.
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Old 07-20-2016, 03:26 PM   #3
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Don't the magnetic affects decrease with the square up of the distance? If so, I would think that it wouldn't take that much distance to negate the issues unless you have some very large speakers.
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Old 07-20-2016, 03:41 PM   #4
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Greetings,
Mr. CP. Not sure how "high quality" the speakers are but they do affect the compass reading within 3'-4'. I have no more space than that due to the minuscule fly bridge. It is a 23' boat after all...

My thought was to place the two speakers in such a fashion so the compass reading stays the same as without speaker placement. Sort of like the two metal compensating balls bracketing the compass on a steel vessel but I'm not sure that the speakers with their attendant magnetic fields would act in the same way.
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Old 07-20-2016, 05:17 PM   #5
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Yeah I'm not much help at all RT as I'm passing along some old information picked up many years ago and possibly misremembering. Hopefully either celectric or Northern Spy sees this thread because those two guys are loaded with resources for this esoteric kind of information. Good luck sir.
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Old 07-20-2016, 06:21 PM   #6
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why not place the speakers where you want them and buy some magnetic shielding material for the compass?
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Old 07-20-2016, 06:25 PM   #7
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For marine purposes, that be "Whelk"?
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Old 07-20-2016, 07:17 PM   #8
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Greetings,
Mr. JC. Hmmm...Shielding material. Might be the solution but would I not be better to shield the speakers rather than the compass? If the compass is shielded from magnetic influence it would cease to be a compass, would it not?

Whelk....

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Old 07-20-2016, 09:51 PM   #9
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Lawrence Welk...

You can buy shielding material. But I never have and have no experience with mu metal.

Theoretically, you have magnetic flux from the permanent magnet, and from the voice coil when energized. So be sure to test your placement while cranking out some music. The lovely Lennon Sisters may suffice. Oh that Peggy!

Prefabricated Shielded speakers have another permanent magnet (donut) to negate the lines of flux and a wrap of metal around them. At least the ones I've taken apart.

Can't you just swing ship and compensate your compass? Heck of a lot easier to do now with gps and keeping a heading going in the exact Cardinal directions.
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Old 07-21-2016, 07:59 AM   #10
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Try calling these folks, toll free. They are shielding material experts...LessEMF 1-888-537-7363

As for shielding speakers vs. compass, if the compass is shielded, any future electronic changes on your helm may already be covered if the compass has been shielded. I've seen ships shield compasses in box and tube style surrounds.
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Old 07-21-2016, 08:32 PM   #11
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The base of the compass should have a small magnet that can be rotated to adjust for local interference. Even the Ritchie on my 15' skiff is adjustable.
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Old 07-21-2016, 08:47 PM   #12
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I was going to call my new sailing dinghy "Bob," but not now, she is now formally "Lawrence Whelk" (assuming there is enough room for the name on her tiny transom).
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Old 07-21-2016, 08:57 PM   #13
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Quote:
Originally Posted by Xsbank View Post
I was going to call my new sailing dinghy "Bob," but not now, she is now formally "Lawrence Whelk" (assuming there is enough room for the name on her tiny transom).
Bob is a good name for a boat.

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Old 07-21-2016, 09:33 PM   #14
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Nobody said I was smart...I put an ac fan next to my magnaflux compass for my auto pilot...went in circles for 4days... I felt as if I was getting nowhere, so I went to all ahead full so I could get nowhere faster..... Duh....
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Old 07-24-2016, 10:02 AM   #15
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Fascinating and funny string.

Certainly, the compass has compensating magnets which can be adjusted for the installation. The problem here is that perhaps the speakers are not in use all the time and thus, also perhaps, the magnetic flux would vary. Shielded speakers are the way to go.

OTOH, your GPS display includes directional information. And your smartphone.
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Old 07-24-2016, 10:04 AM   #16
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Who knew? https://en.wikipedia.org/wiki/Whelk
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