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Custom earplug speakers for motorcycling; strain relief

I had a set of Challenger custom earplugs with speakers made for me by Bob Weis at The Earplug Company in Florida in 2003. These are terrific for motorcycling, because they fit under your helmet with no need for extra clearance, they block out wind noise better than foam earplugs, and they give you high-fidelity tunes on the move. I use them for motorcycling and also when I fly. The crying babies just don't exist when you play your music through these. (You do have to peel one out to talk to the flight attendants, though.)

I had a professional hearing-aid technician make the molds that I sent Bob. For me it was $50 well spent: the instructions say to be sure to get "past the second bend of the ear canal," but we found out my ear canal is unusually straight. I would have thought I was doing it wrong when I didn't see any bends.

Unfortunately, these earplug speakers are a little delicate and I'm a little rough on them. Besides knocking them around occasionally in tank bags and pockets, I'm forever feeling the wires tug on my ears (meaning the fragile internal connection is also being tugged at) as I do head checks and other maneuvers on the bike. I've had to have Bob repair/rebuild mine twice.

I started thinking about how I could add some strain relief. This page is the result.

Adding strain relief to Challenger-C custom earplug speakers

Here's what the back of an earplugs looks like with no modifications.

The ridge in the center and the depressions above and below it are there so you can "screw" the earplug in and out of your ear. You're supposed to pinch the middle and twist the earplug so the bottom enters your ear canal.

(The red dot is a little stick that seems to be part of the manufacturing process. It's not a tube, just a stick. Maybe Bob can tell me what it's for. The one in the left earplug is a different color.)
 

I've found I don't use the ridge in the center for insertion or removal. Instead, I hold the top and back of the plug and push/twist the bottom into place, then push the top in so it fits snugly where it's supposed to, as illustrated below. To remove them, I reverse the procedure. (Tugging the earplug out using the wire is the fastest route to the repair shop.)

Since I don't use the pinch-bar or depressions anyway, I got to thinking maybe I could use them for some strain relief.

Disclaimers and considerations

Attempting anything like this is sure to void your warranty with The Earplug Company. Bob is a nice guy (he did my first repair during a hurricane, for heaven's sake!) but monkeying with your earplugs and a hot-glue gun is beyond reasonable when it comes to a warranty claim.

Bob also told me this: using adhesives on the wires can prevent him from making repairs in the future. So think about that before you try this. I believe I have this covered: I can melt the hot-glue off the wires if they have to go back in for repair. (This is a reason to use hot glue and silicone adhesive combined, instead of silicone adhesive for the whole job.) This is a calculated risk that I'm willing to take.

Finally, Bob said he thought you could get enough strain relief with a clip like you use on cell-phone earpiece cords - the kind that attach to your collar. Or you can run the wire up over your ear and then down. But for various reasons I thought these tricks wouldn't be effective for me.

Let's get on with it!

So here's what I did: I filled the little depressions with hot glue, then made a loop of wire and rested the two halves of the loop in the depressions. I held them there while the glue hardened around them. Theoretically this should provide strain relief: a tug on the free end won't pull on the delicate connection to the transducer (speaker) inside.

I tried to arrange it so there wasn't too much strain on the wire as it leaves the ear mold and turns upward to the first blob of glue. I also made it so the two blobs of glue aren't connected to each other. Otherwise, movement at the free end would transmit to the other side of the loop, which defeats the purpose.
 

There's just one problem: the hot glue doesn't stick to the outside of the earplug. I don't know what those things are made of, but they're slick and none of the adhesives I had handy would stick to them.

Bob told me that Permatex makes one adhesive that works. I think he was talking about "Permatex O-Ring & Rubber Bonding Adhesive," which is Permatex part number 40413. It comes in a little yellow bottle (1/3 oz.) with a tall black cap and a black label. (Bob, if that's not the right stuff, please tell me. If anybody else knows an appropriate adhesive, please tell me that too. Use the feedback link in the left column of this page. Thanks.)

The idea is not to use the Permatex adhesive in place of the hot glue, but in addition to it. Do the hot glue trick as described above. When it has cooled and solidified around the wires, you can pop the blobs (with wires running through them) out of the depressions. Now dab the depressions with the  Permatex adhesive. Put the solidified blobs of hot glue back in where they came from, and hold until the Permatex cures. Voila! Now your hot glue is itself glued into place. I figure I can still get the wires free (if needed for repairs) by melting the top part of the hot glue, while the rest is still secure. I can re-seat the wires later by melting more glue into the right spots: the new hot glue will stick to the old glue, which is still stuck to the earplug. Genius? Aw, shucks.

This all depends on whether the Permatex adhesive actually bonds to both the earplug and the hot glue. I have not tried this yet, so don't assume everything I've said is true!

Pedantic and wildly speculative financial reasoning - stop reading now!

Bob says I might be ruining his ability to repair these in the future. This is a risk I'm willing to take. I figure (A) the earplugs should last longer between repairs, (B) I can melt off the hot glue if they do need to go back for repairs so he can do his thing, and (C) the amount of money on the table is small enough that I'm willing to gamble. The worst case is a full replacement at $160, with a low probability, as a bet against a reasonable probability of saving one or more repairs at $70 each, plus hassle.