For the first time I had a chance to crank up the amp and drive the speakers at a loud listening volume, but not so loud as to be uncomfortable. We put on Hector Berlioz's Symphonie Fantastique, which I was stunned at the dynamic range of that CD.
Toward the end of track 5 we had the left woofer make a crack or popping sound, which I assume was the voice coil slamming into the back of the magnet structure.
This surprised me because my amp is only 60 Watts, so I would not think that it was a simple case of over driving it. The right woofer played fine and subsequent tracks on other CDs occasionally did the same thing to the left woofer. So, we backed down the volume.
These woofers had a bad time when they were shipped to me and both cones and the domes in particular got some damage when the plastic tie-wraps that held them together broke enroute. I am now thinking that it may be time to bite the bullet and have them reconed.