Quote: The big unaddressed question from the OP is "What constitutes 'relatively clean'". At 85db in a mid-sized room, most 8" woofers are distorting horribly. The good news is that the ear isn't terribly sensitive at such low frequencies, so you don't necessarily hear it ...... Until you switch in lower distortion (read larger) drivers to handle the bass.
That's really a loaded statement.... 85db is nothing. On todays drivers with stiffer cone materials, quality spiders and surrounds We really shouldn't be looking at horrible distortion... of course, there was nothing said about the frequency that distortion was measured at, nor the normal excursion limits of the driver measured, its true that woofers normally have higher distortion than smaller drivers, but overall, today, you just can't apply the above statement to "Most" 8 inch woofers.
Tim