J-pipe, or j-bend exhaust

[CFster]

Does anyone have any experience with this? Apparently a j-shaped pipe coming off the exhaust with a capped end reduces drone significantly. Exhaust can't travel into the pipe, because there's no exit, but sound waves will. Once they hit the cap they're bounced back in an inverse sound wave to the original, thus canceling each other out.

I believe location, and the length of the pipe has to be specific.