Concentric means one circle within another...I would assume that the two knobs would operate independently, although I've never seen one myself, and don't know what they would look like (with the knobs on, that is).

However, come to think of it, you can find a dual concentric pot/knob on the Boss MT-2; for the high/low knob and the mid/mid freq knob. If you have one or ever see one, you'll know what I mean.

OK, I'll post a pic for you.



Here's the link

Google is your friend...