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!
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.
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..
..disconnect these, remove woofer fastening screws (four) and lift the woofer away from inside the front half.
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!
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:
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!
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.
And that’s it, looking all good for installation.
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 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).
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 :)
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/