JBL 4412's: Tamed by tubes

Naptown Rob

Ponographer
Y'know - I never really liked these things. They hung in my studio for years. The high end always bothered me. Eventually the woofer surrounds rotted & they were replaced by a similar member of the JBL family which I also never really liked. Cut to several years later when - don't know why - they're in my house. Then they're in my storage unit. Finally decided to refoam them for use at my wife's birthday party.
Apparently the problem all these years is that they weren't powered by EL34's!
Much better. Now what? I've got too many speakers...
 
Keep em
I started out with a pair of 4311's and a Leak Stereo 50 EL34's.
Running L112's, but one day Ill find another of the 4311's
Different speaker, but the same holds true.
bob
 
Y'know - I never really liked these things. They hung in my studio for years. The high end always bothered me. Eventually the woofer surrounds rotted & they were replaced by a similar member of the JBL family which I also never really liked. Cut to several years later when - don't know why - they're in my house. Then they're in my storage unit. Finally decided to refoam them for use at my wife's birthday party.
Apparently the problem all these years is that they weren't powered by EL34's!
Much better. Now what? I've got too many speakers...

How old were the when you first heard them? I ask because the Ti tweeters have a piece of foam that is supposed to damp the metal dome, but it shrinks fairly quickly and eventually rots like the surrounds. Only cure for the harsh is new foam, although others have tried backing off on the L-pads.
 
My 044Ti foams still looked pretty good when I inspected them, although they did leave some residue on my fingers. I've read some threads before on replacing them, but what kind of foam would you use for that?
 
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My 044Ti foams still looked pretty good when I inspected them, although they did leave some residue on my fingers. I've read some thread before on replacing them, but what kind of foam would you use for that?

I can get a picture of the foam up for you. That is the best I can do.
 
How old were the when you first heard them? I ask because the Ti tweeters have a piece of foam that is supposed to damp the metal dome, but it shrinks fairly quickly and eventually rots like the surrounds. Only cure for the harsh is new foam, although others have tried backing off on the L-pads.

Are you sure about that? I don't recall ever seeing foam on them (I'm @ work, they're @ home) & I don't see foam on the 052ti images I find...


JBL_L60T_Stereo_Speakers_Tweeter_web.jpg
 
It's a cylinder of foam that's under the dome; you need to take them apart to see it. When new, it presses against the underside of the dome, but eventually it gets flattened and crumbles. It can even get into the voice coil gap.

attachment.php
 
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What were they thinking? Foam?
By the time these were made the disintegration of foam was such a very well documented phenomenon. It's effectively planned obsolescence.
Of course they used it on the woofers, too, so....
 
What were they thinking? Foam?
By the time these were made the disintegration of foam was such a very well documented phenomenon. It's effectively planned obsolescence.
Of course they used it on the woofers, too, so....

Typical JBL junk. I suggest you disconnect them and take them to the curb immediately. Please let me know when trash night is........:yes:
 
Typical JBL junk. I suggest you disconnect them and take them to the curb immediately. Please let me know when trash night is........:yes:

You can throw 'em in the back of your truck with all those Mac amps you're taking "to the recycling center"....
 
Foam from 044ti kit.
 

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Tubes always seem to take the edge off. Mine sounded great. You do need a quality ss amp, however.
 
The measurements are slightly rough:
http://www.audiokarma.org/forums/showthread.php?p=5151861#post5151861.....
If we can get some sort of collaboration on material source and foam cutting/punching I'm all for it.

Ah, yes; thanks. I think the simple approach would be to get some adhesive-backed foam weatherstripping (the light grey foam like that in your photos) of the correct width and thickness, then just use a round die to cut "columns" out of it.
 
If I can get links to what may be the right die and material I will punch some out for us. I've never worked with foam so I fear that metal tooling may not work right.
 
That would be awesome! I think the gray open-cell adhesive-backed foam is the way to go; better too soft (underdamped) than too firm (overdamped). My local hardware store may carry it; it looks generally like this:

foam-1286904708.jpg


Hmmm ... maybe this one?

http://www.fastenal.com/web/products/detail.ex?sku=0601436&ucst=t

1" wide:

"A soft comfortable and low density foam for sealing out air, dust, and light when compressed 30%. Consistent thickness and good compressibility for an excellent vibration-resistant seal. Also can be used to help cushion, damp sound, and absorb vibration in electronics. This single coated foam tape is charcoal gray. Length 9 yards; 3/8 in thick."

But the price ... ouch.
 
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While I'm with you guys in theory (replacing old worn out foam may bring back proper damping of the Ti dome), I am unsure if the risk of damaging such rare and valuable drivers warrants mucking with them. Has anyone done any scientific measurement on the driver before and after to really quantify the results?

Seems like we're drifting pretty close to " if it ain't broke" territory here....

Jblnut
 
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