JBL L26 Refoam question

I just picked up a decent set of L26's that need a refoam. I called Jamac here in Portland (which seems to be a reasonably well respected speaker repair place) and they said they would have to remove the convex dust cap and most likely replace it with a new (non convex) dust cover. I think that would look bad and I could probably do that myself. Is he right is that the only option?

I've read on here before where people use some frequency of tone (perhaps 60Hz) and can refoam them that way. The guy at Jamac says that is a particularly bad idea with JBL because they are high quality and built to tight tolerances. What wisdom/suggestions are out there in AK land?

I did a set of L36 without removing dust cap with a 30 hz tone and yes they are a little tricky. I actually had to do one twice due to VC rubbing but I got it without shimming.

What reputable speaker repair shop would even consider defacing those special inverted dust caps?:nono:

Nope. I did my own L26s' L125A woofer refoams. Not hard and no need to cut up the dust cap.

It's not hard but that's the only refoam I had to re-do on one of the woofers.
I didn't use the test tone for too long so make sure you use the tone until glue sets in.

Mine were refoamed before I bought them, without the dust caps' removal. No rubs here.

Sure would like to find someone in Oregon with the tone generator and the know how to help me with this. Hmmm... I'll have to think about this. I would hate to trash the original look of these, as I think I can make the cabinets look great. Thanks folks.

Watch some YouTube videos ...

Shimming is virtually fool proof. You can carefully cut most of the dust cap, leaving just a bit to act as a hinge. Lift the cap like a flap and insert the shims. Once the surround is completed, re glue the dust cap to it's original position. When the glue dries, it should be virtually invisible.

I did this on my AR LST2 woofers and you cannot see where the dust caps were cut.

cfinchrist said:

Sure would like to find someone in Oregon with the tone generator and the know how to help me with this. Hmmm... I'll have to think about this. I would hate to trash the original look of these, as I think I can make the cabinets look great. Thanks folks.

Click to expand...

You can generate tone in your computer.
Just download audacity.

GD70 said:

Shimming is virtually fool proof. You can carefully cut most of the dust cap, leaving just a bit to act as a hinge. Lift the cap like a flap and insert the shims. Once the surround is completed, re glue the dust cap to it's original position. When the glue dries, it should be virtually invisible.

I did this on my AR LST2 woofers and you cannot see where the dust caps were cut.

Click to expand...

Nothing's fool proof, especially around sharp knives.

I guess the question is have you ever refoamed a woofer before? If not, I would find some cheaper speakers to practice on. Not that those are very expensive but you do want to get them right. My first refoam was on a pair of Boston Acoustic A60's. They were cheap and came out good.

I've done several of the standard dust cap type, but not these. I may see if there is something on youtube specific to these JBL's. If I can find no way to comfortably do these the right way then I guess I could do the rip and tear method prescribed by the repair shop (in more accurate words...the non original results method).

Speaking of `rip and tear` methods....http://www.audiokarma.org/forums/showthread.php?t=551838

Get the foams and bring them up here. I have a nice tone generator setup for refoaming. Works very well.

blhagstrom said:

Get the foams and bring them up here. I have a nice tone generator setup for refoaming. Works very well.

Click to expand...

Awesome! Will do. Thanks Blaine.

Seems unnecessary to bring this up in relation to re-surrounding JBLs but let me remind you that Rick Cobb sells his surround kits with a CD that generates the tone included. He knows JBL surrounds better than anyone else I know and has many here who praise his products and customer service. I am but one of these!

http://www.audiokarma.org/forums/showthread.php?t=492477

Mystery said:

You can generate tone in your computer.
Just download audacity.



Nothing's fool proof, especially around sharp knives.

Click to expand...

I said virtually, not guaranteed. You must use an xacto with a #11 blade. Much more control cutting than with a straight edge razor, which I would not recommend. If the OP doesn't trust his cutting skills, then by all means, go the tone route.

Although the original is concave, there are some working with JBL's that feel there is not much difference in putting on a convex dust cap with this woofer.

However, the tone method is pretty straightforward and can yield excellent results if you take your time and do a good alignment. I clean and glue the new surround to the back of the cone first, making sure its evenly spaced around the circumference. Then I run the tone at low amplitude and clamp the outer part of the surround to the frame with medium binder clips or large clothespins, whatever will fit properly over the frame edge. If you encounter any distortion with the tone, unclamp, re-center, and clamp again.

I usually clamp at 90 degree, then 30 degree intervals, all the while ensuring the tone runs true and clean. At that point I know the voice coil is clearing the gap. Then unclamp 90-120 degrees of surround, glue and reclampm testing again with the tone. Repeat twice till all of the outer edge is glued down, then replay the tone one more time to be confident the voice coil remains centered. I can even push the volume a bit as well.

Once glue is 24 hours cured, then remove clamps, play again, and if everything is good, re-glue the original neoprene gasket (you did carefully cut under it and saved it, right?) to complete the OEM look.

my experience with decade L36....

I took the chance on the Simply speaker method with their surround kit and instruction video. No shims and no test tone. The prep took hours to completely remove the hardened glue from the aluminum frame.
First step glue the surround to the cone, underside for this woofer, and let it set. It is true that the cone wants to center on its own once the suspension of the surround supports it. The heart stopping part was gluing the surround to the frame because the first 30-45 secs of the process the surround tries to curl up from the moisture of the glue, but don't panic just keep working the surround in a circular motion testing the suspension for VC rub during the setup. Soon enough the surround will stay tacked down and cure in place with no problem.
Maybe I got lucky or maybe the method does work most of the time if you take the time to prep and work methodically.
One thing I almost goofed up on was attempting to get the outer edge of the foam to fit within the step that is cast into the aluminum frame. The step is there to allow the foam to be flush with the frame and allow the black trim pieces to lay flush with the outer most ring of frame that is visible on the baffle front. Forcing the foam within the step was a BAD idea and caused VC rub while i was gluing the surround. Luckily i has able to adjust before the glue tacked beyond working time. After the glue cured I trimmed the surround to fit the step with a blade and the trim fit back on nice and flush to the outer frame lip



The last pic the surround is not glued to frame - (looks way off center)

Hi
I have done L26 woofers and a number of other woofers with special dust covers without a problem. Actually I almost never shim. I use the battery method and allow the voice coils to self center while the coil is being lifted up (with the speaker on its back.) First the surround is glued to the cone and allowed to dry. Then a AA battery is connected to the terminals to extend the cone and surround outward. The glue is applied to the frame while the surround is being lifted by the DC of the battery. The battery is disconnected and the surround drops onto the glue. The clamps are applied to the surround and I test with the 30hz tone using my PC and an online tone generator. If there are no rubs then it is allowed to dry. If it rubs then the surround needs to be slid around to where it does not before the glue sets. After it dries I use some tone sweeps to make sure but I have never had to redo a completed surround.