Adding extra magnet

[jamikl]

What happens, if anything, when an extra magnet is added to the rear of a speaker. I know it has been mentioned in here somewhere but I can't find it. If it has any advantage is the magnet held in place by its own attracti0n or is it glued. Thanks for any reply.
jamikl

[Moondog55]

Piggyback magnets are aligned with both magnetic fields in same direction.
Bucking magnets have fields reversed, in both cases they are usually glued on.
bucking magnets are used for shielding purposes, piggyback magnets to alter T/S parameters, although bucking magnets also alter T/S parameters, opinions divided on the efficacy of doing so, I tried it once and could hear no difference so never tried it again, Sreten says it is a bad idea, others have used it but I can't find the old links.
A well designed speaker shouldn't need any extra magnets and bad / cheap designs are probably beyond help anyway.
BUT all speaker builders wind up with lots of spare magnets so why not try it and see if you can measure any difference????

[jamikl]

I have some Eminence Beta 15s and some ruined Pioneer 12" car subs which I picked up roadside. I am wondering whether adding the Pioneer magnets to the Eminence will make any difference.
jamikl

[Moondog55]

First off are the car subs worth rebuilding??

I wouldn't ruin a good cast frame just to scavenge a magnet.

Do you have any measuring equipment? as this isn't something I would imagine you can hear easily.

If it is just a magnet or two I can supply plenty of those, save throwing them in the bin when we move next month

[sumit]

" I have some Eminence Beta 15s and some ruined Pioneer 12" car subs which I picked up roadside. I am wondering whether adding the Pioneer magnets to the Eminence will make any difference "

Adding a magnet results in a decrease in qes.....u won't here any diff though..... the polarity should be same..that is while attaching the spare magnet u should feel that the speaker's magnet is repelling the other magnet and not attracting it. Otherwise qes might increase....

[Saturnus]

It's hard to generalize but all things being equal an extra magnet attached with opposite polarity will:

- increase sensivity slightly by bucking stray magnetic field back and thereby increasing force factor.

- lower Qts slightly by lowering Qes for the same reason as above.

- dramatically decrease stray magnetic fields, not as effeciently as a proper shielding but for most purposes this is the primary benefit.

Attaching a magnet with equal polarity will:

- increase sensitivity and decrease Qts for the same reasons as above but it will have more effect because you're adding extra magnetic field strength and not just focusing the already existing.

- dramatically increase stray magnetic fields which in itself can be a major drawback.

It should be noted that except for the increase/decrease in stray magnetic fields the benefits are minor to minute. And that the more well designed the drivers magnet motor system is in the first place the less benefit you will see.

[nickmckinney]

Only way to do it is to add in bucking style. This forces more of the outside stray flux back into the center increasing the Bl of the driver (putting more B in the usable gap). If the speaker has a steel basket and/or a motor with metal plates the same size or larger than the magnet then the effect will be greater since these usually have larger stray fields.

[sreten]

Originally posted by Moondog55
... Sreten says it is a bad idea ...

Hi,

Not sure what I said was a bad idea, piggyback perhaps ?
That basically can only make things worse ....
Bucking magnets do work it terms of bucking magnetic fields.

Neither way works very well in terms of efectively using the
additional magnet because its not placed in the magnetic
circuit, in other words buy a driver with a bigger magnet
in the first place.



The extra full size magnet (used bucking style) makes a 10%
difference, not very cost effective compared to enlarging the
"proper" magnet.

/sreten.

[nickmckinney]

The problem with ceramic is that you need to go wider to get more real strength and judging by that picture those are as wide as they can go. Going taller with ceramic even inside the motor doesn't get you anywhere near as much as wider.

[Moondog55]

Hi Sreten, yes it was "piggy-back" you said was a bad idea.