Taking off the magnet cover!

[panos29]

How can I take off the magnet cover from an 2220A driver? Is this doable at all? I have reasons to believe that the magnets have moved, is it possible?

[edgewound]

How can I take off the magnet cover from an 2220A driver? Is this doable at all? I have reasons to believe that the magnets have moved, is it possible?

No...the magnet is housed in a cast iron pot. The magnet is underneath the top-plate which would require cutting out the cone assembly, unbolting the frame from the magnet assy and then prying apart the top plate from the pot....which will substantially discharge the magnet, which then would require a gap re-align and magnet recharge.

It takes quite a huge force to move the magnet out of place on that driver. A force large enough to most likely break or bend the frame from impact....but to answer the question about a cover....no.

[panos29]

That is what I was afraid off. I got 2 speakers where one cone is heavily rubing and the other seems moved to one side like the voice coil is displaced about a quarter of an inch causing the cone to lift from one side and sink down to the other. Obviously the speakers are not at all repairable althought he cones seem in excellent condition as the chassis too. Any other possibility to straghten the chassis like they do to the bent rims of some cars?

[GordonW]

Before condemning the frame, be aware that I've seen recone kits (a few factory, but more frequently aftermarket) that were put together with the cone installed crooked onto the coil... which can lead to the "cocked" appearance (where one side of the cone is "higher" than the other) you describe. In many cases, the speaker will actually play nominally fine... without rubbing. However, in some cases, the stress caused by the crooked cone can cause the spider and/or surround to "creep", or the cone to warp, which may cause the speaker to start rubbing after time has passed... the cone assembly might work at first, but fail later due to nothing other than stresses due to the improper assembly.

One way to check for frame warpage would be to put the speaker face down on a flat, level surface. First, make sure that the flange isn't warped (ie, the flange sits flat against the surface ALL the way around). Next, use a bubble level on the back of the magnet... it should show level no matter what direction you rotate it on the back of the magnet of the 2220A. If the flange is straight and the magnet is level, chances are the frame isn't bent...

As for magnet shift... the only way to check that, is to rip out the cone kit, and use a feeler gauge all around, inside the gap. Should read within one or two thousandths variation, tops... otherwise, it's shifted and needs serious repair (probably factory only procedure)...

[panos29]

Dear Gordon,
Thanks for answering, the speakers are probably bent as the woofers with face down on the floor they do not touch the down all the way around the circumference there are 2 points with a distance of 3-5mm. Moreover I have strong reason to believe that the woofers were properly reconed with original cones, as these were bought from a member of this forum and were working well prior to shippment, this was done from droping of the box at the customs for sure as the packaging was inadequate to say the least. I would like to ask the way the magnet is held on the plate besides the obvious magnetic force, is there any glue present?

[subwoof]

I would check the frames "flatness" with the mounting foam removed so the metal is the high point all around the rim. Then find a REAL flat surface - the top of a high quality tablesaw or machinist's granite block are the best choices.

The magnet *assembly* is held on by 6 short 10-32 bolts that are under the spider ( no glue unless a reconer added it ). If you carefully remove the dustcap by cutting them out ( replaceable by any competent speaker tech ), any shift will become apparent.

In this situation I have removed the entire cone assembliy by using MEK on the surfaces that are glued ( spider rim and surround ) and then un soldering the lead wires.

This only works if the cone is somewhat new and the glue softens. It takes a lot of patience to get them out undamaged but if you do, the frame can be replaced.

One time I was able to unglue the spider and get a right angle phillips screwdriver on the 6 bolts. Those speakers became passive radiators..:)

In cases where there is this much damage, all the work is sometimes for naught when a bent voice coil or warped spider is found.

When I ship speakers, they are bolted to a sheet of 3/8 plywood with all 8 holes to prevent this from happening. Why some sellers think peanuts or bubblewrap is good enough is beyond me..

:cheers:

sub

[panos29]

In this situation I have removed the entire cone assembliy by using MEK on the surfaces that are glued ( spider rim and surround ) and then un soldering the lead wires. sub

May I ask what kind of solvent is MEK, maybe its chemical composition or commercial name or something(I am working in pharmaceutical company and got access to almost any chemical)!

[jbljfan]

Methyl Ethyl Ketone (2-Butanone)

http://www.epa.gov/ttn/atw/hlthef/methylet.html