JBL L15 woofer repair question

dabbler · 5th January 2011, 02:47 AM

The magnet has fallen off the basket on my 115H woofer. I imagine I can just glue it back on however I need to know how to centre the voice coil properly. How can I tell if there is a gap between the voice coil and the magnet and that they are not rubbing together?

vaughn · 5th January 2011, 02:51 AM

this is a pretty good tutorial that I followed;

Resetting a loose magnet (with pictures) - AudioKarma.org Home Audio Stereo Discussion Forums

dabbler · 5th January 2011, 02:58 AM

Quote:

Originally Posted by vaughn

this is a pretty good tutorial that I followed;

Resetting a loose magnet (with pictures) - AudioKarma.org Home Audio Stereo Discussion Forums

Thanks Vaughn,

Its alot trickier than I thought! I was hoping I didnt have to remove the dust cap or make special jigs.....such is life.

vaughn · 5th January 2011, 03:04 AM

Yes, a jig is mandatory unfortunately. There is so much lateral force pulling those magnets together and collapsing the gap (and clamping down on the voice coil) that you need something serious to keep it all in place.

Zero Cool · 5th January 2011, 03:11 AM

yup. I attempted this once. there was just no way to do it with the cone in the basket. I ended up carefully removing the cone which took me 4 days! but i got it and the spider out with minimal damage. then found a plastic cap that fit in the cap between the pole piece and the top plate and re-glued the ferrite magnet to the top plate. it worked. but i had a heck of a time getting that cap back out of the gap. again persistence wins several hours of picking at it and i got it out. was able to reglue the cone and spider back in place and it lasted for 4 years before falling victim to lightning strike/blown amp!

MarkLandin · 6th January 2011, 06:59 PM

Parts Express does driver repair, if you decide it's too much hassle to DIY.

speaker dave · 6th January 2011, 08:49 PM

I looked at the AudioKarma thread. Thats pretty hardcore! It is especially tough if the magnet structure has split as shown, because it will want to jerk sideways and will likely pinch and damage the voice coil. That is why he made the multibolt centering fixture.

I am assuming in your case the magnet structure fell off as a complete unit? Even so is the coil undamaged? You need to be careful not to fold over or otherwise damage the voice coil former.

If the magnet structure came off clean and the coil is good then you should try to put it back together. As AudioKarma shows I would take a sharp razor knife to the dustcap. Cut it close to the cone but be careful not to pierce the cone or cut through a voice coil wire. You will be able to glue it back on a barely visible joint.

Find some business cards or other suitable shim material that lets you center the coil in the magnet gap without any play (make sure you have the same number of cards on each side!). Glue the magnet back to the basket with a good two part epoxy and make sure it is fully cured before you proceed.

Good Luck

By the way, I designed the L15 around 1982. Cute little system.

dabbler · 24th January 2011, 05:50 AM

voice coil is undamaged - the magnet fell off during transit while it was laying face up in the box- so the crossover took a hit but i just need to re-glue the inductor back on. I might call up a speaker repairer to get a quote before I operate with my clumsy hands.

Quote:

By the way, I designed the L15 around 1982. Cute little system.

I feel privilaged to be in such esteemed company!

NAT.D.BERG · 15th September 2011, 11:42 PM

Probably too late now but I found a tip online to help me with a mis-aligned magnet, dropped out of place with age.

Basically it involved putting the magnet on a low heat on the stove (electric plate hob, not gas! ) until it got more than just warm, not 'hot' though. This softened the glue just enough that one could tap (more like 'hit') the magnet about just enough to free up the coil and cone. I tapped with a hammer and a block of wood (to prevent damage to the magnet).

Keep turning the driver over to check the freeness of the cone by hand and if it's binding or rubbing, work out where and tap in the right place to move the magnet again.

Probably took me an hour and a half (well it was the first time I'd done it and kept going too far or not hitting hard enough)

Worked a treat and then the whole thing cooled and (hopefully!) the glue set again.

So... in your position that would mean gluing the magnet on with a suitable glue as best you could and then performing the procedure above.

It meant that I didn't have to remove the dust cap on some vintage drivers that I'd never be able to replace properly.

Worth a try before taking it apart. Wish I'd done this before on another driver that's now sitting about 'cos I can't find a suitable dustcap..

5th January 2011, 02:47 AM	#1
dabbler Account disabled at member's request Join Date: Apr 2010 Location: Between cities!	JBL L15 woofer repair question The magnet has fallen off the basket on my 115H woofer. I imagine I can just glue it back on however I need to know how to centre the voice coil properly. How can I tell if there is a gap between the voice coil and the magnet and that they are not rubbing together?

5th January 2011, 03:11 AM	#5
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	yup. I attempted this once. there was just no way to do it with the cone in the basket. I ended up carefully removing the cone which took me 4 days! but i got it and the spider out with minimal damage. then found a plastic cap that fit in the cap between the pole piece and the top plate and re-glued the ferrite magnet to the top plate. it worked. but i had a heck of a time getting that cap back out of the gap. again persistence wins several hours of picking at it and i got it out. was able to reglue the cone and spider back in place and it lasted for 4 years before falling victim to lightning strike/blown amp! __________________ It's not about what you can BUY...It's about what you can BUILD!

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5th January 2011, 02:51 AM	#2
vaughn diyAudio Member Join Date: Feb 2008	this is a pretty good tutorial that I followed; Resetting a loose magnet (with pictures) - AudioKarma.org Home Audio Stereo Discussion Forums

5th January 2011, 03:04 AM	#4
vaughn diyAudio Member Join Date: Feb 2008	Yes, a jig is mandatory unfortunately. There is so much lateral force pulling those magnets together and collapsing the gap (and clamping down on the voice coil) that you need something serious to keep it all in place.

6th January 2011, 06:59 PM	#6
MarkLandin diyAudio Member Join Date: Dec 2010 Location: Tulsa, OK	Parts Express does driver repair, if you decide it's too much hassle to DIY.

6th January 2011, 08:49 PM	#7
speaker dave diyAudio Member Join Date: Nov 2009 Location: Toronto	I looked at the AudioKarma thread. Thats pretty hardcore! It is especially tough if the magnet structure has split as shown, because it will want to jerk sideways and will likely pinch and damage the voice coil. That is why he made the multibolt centering fixture. I am assuming in your case the magnet structure fell off as a complete unit? Even so is the coil undamaged? You need to be careful not to fold over or otherwise damage the voice coil former. If the magnet structure came off clean and the coil is good then you should try to put it back together. As AudioKarma shows I would take a sharp razor knife to the dustcap. Cut it close to the cone but be careful not to pierce the cone or cut through a voice coil wire. You will be able to glue it back on a barely visible joint. Find some business cards or other suitable shim material that lets you center the coil in the magnet gap without any play (make sure you have the same number of cards on each side!). Glue the magnet back to the basket with a good two part epoxy and make sure it is fully cured before you proceed. Good Luck By the way, I designed the L15 around 1982. Cute little system.

15th September 2011, 11:42 PM	#9
NAT.D.BERG diyAudio Member Join Date: Nov 2006	Probably too late now but I found a tip online to help me with a mis-aligned magnet, dropped out of place with age. Basically it involved putting the magnet on a low heat on the stove (electric plate hob, not gas! ) until it got more than just warm, not 'hot' though. This softened the glue just enough that one could tap (more like 'hit') the magnet about just enough to free up the coil and cone. I tapped with a hammer and a block of wood (to prevent damage to the magnet). Keep turning the driver over to check the freeness of the cone by hand and if it's binding or rubbing, work out where and tap in the right place to move the magnet again. Probably took me an hour and a half (well it was the first time I'd done it and kept going too far or not hitting hard enough) Worked a treat and then the whole thing cooled and (hopefully!) the glue set again. So... in your position that would mean gluing the magnet on with a suitable glue as best you could and then performing the procedure above. It meant that I didn't have to remove the dust cap on some vintage drivers that I'd never be able to replace properly. Worth a try before taking it apart. Wish I'd done this before on another driver that's now sitting about 'cos I can't find a suitable dustcap..

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