How does a speaker blow out?

It was a woofer, so the low power seems to be the issue.  The amp is triode/ultralinear switchable and I liked the triode mode better.  I should have switched to ultralinear (i.e., 45 W) if I wanted to play loud, it seems.

The difference between triode and ultralinear is not going to be enuf, I think, to protect your speakers when your blasting away. Depending on your stuff the difference might be only about 3db. Save your speakers, your ears, and your neighbor's good will - keep the volume down. :-)

       What Erik said (regarding clipping), but: after a x-over passes that high freq distortion to the tweeter and burns it (typically: open), the energy that no longer has a path that way, is routed to the next highest freq driver, in the circuit.

                  In the case of a two-way: that would be the woofer.

        I lost count of the number of two-way systems in which I found both drivers toasted by an under-powered amp, while in the reconing biz.    Blown x-over caps, as well.

        Though a clipped signal isn't DC; it certainly can do as much damage.

         On the other hand: hearing a, "...most painful noise, coming from one of the woofers", might indicate a woofer that was driven past it's mechanical excursion limit (X_{mech, per Thiele-Small)}, bottoming the voice coil, or: causing it to hit the gap's top edge(s).

         That type of damage usually resulted from boosted/heavy Bass and a vented cabinet, regardless of amplifier rating.

It might have been around 70dB, I wasn't making the windows rattle.  And it was organ music!!!  LOL!!!!

I appreciate all the info!

Another possibility is simply a defective product. Even with really good quality control on the production line, there can still be hidden issues that show up only after a product has been used for a while.