I did a nice ride today, 350km on beautiful roads.
I have a Givi windshield, a HJC CL-15 helmet, I'm 6 feet tall.
The windshield I mounted 2 holes higher with 2 plates and the OEM windshield is on the lower part, up side down.
I saw a great improvement in noise reduction when I switched from OEM to the current setup and I said that this must be the best I can do with the noise, I have speakers in my helmet and I can hear music up to 130km/h. The noise is not uniform, it comes from the windshield and hits my helmet about the visor level.
I tried something today: going 90 km/h, I moved forward and put my lower part of the helmet to touch the windshield. The helmet was above the windshield. And the noise completely disappeared...I could hear the engine running very nice, I could hear a part of the air flowing around the helmet, but not that buffeting noise coming from the windshield....
Now my mind looks for a solution... how about mounting a windshield on the chest and remove the windshield from the front end?
I always thought that the helmet is the problem... now I'm not so sure...