Originally Posted by basshead81
So you are saying you can tell a difference between 10% and 20% 2nd order THD? When I played a 15hz test tone at 110db, I herd nothing but the walls and cabinets in the house pulsating, the subs were quiet...I turned it up to 115db still no audible change in the subs, but when I turned it up from there the subs did not raise the spl levels and they started to make audible noises that sounded like distortion. I am not arguing with you, but I am just trying to figure out why you specify 10% thd in lower order harmonics is clean bass? Why does cea-2010 allow such higher low order thd levels?
It is all about the audibility of distortion.
One factoid - most bass musical instruments produce more low order harmonics than fundamentals. Since the harmonics are also quite a bit more audible than the fundamentals, that is most of what you hear.
So adding even more low order harmonics doesn't make that much change to what you hear, since there is already so much of them present in the recording. The same is generally true of SFX in movies.
In contrast high order harmonics stick out like sore thumbs.
Most distortion in a well made subwoofer driver is due to the active region of the voice coil moving out of the magnet's active gap. Whether the magnetism in the gap falls off slowly or rapidly is up to the designer. The more rapidly the magnetism in the gap falls off, the more higher order distortion is generated. If the cone hits a mechanical limit, then you obtain a similar effect.