JBL L40 10' woofer surrounds?

My first refoam job ever was on a pair of L80T and 4410 woofers (all 4) with Cobb surrounds. At the time I didn't have any way to play the tone CD. I simply set the speaker on it's back, cleaned off all the old foam, then gently pushed in on the cone to see if there was any rub. There was none. I could move them off center and make them rub, but they always came back when released. Glued the surround to the cone, let it dry, felt again for rub, then glued the outer edge to the frame. Came out perfect.
 
My first refoam job ever was on a pair of L80T and 4410 woofers (all 4) with Cobb surrounds. At the time I didn't have any way to play the tone CD. I simply set the speaker on it's back, cleaned off all the old foam, then gently pushed in on the cone to see if there was any rub. There was none. I could move them off center and make them rub, but they always came back when released. Glued the surround to the cone, let it dry, felt again for rub, then glued the outer edge to the frame. Came out perfect.

It has been my duty with cast frame JBL's that one installs the new foam to the frame first. This is due to the fact that if you glue the cone first there is a definite possibility that gluing the cone first you can still have a misalignment issue and and that will affect how the foam fits properly into the recessed frame area.
The cone can be better "tweaked to fit tha the metal frame which can fit only one way!
Again, these are mt opinions, object may appear closer than they actually are......
DC
 
Cool to see more L40s getting some AK love. I refoamed a pair about a year ago using the tone centering method. I used a tone generator on my phone and just connected the headphone out to the driver. Worked great :) Rock on !
 
It's been awhile since I did mine, but if I remember correctly, the surround had to be stretched slightly to install under the cone, and the cone itself fit perfectly inside the "roll" of the surround, leaving virtually no room adjustment. The outside, on the other hand, had a gap between the edge and the frame for adjustment if necessary.

That, and I watched several of the JBL refoam videos on youtube, and most if not all glued the surround to the cone first, so I followed their lead.

But I'm no expert - it was my first and only refoam job. I might have just got lucky.:thumbsup:
 
So long as it was a successful re-foam and you now have a new skill is what matters!
Congrat!
DC
 
  • Second, assuming that a couple of you feel that I should go ahead with the refoaming and see how it goes, am I being wrongheaded by thinking about gluing foams onto the tops of the cones rather than underneath, and that way not having to worry about possibly damaging the cones by trying to remove the remnants of the old surrounds on the underside? Or should I just proceed with caution, clean it up and glue under the cone?
Please don't do this. The foams are designed to be glued to the rear of the cones. Some will tell you it makes no difference in the sound of the driver, but it does make a difference in the appearance, and hence the resale value of your JBL speakers. Foams glued on the front are not historically accurate and detract from the appearance, and value, of your vintage JBL speakers.

Same with the dust caps. Leave the original dust caps in place and use the test tone method recommended by Rick Cobb (and mentioned by others in the thread). His standard refoam kits come with an included CD with a 30Hz test tone. The original duct caps will have the same time acquired patina to match the original cones.

There is a local "professional" repair shop near me that refoams a lot of speakers. For most, cosmetics may be of little consequence, but for me, especially when it comes to JBL drivers, authentic, original appearance matters. I see lots of "restored" vintage JBL speakers on the local craigslist with improperly installed foams and incorrect dust caps. To me, they look like a total hatchet job and I wouldn't touch them with a 10' pole. I'd much rather buy speakers with completely rotted out foams and do them right myself.

If you don't feel comfortable doing the ob correctly, find someone who will.

That said, it's not really all that hard to do it right. Within the last two moths, I have refoamed two pairs of JBL 116H1 woofers. These are baby brothers to the 127H1 woofers of your L40s. I have large hands, and on the small 8" drivers, it was a bit tight in places getting at the backs of the coanes, but it still wasn't that difficult. I think the larger 10" 127H1 woofer would be even easier.

A couple tips:

The Rick Cobb refoam kits come with a small bottle of glue. This appears to be standard Aleene's Tacky Glue. This works fine and dries clear, but it takes quite a while to set up and cure. I used it for my first pair of 116H1 woofers, and it was slow going. It took quite a while to set. I glued the foams to the cones first (as recommended in the instructions from Rick Cobb), let the glue cure overnight and glued them to the frames the next night. let them again dry overnight before installing them into the cabinets on the third night. Probably over cautious, but eveything I read on the original Aleene's recommended letting it cure for 8 hours.

For the second pair, I picked up an 8 oz. bottle of Aleene's Fast Grab Tacky Glue at a local Micheal's Craft. It sets and cures faster than the standard Aleene's, but still gives you plenty of time to make adjustments, if needed. With the fast grab, I was able to glue the foams to the cones and frames in a single evening (cones before dinner, frames before bed, ready to use the next morning). Not a big deal, but it sped up the process a bit.

Aleene's, both regular and Fast Grab, is good stuff and it dries clear. If you have a Micheal's near you, they stock both types, and with the typical 40% off 1 item coupon, an 8 oz. bottle of Fast Grab (enough to do several pairs of woofers) will run you a little over three bucks.

The other word of advice I can give is don't use too much. A small continuous bead is all you need. On the first pair, I used too much and some oozed out from behind the cone. I wiped it off with a damp cloth, and it dried clear, but it's still visible if you look closely. Nothing terrible, but it doesn't look as professional as the second pair I did. The second pair came out perfect.

Good luck no mater how you plan to proceed. The prices on vintage JBL speakers keep going up, even for the more modest models like the L36, L19A and 4301B I have restored. This makes taking the time and effort to do an authentic restoration time well spent. Doing it right isn't really that much harder than doing it wrong and will enhance both the appearance and value of your JBL speakers.
 
My first refoam job ever was on a pair of L80T and 4410 woofers (all 4) with Cobb surrounds. At the time I didn't have any way to play the tone CD. I simply set the speaker on it's back, cleaned off all the old foam, then gently pushed in on the cone to see if there was any rub. There was none. I could move them off center and make them rub, but they always came back when released. Glued the surround to the cone, let it dry, felt again for rub, then glued the outer edge to the frame. Came out perfect.
I did the same thing, mine centered up perfect, it was fairly easy, took some time to get the old foam off of the frame and the cones, I used Ricks surrounds also, there's a few vids on youtube that helped , I did some 125A's
 
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I'm done. I successfully refoamed my L40s. Unbelievably, they played afterwards. Thank you, Rick Cobb, and all o' y'all, for the advice and encouragement. These methods really do work.

I have now listened a fair amount to these speakers. My original intention was to fix them and sell them. I have been listening to Magneplanar SMGa's for years, though, and it's hard for me to abandon their sound. I've been working on them also, and in fact interrupted that project to finish these. So these have served as my main listening speakers for a couple weeks. They're great, for what they are. Really tons of bass, too much for my taste, and a bit of a hole in the midrange, compared to what I'm used to. They do put out a prodigious amount of sound, however, that only gets better as they play louder!

I don't think that I can legitimately keep them though. I think I have to stick to the original plan. They've been a great learning experience in so many ways. But a one-bedroom apartment is perhaps not the best place to have three sets of speakers. (I know I haven't mentioned the third set.) So I think... I'm gonna let them go. I'll probably put them on eBay later today, or else later in the week when I have time.

I'll put some pictures in here. You can see that one of the woofers was in pretty rough shape, not just the foam, but the cone itself was somewhat crumpled on one side. I did my best to flatten it out, and glued it carefully to the surround.

Next up: finish the Maggies. Regluing the wires. Those, I'll keep though. I'm addicted. :)
 
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