Ah... you are using the Sony XM2020? Nice baby amp. I had the XM4040 years ago, and was still fooling around with the XES M3. Nice amps! I'm not sure if the Xplod is made in japan though, if its top range, it probably is.
Quote of the day from car audio source:
"Under-powering a subwoofer is as bad, if not worse than over powering it. Excessive distortion from a over-driven small amp can quarter the life of a subwoofer. "
Its very commonly known that underpowering subs will shorten the lifespan. Ok, granted that I'm talking about subs, but maybe not mid ranges. Based on the fact that the theory of operation is the same... I would think it applies too.
Having played with 8s, 10s, 12s, 15s and blown quite a few, I practically proved it for myself too.
Case in point - remember about my 3 month lifespan 8" woofers. Any interesting scenario.
I had 800W rms @ 2ohms going into a pair of 12" Inifnity Perfect 12.1. First application was a nice sealed box. The subs were ok. Pumping real hard like never before, SPL comp style. This was in a saloon car.
Interesting thing... subs are rated 350W RMS each. But when I tried going with only 300W, the bass was... yeeeck. soft and limp. Pumping 400W... it suddenly came to life, and giving very very healthy sounds! I reconfirmed that prolonged periods of going with that plock plock sound from underpowering would soon kill the sub. Surprised to fix the problem by simply upping the wattage.
When I switched to a coupe, I had the same setup, but tried to go freeair this time. Of course, freeair needs loads more power than sealed box. My woofers died within 2 months! seems that the sub wasn't powerful enuff to control the excursions, and was clipping and hence underpowering. Voice coil burn.
I didn't dare to believe. Spent money to buy similar woofers, and did a straight replacement. New pair died within 4.5 months. Wa lau. Confirm plus stamp liao!
Harmonics.. area under curve, all that... I return to my acoustic engineering and engineering simulation teacher already,... but just contributing from experience and the practical side of things...
Your analysis is very clear, I like it.