Over excursion

I have a customer that had a box built by one of my employees.  The tinsel lead keeps seperating from the connection point, Its actually breaking the little tab that the tinsel lead is soldered on to.  They are infinity dvc 10's and it is only happening to one of the voice coils.  I thought at first that the box was too small and over excursion was the culprit so I added some polyfill and replaced both subs and it sounded 10 times better but now it has happened to another sub.  Can anybody help me figure out what else this might be?

Problem is likely that the lead is to short for cone movement.  Techinically over driven, the cone is moving further than the lead will allow.  Weather this is caused by by wrong box, exessive power or poor quality control can only be determined by you.  As for puting polyfill into the box, you are foolong the sub into believing its in a bigger box, and would likly make the situation worse.

A larger box (if sealed) will have a "less springy" or "softer" air-mass within it, and because of that, the air mass will have less control over the cone movement... You need to go the other way, and make the box SMALLER... As Steven pointed out, adding poly-fill (or any stuffing, for that matter) will actually make the box "appear" larger to the woofer, so adding that stuffing actually exacerbated your problem, it didn't help you at all... How big is your enclosure right now? Is it the size recommended by Infinity? Is it too big? IS IT TRULY AIRTIGHT!?!? I capitalize that, because that's a big issue. A "sealed" box with air leaks behaves the same as a vented box - a too-small vented box, tuned too low. Add this to running the woofer without a subsonic filter, and you are looking for problems... Check these issues. It seems to me that it is most likely the box, as you said you have replaced the woofer, and the issue continues. Are you overpowering the woofer, i.e is your amplifier within the rated power specs of the woofer? Is the bass-boost cranked? How are the rest of your settings? LOTS of things could be happening here, but I suspect your enclosure, first and foremost.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."