Originally Posted by bossobass
In the 1st 2 octaves HD is of little consequence and actually adds to the experience, IMHO, as most of it is subsonic, but from 20-30Hz, high THD is definitely audible. Whether or not it's offensive or pleasing is in the eye of the beholder as many 2 channel tube amp buffs and 2" analog tape recordists will attest.
It depends on the spectral breakdown of the harmonics. The higher order and odd order stuff is subjectively perceived as more offensive.
Usually in a sealed subwoofer, the majority of the THD at VLF is derived from the 2nd order harmonic component, which is not terribly offensive subjectively.
Most of the subs I've measured have shown progressively less sound pressure from the upper order harmonic components, typically following a -12 dB/octave slope. So the 10th order and higher stuff is usually -40 dB or (much) lower relative to the fundamental.
But I have seen an interesting exception lately which does speak strongly to the value of the CEA 2010 standard.......