Repairing and modifying speakers

[Hayden]

I have lots of old/new broken speakers from 1” tweeters to 15” subs I wanted to fix/modify them,
1. Does anyone know how to dissolve the glue from the spider?
2. I need to get the magnet off, I tried tap with a hammer trick it didn’t work. I tried Prizing it with a screwdriver and hammer I gave up after I bent the screwdriver it didn’t work.

If anyone has any suggestion I would be grateful.

[K-amps]

Acetone or nail polish remover will open up many glues used in speaker...

[Cal Weldon]

Hayden,

After you remove the gasket and then the surround, cone, VC and spider unit from the basket you will find how the magnet is fastened. Sometimes you can unscrew it but often it will be be rivited and or glued and you have to knock off the ends of the rivets with a cold chisel or grinder or drill them out. If you've come this far, I hope you aren't trying to reuse the driver because it's now basically a large fridge magnet.

Also great for finding lost metal things in the pile of sawdust .

Cal

[hunter audio]

hi

Though long please read as this will let you open up all the parts of your drivers _

any acetate will work off the adhesive speacially benzoyl acetate , it is sometimes better than amyl acetate

to dis assemble the motor structure :-

at first you need to demagnatise the magnet - this is done by :_

on an impulse charger you will have to charge the motor structure / then charge it by reversing the polarity , if your charger does not have a polarity reversal swithch - you will have to pull out the motor structure and insert it the other way round in your charger

one needs to do this 4 to 5 times charging every time with a smaller current , and then reversing the polarity and charging with a even smaller current setting

once the magnet is considerably weak ( I have modified alnico , neodynium and ceramic - never got to discharge them completely )

on the threading of the top - plate ( the threading where the top plate is screwed on to the chassis ) insert a correct matching - threadsize - High Speed - Tempered Allen bolt - Keep screwing this with the key

With the torque the top plate will come off - for the 15 inch subs insert 2 allens and tigten both at the same time - you may need a friend to help you when you finally apply pressure to both the allens together

once the top plate is off have your friend hold the magent outer periphery strongly - take a soft hammer ( if you intend using a steel hammer soften the blow with wood or thick cloth ) hammer the pole piece evenly ( that is one good flat shot with a uniform force along the plane of the hammer head ) the bottom plate will come off - the hammer stroke need not be very forceful it needs to be smooth thats all - like a golf swing or so

another way of removing the bottom plate is to heat it - but if its a large magnet not well pressed while magnet manufacture it may crack

after you have got all the parts off all you need to do is some cleaning and then you can modify the motor structure to SFG insert shorting rings improve cooling - and really do a lot to effect the drivers performance - all you need is a good lathe machinist

we modify jbl 2226 as it has a few faults as they have retained the same chassis used in their earlier model and have inserted a spacer between the top plate and chassis

We modify the cooling of jbl 2226 and jbl 2242 where we change the entire pole piece - on a performance test between an original and modified ours takes 24bd low pass below 200 hz of a 1200 w QSC Powerlite and also 1200 w from a Crest

We modify a lot of Peaveys , Compressions etc too

all by the above process of opening up all the parts -
though one has to be very very dexter with the cones and dust cap to be able to re- use them again , you can apply a little bit of heat from a hot air gun to help you with the cone - spider bonding too

jbl 2226 - 15 inch 600 w pro , jbl 2242 ,18 inch 800 w pro

best of luck - have fun and hope you get good results

Suranjan Das Gupta

Transducer Design Engineer

[hunter audio]

hi

forgot to mention if you do not discharge the motor structure it is very diffcult to work with the pole plates when the magnet is magnetised , to me it is almost impossible to set it back maintaining an even magnetic gap

Suranjan

[K-amps]

You know your stuff Suranjan!

[Hayden]

If I demagnetize the magnet is it stuffed? Can I use it again?
How much heat can I apply to the magnet before it starts to weaken?
Thanks guys I’ll let you know how I go.

[cfb]

Two manufacturers of industrial adhesives for the bonding of ferrite to steel are PERMABOND and Dymax.

PERMABOND 581 and 681 magnet adhesives, both non-corrosive, the 681 is a two part adhesive and the 581 is the no mix surface activated type. From Dymax the 800 series of adhesives, their 842 adhesive is for magnet to pole bonding. You better be careful, these adhesives have about a 15 second set time, best to construct a jig to align the motor structure prior to attempting the bonding procedure.

Contact info at PERMABOND’s site, http://www.permabond.com/

and for the Dymax products, http://www.dymax.com/products/genera...bly/magnet.asp

hope this is helpful.

[hunter audio]

hi

hayden you cannot to discharge the mags by heating them - though they weaken while hot - they will not discharge effectivly enough for you to be able to work on them

the magnets when discharged are not stuffed

explanation :- any material will be magnetised if their molecular structure is aligned - with the - in lay man terms - + ve chrged ions facing one way and the -ve charged the other way

when a magnet is de magnetised the molecular structure gets aligned very haphazardly most =ve charges cancelling the - ve charges - where the effective force is weakened and a force field does not devolop effectivly

when you have modified the pole plates and set back the motor structure - and charge the magnet in a certain direction with - full current - to your chargers coils - the molecular structure of the magnet will get aligned again just as it was

there will be no drop of field strength if a magnet is demagnetised and magnetised again - provided it is done with a good charging field strength

analougously :-

we all are aware of cranes lifting - scrap steel from ships - they use a elctro magnet to lift the steel - place them on trucks

as a safety devise regulations require that if there is a power failure - the ton of steel should not come crashing down

what is actually done in advanced magnetic chucks is -
neodynium magnets are charged at the lift - and discharged when the load is to be delivered - that way the chuck is not power supply dependant and - safe

take care

Suranjan

[Hayden]

Finally I got it off with a blowtorch, it damaged the magnet a bit but it was because it was the one that I bent the screwdriver bashing it.
The trick is to heat the center of the back plat in tell you just start to smell the glue and leaver it off with a very sharp screwdriver or old chisel, surprisingly the magnet is not hot but warm and its still quite strong, I don’t know how much damage it did to the magnetic field so I will experiment with others I have.

Thanks you’ve been great