I recently had (2) jbl 2406h1 comp drivers fail. They still show continuity and read 4.6 ohms like they are supposed to but do not work. What causes this? I've used these drivers about 5 years now and never lost even one. These are from mp412 cabs on monitor duty. Were not overpowered. The coils dont really look burnt. I have never experienced this before with them beeping out good but definitley dont work. The two "sonic guard" bulbs in both these boxes did not blow.....wonder why the diaphragms did?