I am actually having a hard time digesting this. If you
would like to try re-explaining this to me I would be obliged. I am not sure
how I want to counter to those statements.
My comments are entirely based on equal loudness contours. A deep bass
pure tone at 20 Hz (with no harmonics) is quite soft sounding at 100 db SPL
(in fact you may hear rattling of windows etc. louder than the pure tone - i.e.
you are more sensitive to harmonics or vibration induced by the 20 Hz tone).
Basically we hear 1 KHz tones with some 60 db better hearing sensitivity. As
you get louder and close to 130 db SPL at 20 Hz then the equal loudness
curves flatten significantly and that pure tone would sound as loud as 100 db
spl at 1Khz ( a mere 30 db drop in sensitivity as our hearing response
"flattens" as you go louder) As you can see from those curves - even a
tiny bit of harmonic distortion (say 5%) from your sub on a 20 Hz pure tone is likely to be more audible than the test tone itself - just because of our poor hearing sensitivity at 20Hz.