Magnet proximity and faceplate shaping

[kyrie48]

Hello everyone!
Hopefully someone has experience with shaping their own faceplates for custom fits. I've done one set of tweeters, and am planning on doing several other drivers--tweeters and dome mids. My question is: what results have you experienced regarding interference from one magnet to another, etc?
FYI, I use a Black & Decker 'Wizzard' for shaping--using a sanding drum.

Thanks, TTYL

[noodle_snacks]

I don't believe having magnets from speakers in close proximity would effect each other a noticeable amount.

[Shaun]

kyrie48

I don't know the answer to the magnet question, but I hope that noodle_snacks is right, as I'm doing exactly the same as you!

I'm using the RS 28 tweeter and RS D52 mid dome. I've decided that it is best to make the combo face plate in a figure of 8, as this allows one to still use a circle jig to make the cutouts. I'll probably get these professionally made if it doesn't cost too much.

[Willitwork]

For added peace of mind in this situation, one could simply use shielded units.

[Larry Lomax]

Hello,
By my experience, yes, the flux leeking from the magnet of a loudspeaker influences other loudspeaker nearby. Off course they do. But you don't have to mind about. The influence is so low you'll need good instruments to find out.
Speakers magnets are made to be a nearly closed magnetic circuit excep for the gap where the moving coil moves... So, the flux leaking from outside of the magnetic circuit is only a very little bit of the total.
Another point of view is that magnetic flux from magnets is static, this means no noise nor variation of anything nearby.
An extra point of view, in a speaker, in the middle of the gap in between the two expansion poles, where moving coil moves, there is a very strong magnetic flux flowing and a very strong magnetic field, nothing to share with the very little, small, amount of gouss lost from the outside of other nearby loudspeaker magnets.
Though those disperded magnetic fluxes can chasm your TV screen, or scope's screen, or even collect magnetic dust and iron chips.
Cheers

[Salas]

Traditionally loudspeaker engineers strive to get mids and tweeters together as close as possible for better lobes. They mount coaxial drivers on the back of strong professional woofers like Eminence Beta CX, Tannoy coax etc.
If there was a serious issue with magnets in close proximity, they would have mentioned strongly through the years in papers etc, and we would have seen shielding always and everywhere right from the first 2 way loudspeaker. So no issue apparently.

[AndrewT]

Hi,
slightly off topic but related.

Why is the backplate on a ferrite magnet smaller than the face of the magnet?

Would the flux going around the magnetic circuit have an easier job if the whole magnet face had a backplate to transfer the magnetic field to the pole piece?

[kyrie48]

Thanks for all the replies, now I have "peace of mind" with respect to future projects... don't have to worry about defeating my efforts by causing more problems than solving!
(Of all I've read about design, I never came across any mention of this concern... but there are several similars, as you all know)

Thanks one and all!!
TTYL

[Larry Lomax]

Originally posted by AndrewT
Hi,
slightly off topic but related.

Why is the backplate on a ferrite magnet smaller than the face of the magnet?

Would the flux going around the magnetic circuit have an easier job if the whole magnet face had a backplate to transfer the magnetic field to the pole piece?

Well, this is a good question...
I've seen this in many loudspeakers, as I've seen full backplates on many others...

I'd like to know too...

[AndrewT]

It cannot be to save weight and cost.
They are penny pinchers but there must be a technical reason.