JBL LE5-10 or LE5-12 midrange aluminum dome replacement - anyone done one?

mech986

mech986

Lunatic Member
I've got an LE5-12 with a pushed in aluminum center dome - looks like it would be difficult to pull out with any decent appearance or hemispherical form. There are replacement aluminum domes painted black on both sides available from Midwest Speaker so at least there's a viable option for repair.

http://www.ebay.com/itm/Aluminum-Du...140386?hash=item235a051ee2:g:VygAAOSwKIpWDDaZ

s-l500.jpg


LE5-12 typical appearance, the LE5-10 is exactly the same except with a black painted frame.

s-l1600.jpg




Has anyone done this repair and any tips on how to remove the original dome and replace it? Thanks for any discussion.
 
Register to hide this ad
mech986 said:
Thanks, your thread and pics were very helpful. The dome was stuck down pretty good?
Click to expand...

On the practice driver it didn't seem to be glued down too hard at all, but of course the good driver proved to be a little harder. I used a real heat gun, but I would probably recommend a hair dryer and patience. It's really about a ten minute repair tops.
 
After reading your comments, I've ordered a dome to try out on my smushed one. I'll let you know how it turns out.
 
tonyk's suggestions sounds like an approach to consider. I have done a few of these another way. I took an exact-o style pointed blade knife and cut away the dome down near the rim. Take care to use slow and deliberate cuts. Once a hole was established I used needle-nose pliers to support the dome as I cut. Then a small bead of glue around the old rim still attached to the cone. Using a piece of tape gently attached to the replacement dome- they will dimple all too easily- I guided the replacement right on to top of the old dome's rim. Some care has to be made in pressing down on the rim of the new dome as it will ripple if too much pressure is applied. Can't tell there is a new dome when done. This works provided this replacement dome is exactly the same as the old, of course.
 
If you have a well ventilated area, MEK will soften the glue. (It's the solvent that all the original JBL glues were dissolved in. Please be careful with MEK as it is highly flammable and softens a lot of plastics (and will soften your surrounds if you get it on them.
 
True, MEK would work but I'd be worried about softening the nearby voice coil / cone joint junction.
 
I cheated on this process with a pair of LE-5xx drivers that had wrinkled domes. I measured them to see frequency response before doing anything. Then I tried overlaying paper domes---this measured worse (not surprising), and the paper domes were removed before the Alene's tacky glue dried.

What did work well was to carefully cutout circles of black grill cloth and glue it on just around the edge/circumference with Alene's tacky glue so that only the dome was covered. The drivers look much better than with the dented domes showing, and measure just fine in the usable mid-range. The area above 5khzwas down a dB or two, but in my book that is fine for a mid-range. These were not part of a system, I got them as a pair to use in DIY endeavors.

The (dented) aluminum domes had extended, but uneven (wiggly looking) response into the over 10khzrange, which just seems like a problem to be dealt with, rather than a desirable feature, for a mid range driver. Maybe the combined response might help in a speaker with an LE20 paper cone tweeter to boost response over 10-12khz?

I have a nice pair of L166, with aluminum center-cap LE5xx mids, and dome tweets. It is hard for me to see how having the mids play above 10khz could help with anything----but I must say that the speakers are dynamic and enjoyable to listen to. I don't remember measuring them. The foams went bad, so I fixed those, but the other drivers, crossovers and grills are intact and original.
 
I have a question about a NON-WORKING pair of LE5-10(see last comment): WHY don't they work given THE FACTS:

1) Musical signal input results in no sound that I can hear.

2) Using a 1.5 V battery click tester, one of them makes a very slight sound with my ear pressed to it.

3) They each measure about 5.3ohms across the hookup terminals.

4) I can move the cones a couple of mm by pressing on them---and hear no scraping.

5) Aside from the dented domes, there are no visible signs of distress, no excessive corrosion, just a 45-or-so year-old patina.


Also interesting, but not related: The“10” on the back plate is marked by hand in red maker, not printed, and this likely was done decades ago, from what I know of the history of this pair. There is nothing printed on the back plate. The cone backs are stamped in white: 570771. There are 3 rivet heads(?) holding the the back plate on.
 
Talking to a friend about the LE-5 mids I mentioned above, all he could think of was that the (ferrite) magnets had no magnetism. So I checked it out---and, yep, ferrous metal objects, even small ones, don't stick!

Anyone seen such a thing?

Pretty sure it would cost more than these are worth to have them re-gaussed.
 
howgee said:
Talking to a friend about the LE-5 mids I mentioned above, all he could think of was that the (ferrite) magnets had no magnetism. So I checked it out---and, yep, ferrous metal objects, even small ones, don't stick!

Anyone seen such a thing?
Click to expand...

That is very strange and uncommon. Ferrite magnets don't discharge or wear-out from normal usage.

A magnet can demagnetize from being heated, but the "Curie temperature" of a ferrite magnet is 450C / 842F so it would pretty much have to be exposed to fire or similar to get that hot, and there probably wouldn't be much of the midrange driver left.

A magnet could potentially be demagnetized or partially discharged from a strong impact. Like hitting it with a hammer or dropping it on a very hard surface. Maybe the magnet was out of alignment and someone tried to get creative with a hammer? Still seems unlikely.

A magnet could demagnetize due to being exposed to a very strong magnetic field. With Alnico magnets, which discharge more easily in this respect, they can be partially demagnetized simply from overpowering them with lots of amp power when they are used in woofers, etc. But no one would run that much power through a midrange, and ferrite magnets are less susceptible to this to the point where the voice coil would burn up long before the magnet would discharge. But, maybe someone kept them in storage while in contact with another large magnet over a long period of time?
 
The pair came from the LA area. I was wondering if it was possible that somehow they were part of a bad batch that snuck out the back door in Northridge? The back plates were not stamped with a model number.

My dad had a way of bringing home attractive mechanical/electrical things---he did not need to have a reason to bring a shiny object back to the nest, as long as he thought it was cool. I know he never had JBL speakers---that was my domain. Mine were S-1 I think(? )(LE14A/175dlh/n1200), so no mids there. He did have arc welding equipment----those likely have a lot of EMF around them, but probably not enough to depolarize a magnet.

They could have been up against other speaker magnets at some point, but I do not usually think of that as a problematic situation.
 
howgee said:
They could have been up against other speaker magnets at some point, but I do not usually think of that as a problematic situation.
Click to expand...

Generally it would have to be an extremely strong magnetic force to demagnetize the magnet. Bringing a ferrite magnet in contact with another magnet of similar size, or a bit bigger (like a woofer or subwoofer magnet) for a short period of time probably wouldn't have much if any effect. But if it was left that way for a long time (years), then it might.
 
For future reference: Occasionally I store drivers face to face. I believe that I remember that sometimes I feel a slight repulsion as I bring the mounting flanges together. Are magnets better stored (+) to (-) than (+) to (+)? Is it best not to store them if you feel a repulsion?

I have not used them, but I think that we have a JBL-pro repair shop nearby. It would likely cost more than these are worth, especially with dented domes, but should they respond to being re-guassed with a powerful machine? Is magnet material ever faulty out of the factory?
 
Talking to the same buddy again, and we decided that a likely scenario is that the drivers (somehow) never made it into the magnetizing fixture after being assembled , and that they were never part of an assembled retail system at all. The logic partly being that it would be much more difficult to assemble and align a driver once it was magnetized, so likely they are assembled, then magnetized, but in this case----not.
 
You must log in or register to reply here.
Back
Top Bottom