The higher the excursion levels, the more IM distortion there would be...

I do agree with you though about some car speakers. Some component systems have a crossover point of like 6,000 Hz with the tweet, and the most common low xover is 80 Hz. So it is really excessive. However, most of these designs aren't exactly ideal anyway. 6.5" woofer up to 6 kHz? Gimme a break.

I'll be running Seas Excel 7's from 60 Hz to 1.2 kHz in my car, coupled with horns... It's a wide band for the excels to do, but I'll be running four of them so there will be less excursion.

When you talk about this, don't just confide it to home and car systems, either. Look at most pro systems... 2-way units running 15" woofers up to 1.5 kHz. So the woofer is delivering 40 Hz tones at 10mm p-p excursion while trying to throw out 1,500 Hz signals as well. No matter how well the design, this becomes a problem.

"Home audio - 2 way systems - It seems these systems are highly
compromised at high spl for the said reason, but people insist
on building them? The only reason I can think of is.. they don't
crank the tunes?"

Cost is one... Complexity is another...

Adam