corroding voice coils

[pdan]

Today I had a very interesting conversation with Lowthers. One question I asked was:What is the difference between silver voice coils and aluminium ones? They said that the silver coils give a smoother response than the aluminium coils, but that the aluminium coils have more "attack". This difference I put down to the fact that silver, being heavier than aluminium, would be more sluggish than aluminium.

Their second point though, really did give me something to think about: They said that aluminium coils need to be in regular use, otherwise they corrode.

Is there anything to this? I really don't think that Lowther is pushing silver coils, because the price difference is not that great.
Does anyone have any experience of aluminium voice coils corroding in drivers that have been idle for a sometime?


Cilla

[Cal Weldon]

Hi Cilla,

Interesting. I wonder if they were referring to the bobbins? The reason I'm asking is that the coil wire, as you know, is coated and has very little ability to corrode.

Mind you, I've not heard of a silver bobbin so who knows what they were referring to. Doesn't make a lot of sense to me.

I'm wondering if we should change the title of the thread to corroding instead of corrosive? Wat u tink?

[pdan]

Hi Cal,

I assume Lowther are referring to the voice coil windings--- can't think what else? Perhaps their own aluminium coils are uncoated, something to do with their "Hi-Ferric" thing?

Yes, please do change the thread heading.


Cilla

[Cal Weldon]

Done.

An uncoated coil? Isn't that a short?

[pdan]

Cal,

Thanks.

Think my brian is un-coated.......a Friday-night-special.


Cilla

[richie00boy]

Aluminium formers are used, but you'd never have a silver one. And as Cal says the wire must be coated (enamelled usually) or else it's just one big short circuit.

[Jon Ver Halen]

Hello Cilla:

In the decade that I have been involved with Lowthers I have never seen a corroded voice coil. They are built from enameled wire, and then have a varnish coating over them.

Once a customer complained that his voice coils were corroded, but that turned out to be nothing but the Hi-Ferric coating applied to them.

[pdan]

Hello Jon,

Is the ferric compound applied to aluminium voice coil prior to any coating? If so, would an electro-chemical reaction take place between the ferrous oxides and aluminium if, as is likely, oxygen is trapped - creating aluminium oxide?

I'm mystified by Lowthers comment; they don't seem to have anything to gain by it.


Cilla

[Jon Ver Halen]

Hi Cilla:

Based on second hand information, this is my understanding of how it works.

Wire comes in enameled, and they wind it into the voice coil. It is then attached to the voice coil with varnish. Hi-Ferric material is then brushed by hand onto the voice coil. The voice coil is then baked to make sure the Hi-Ferric is cured properly and will adhere to the the voice coil.

Not sure how any moisture could withstand the baking process, and if it did how it would penetrate the varnish and the enamel. Basically, I would not worry about this happening.

That being said, I like the sound of the silver better.

[pdan]

Hello Jon,

I'm sure you're right.

I'll give Lowther a ring and ask for more info on why they believe that drivers with aluminium coils are prone to corrosion if left unused for sometime.



Cilla