[MikeyMouse]

Why do subwoofers even some of the best one produce distortion like noise when you listen to the driver closely?  Are these really the distortion from the driver or this is how the low frequency sounded without all the high frequency components?  You don't generally bother by those funny noise when you listen to the sub from the listening position.

-Mikey

[rabpaul]

Its not the sub that is distorting but the loud volume that is causing the ear to here them as distortion. You will also hear distortion if you get very close to your main speakers at your normal listening volume.

[bpape]

Actually, many large diameter drivers are poorly designed in terms of rigidity to diameter.  A good sub up to 90+db should have almost no distortion up close.  Flex of the cone instead of pure pistonic motion will cause what you're hearing. 

Bryan