JBL C1 woofer foam repair

The woofer elements of my beloved JBL Control One speakers have been badly in need of foam surround replacements for ages and recently, I finally decided to take up the project. The foams started “decaying” many years ago, but by now they had already become almost but dust. Lightly poking any part of the foam, or moreover what little there was left, just made it crumble away!

The situation to boot with.

30€ re-foam kit from Ebay, a few items from the toolbox and the replacement project was a go!

Intro bla bla

Without giving much thought for the fact that this was my first time ever doing such a repair, I decided to turn it into this tutorial-ish post. Based on experience gathered, I’d estimate each speaker requiring around 1.5-2 hours of work. This is spanned over a few days as glue needs time to dry etc.. So in other words nothing too bad either way if you have, say, a few evenings to spare.

If you’re a first-time speaker repair n00b like me and plan to use these instructions as a generic guide, I’d recommend taking them with a pinch of salt. I got perfectly fine results with the routines presented but, say, if your tools are different its very likely that you need to adapt/improvise some work stages.. And even if repairing a pair of C1s, what you have simply might be different. Considering how long they have been in production, its very likely that mechanically alternate woofer or enclosure designs have been used (<- that’s me guessing).

I certainly recommend that you read through prior getting down hands-on, just to have a picture of each work stage and the overall process. The standard “you break it, don’t come crying” DIY disclaimer applies, of course. With speakers, all it might take is a simple slip handling a screwdriver.. I usually approach new areas of DIY out of curiosity, tearing stuff apart to see what makes it tick and all that. Had I broken my C1s in the process, no problem there. Chalk it up to ‘learning experience’ and get a new pair. Suggested mindset for any n00b DIY repair ;)

One last thing before we start: Most important part of any repair is to have some good music to accommodate! My repair sessions were winged by Trisector’s Hustle Audio podcast and Compost Black Label Sessions #161. With the music in order, let’s get busy.


First up, remove front metal grille (if installed) and the six screws underneath. On my speakers there were dabs of hot glue on both of the long edges, and to separate the front and rear halves somewhat forceful prying was required. I got mine open by placing fingers against both halves and then using thumbs to push the halves apart.

Prying apart the case halves, my finger technique illustrated. Nevermind how I managed to take this photo.

Dabs of hot glue on both sides to fasten the case halves.

Since the woofer needs to be removed, it’s good to make note of its cable connections. In my case, it was the standard red/black approach..

Cable connections. Red for + and black for – on the woofer.

..disconnect these, remove woofer fastening screws (four) and lift the woofer away from inside the front half.

Woofer removed from case.

Shimmy shim yaa

In order to ensure that the voice coil doesn’t get realigned while repairs are under way, it needs to be secured in place with paper shims. My foam kit came with some readily sliced ones, but equally I could’ve also just cut them from a sheet of A4. If you’re going for the latter, the suitable thickness depends on the speaker and a little experimenting should reveal what works. You’ll know what’s right for sure, once you’ve covered 3/4 of the coil and notice the last one doesn’t fit ;)

Ok so to insert the shims, the dust cap needs to be opened. Using a sharp hobby knife, carefully work around the base of the cap but DON’T cut it all the way. Leave a small portion uncut, this works as a “hinge” which guarantees that the cap alignment will be perfect during reassembly. Also beware not to cut too deep, it could be that (unlike on my woofer) your speaker has the coil very close to the cap!

Cut open the dust cap, carefully working around the base of the cap..

.. but don’t cut all the way!

Shims inserted around the voice coil.

In my case, the shims were actually required to realign the coil. Having had the speaker in use with most of the foam gone, the coil was misaligned and made some very audible dragging noise at higher volume levels or if fed with non-hipassed signal.

I don’t want to scrub

On to the most boring part of any repair project, as in ‘cleaning away all the old crap’. Like with proper paint jobs, here too a clean surfaces are a big part of getting good results. Armed with the scrubbing / scraping tool of your choice, first remove bigger chunks of what’s left of the old foam. Remember to ensure that none of the loose bits get inside the voice coil!

For this stage, I used a flat screwdriver, a paint removal scraping tool (a standard carpet knife razor blade mounted to a handle in a 45-degree angle) and one old sock :). The metallic woofer frame gets it first:

Start with the biggest chunks..

..and continue scraping until most of the paper+foam+glue goo is gone.

My speakers also had a paper gasket on top of the foam. Unfortunately this wasn’t removable without damaging it beyond anything re-usable.

Once the biggest chunks are removed, carefully apply small amounts of your alcohol-based cleaning fluid over what mess remains and let it sit for a few minutes. The alcohol softens the glue remainders, making them easier to wipe off. Be careful not to spill the fluid over the paper cone!

With the glue remainders softened, rub it away with a piece of cloth.

One more scraping pass in my case.

Repeat the above until the frame/ring is clean and then spend a while admiring the clean, shiny woofer frame. Oh, so pretty.

Removing foam and glue from the cone needs very delicate work so as not to damage it. After a little testing, I found that the best approach was to first scrape off glue from the bottom side. This thins down the overall layer, and with most of the bottom glue gone, what remains on the top side can be simply peeled off.

Glue edge on the top side of the cone.

Carefully scrape away foam and glue from the lower side to thin down the layer..

..and once thinned down, the glue on the top side peels off clean.

And that’s it, looking all good for installation.

Woofer case and cone all cleaned up!

Replacements arrive

Not much to this stage of the project really, as it’s mostly about waiting the glue to dry. First, the cone and inner edge of foam are glued together. Second, the outer edge of foam is glued to the woofer frame. Finally, shims are removed, cone is checked for dragging noise and the dust cap is glued back in place. At least for the first two stages, it’s recommended to allow the glue to dry overnight. Remember, if the glue hasn’t had the chance to grip properly, removing the shims “too early” will cause coil misalignment!

The instructions that were included in my kit suggested to first apply the glue on the foam, then insert it in place. However given the very handy nozzle on the bottle of glue included, I decided to ignore the instructions altogether. Not sure about the train of thought with the instructions, but having glue on the foam and then inserting it under the cone sounds like a whole lot of mess to me!

So, following my method.. First, insert the foam in place, checking that it’s aligned neatly with the cone. Next, run the nozzle in-between the surfaces-to-be-joined all around and then, press the halves together for some minutes by gently running index fingers on both sides of the seam. Fast and no sign of glue mess on the surface!

After inserting the new foam, glue can be applied in-between. Don’t forget to press the halves together, two-hand approach works the best!

After allowing to dry overnight, apply the same approach for glueing the outer edge of foam. If the outer edge doesn’t seem to align perfectly with the frame, do not forcefully try to make it look so (stretching etc.)! Any tension in the glued foam will likely misalign the voice coil once the shims come off. Once done, leave the glue to dry overnight (again).

Dust cap glueing in progress..

The next day, remove paper shims and glue the dust cap back in place. In my case, running the nozzle against the cap base (pictured above) proved a clean approach. Hardly any visible glue mess on the outside.

As a final stage, I applied a small layer (ring) of glue around the upper edge of cone. Not sure how much off help it actually is, but I decided to do so just to mimick the factory assembly.. Yeah cheapo :)

..and that’s it, woofer repaired!

Something missing?

Remember the paper gaskets that I mentioned earlier? If your speakers had these and you managed to remove them in one piece, glue them over the foam before assembly. In my case, it turned out that the new foam was thick enough to somewhat match the gasket in height. Once speakers were assembled, the foam seemed to work equally well by itself, and I thus left the task of locating replacement gaskets at that.

So finally.. After all glue has dried up, assemble the speaker and hook it up. Now enjoy the crisp sound of your “brand new” C1s! \o/

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9 responses to “JBL C1 woofer foam repair”

  1. teknojon says :

    perhaps do all the scraping off of old foam & glue before cutting open the dust cap? This will minimise debris getting down into the voice coil – keeping voicecoil clean = very important!! Cheers! :-j

    • Arto says :

      Yeah it’s a good one to keep in mind, really depends on how you want to approach this.

      I preferred having the coil in a “non-moveable” state throughout the repair and went with opening the cap first. This slowed down the cleanup to some extent, as I had to take extra care not to have any debris entering the coil / cup.

      • teknojon says :

        fair! – potentially a best of both worlds option? open dust cap, insert shorter shims (don’t loose them inside!), so perhaps with a tail? (narrower section that will happily fold over) close dust cap, over cautious masking tape application with classy (no residues & low tack) masking tape to hold dust cap closed & deny debris an ingress route. would also minimise chance of knocking off dust cap whilst attacking glue & foam residues! don’t leave tape on for longer than needed re adhesive residues + happily removing the tape. :-j

  2. Ijinkli says :

    I’ve got these exact same speakers. The foam, as you say has just crumbled apart. On one side there’s a scraping sound that must be the coil alignment. That speaker is useless! The coil, I hear, can also be aligned using a dc supply, that won’t necessitate cutting the dust cap. I’m just waiting for my new foams to try this project. Thanks for the how to article.

    • Arto says :

      The coil, I hear, can also be aligned using a dc supply, that won’t necessitate cutting the dust cap.

      If you find a tutorial for this dc supply method, please do share the link :)

  3. Howard Freeborn says :

    on DC alignment

    Another way to centering the voice coil and excellent for removing buzz or rattle is to rig up a 110v/240v to 6v transformer with a pot (wire wound) so you can adjust the 6v a/c side to zero, feed this through a 25 ohm 5 watt resistor, to the voice coil of speaker,adjust volume with pot and listen for any buzzing or rattling and adjust centering until you hear a smooth a/c hum.

  4. John in San Diego says :

    Shimming the voice coils really is an optional thing on most speakers. No doubt it leads to more precise alignment but you can get fine reults by simply hooking up a battery and popping the cone up and down every few minutes during the first hour of drying, as well as careful eyeballing to begin with. Remember your spider is in alignment the whole time, with such a low excursion range you dont have to be that precise. Large woofers with big vmax numbers, shims a must.

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