Low or non-magnetic marine speakers?

[Misil2]

I have another thread about problems with magnetic fields (speakers) and my autopilot "Raymarine st2000 +.

Raymarin ST2000 and deviation

One solution to this problem is to replace the speakers. I have found two possible solutions.

1. Osculati. They are claimed to be non-magnetic. They seem to use Ferrite magnets so it's a truth with modification?

Pair of Waterproof Non-Magnetic Speakers - White | Float Your Boat

2. Poly-planner that has "ultra-low magnetistic" speakers.

MA4056 - 6" 2 Way Coax Integral Grill Performance Speaker - Polyplanar LLC.

Do anyone have experience with these or have any opinions on whether it can work if the distance between the speaker and the autopilot is about 50 centimeters?

 

[oldmanofthehills]

A normal speaker depends on iteraction of coil with a magnet. A weaker magnet means a less efficient speaker and one can only go so far with careful magnetic circuit design. Ferrite magnets are fairly normal as powerful for their size and corrosion resistant so ideal for small speaker on boat.

Unless you go for capacitative speakers which are big and very expensive thats how it is. Of course you may not need great efficiency in a small enclosed area and the two you suggest may do you fine.

I wish I could separate my equipment by 500m as my radio interferes with my compass if I place both where I can see them. However your auto pilot does not need to know true magnetic bearing only relative so I am slightly surprised you have an issue and hadnt heard of that before. Good luck

 

[TernVI]

Speakers vary hugely in how much stray magnetic field they have.
The field should ideally be contained where it's useful, in the gap where the cone coil moves.

 

[BlueHeaven]

Speakers with a low external field used to be available. I used them on panels in TV studios where normal speakers interfered with the CRT monitors that were in use at the time. They employed a square cup shaped soft iron shield fitted over the back of the magnet. Vert effective. Whether they can still be obtained I don't know. Mostly I think they were elliptical speakers either 5x3 or 7x4 (inches) . Hope this helps.

 

[oldmanofthehills]

Speakers vary hugely in how much stray magnetic field they have.
The field should ideally be contained where it's useful, in the gap where the cone coil moves.

Indeed, and that is how any good speaker design should be. It may be that cheap car speakers are poor design as their requirement is limited volume and limited quality of sound, so they may not need such good design. However to reduce magnet costs any manufacturer will optimise the gap to some extent.

Perhaps solution is simply reasonable quality speakers.

What I was pointing out was the flannel in the adverts. Ferrite is the normal material - a bit like stating in advert the your car is made of steel