Repairing woofer?

[beenthere]

Hi all, nice forum.
I have a pair of JBL 4312 control monitors that when I crank up, I get a popping noise from one side. I have examined the spider and voice coil for any signs of separation but its good. As I manually exend the cone I notice on the white coating of the 2213h woofer a circular crack about midway of the cone. When I release, the crack disappears. Examining the cone from the back I see a permanant circular crease in the cone and it is now apparent that the cone does not maintain uniform stifness and flexes under moderate power. can this woofer be repaired with a mesh and glue/resin procedure or will the added mass affect the sound. Reconing it is very expensive.

I also see alot of 123a woffers on ebay pretty cheap. these were used in 4310 monitors and look identical from the front. Is there a difference between these 2 models?

[boputnam]

BT...

I can't know what is going on with your existing 2213H, but it does seem a recone is in-order.

The 123A-1 (L100 and L100A) will fit right into the 2213H baffle cut. However, they are different from the 2213H, and JBL notes "Exact Acoustic replacement? No." However, the 2213H is recommended for swapping into the L100A (do both cabinets), but these are different polarity and you must cross-wire the 123A-1 if you use these in 4312 cabinets. Replace both.

If you replace both, you should be acoustically OK - but be aware, as with any used goods you are acquiring a history you know nothing about. Caveat emptor... :yes:

Use the Search button to study more on all these topics...

[GordonW]

Try this before going to more drastic measures:

Take some Elmers white glue. Push the cone in the manner you described to open up the crack from the front, and rub in some glue into the crack, making sure you get all of it in there that will go. Then, take the same white glue, and rub on moderately heavy (make sure you cover it well) layers onto the crease in the back of the cone, and about the surrounding 1/2" to 1" around it as well. Be sure to rub it in well, you want it to penetrate into the paper well! Don't use any paper, cloth or other fiber on top of the glue; it really shouldn't be necessary.

I've oftentimes had this procedure VASTLY improve the structural integrity of a damaged cone. I just repaired a pair of Ohm 8" woofers this way, that the owner was just about ready to trash (some idiot repair shop, across town had man-handled the cone, after he took them in for refoaming). Worked great... I was able to get the thing to act just about as stiff and strong as it was originally. White glue is great stuff on paper!!

Regards,
Gordon.

[beenthere]

Thank you for the replies. Didn't think glue by itself could work to stiffen paper. Gonna give it a try. If that doesnt work, I will try a few thin strips of fiberglass matt in a cris-cross pattern from the back of the woofer.

[boputnam]

You will be changing the moving mass of the cone. You are better-off to get a replacement pair, or recone those.

[GordonW]

Unless you empty gobs of it on the cone (far more than is necessary to fill in the cracks and creases), the white glue will NOT change the moving mass of the cone, enough to be audible. Heck, I doubt you could even MEASURE the change in T/S parameters.

Believe me in this, I've done it... we're talking about fractional-gram mass increases, in a cone mass that's approaching 75-80 grams. Driver-to-driver variations of 5 percent in parameters, are commonplace, even in JBL drivers... in comparison, the change we're talking about here, is in the order of 1 percent, TOPS...

Regards,
Gordon.

[boputnam]

Originally posted by beenthere
...I will try a few thin strips of fiberglass matt in a cris-cross pattern from the back of the woofer. Gordon, this is what I was replying to, not your suggestion of dabs of white glue (not endorsed, just not argued here...). We're not making sailboats here... :smthsail:

[GordonW]

Well, here's my take: If the cone is cracked, he's not losing anything trying to fix it with white glue. Won't make any difference how much white glue he uses, if he decides to recone it later.

And the nice thing about white glue, is that once you fill the crack from the front, you can take a damp cloth, and clean away all the excess white glue... and when it dries (clear), it'll pretty much be INVISIBLE that you did anything. Now, on the backside of the cone, you'll be able to see a "shiny spot" if you load it on back there... but really, there's already a crease back there, we're not talking about pristine here in the first place. Just an attempt to get it to work properly again...

Regards,
Gordon.

[Mr. Widget]

I agree with Gordon on this one.

I have an LE15A that has a clean slice in the cone. Someone before me repaired it with yellow woodworkers glue (white glue with an additional resin added). They did an ok job aesthetically, it could have been better, but functionally the cone has performed flawlessly for years. White glue would have worked just as well.

Widget

[boputnam]

:spin:

The only idea I argued against wrt changing the mass of the cone, was using fiberglass strips. That could end-up shifting the center of mass, as well. That can't be a good idea. But, I surely am dumb about all kinda things.

I think you should cover the entire cone with mystical white glue... :nutz:

Then again, since these are not irreplaceable (but the longer we procrastonate, who knows...), why not get 'em reconed? Or maybe you live on a deserted island...

[DavidF]

A curvilinear cone with a “knee” in the circumference would give me much concern. There is a certain amount of flex given in this cone style that effects the overall response. Based upon beenthere’s admission to exercising his speakers, I would have to think through how well I could repair this crease and get back to the flex parameters of the original design. More so with these woofers responding way up into the midrange with limited restraint from the crossover. Always worth a try, no doubt, but I would suspect that a good amount of luck is involved in getting the two drivers close on spec with the repair effort, making a recone unavoidable.

DavidF