When purchasing my ridge I was wondering how well the visor worked and one day I took some readings for future ROCers just prior to taking it off to put on opticoat. I couldn't find the large post I read discussing it but figured posting here would be helpful for others looking in the future. I used the sound meter app and put my phone in the same cradle in the same spot and drove the same section of road circling from one exit to the other. I think consistency would be more important than the meter for reference purposes a long as the meter was decent. I tried to choose the best app naturally. I chose a speed of 70 mph on cruise control for a round number where I wouldn't get a ticket. Below freeway speed seemed very quiet and the AC was louder, but the freeway db surprised me even with the visor on.
Results:
Visor on - cruise on at 70 mph = 69 to a max of 71 db depending on road bumps and wind changes
Visor off - cruise on at 70 mph = 76 to max of 78 db depending on road bumps and wind changes
I couldn't remember the number where sound doubled, After a little research - 10db is twice as loud.
I guess you could complain about the meter, wind change conditions over the half hour, etc, but for lay purposes there is a decrease in noise. Also having the passenger rear window cracked a tiny bit had the lowest noise level reduction by a db or 2.
I cannot remember the db with the AC up all the way and the roof closed, except that the AC was louder than the sunroof open with the visor off.
Hope that helps. Please pardon grammar, this was written on my phone
p.s. In my opinion putting sound dampening material under the carpet on the floor and on doors seemed like a better choice to reduce noise when we were taking readings and discussing overall noise with my wife while doing all of this. Luxury cars are much quieter with that material, at least my wife's is. She helped run the phone and take numbers.