I bought two of the NACA 2" ducts after reading this post and the endless posts in the GS list (love those guys) and after a short ride today I can say that it works. I'd tried a few things to stop the awful vibration I got with the Arai XD visor all to no avail. This did it. It's quiet - at least up to 80-90 or so but for average cruising it's smooth air. I'll put up some photos tomorrow.