going against the tide of the senior members, but...
night & day, arctic & desert, no comparison whatsoever, none!
went to my local Cycle Gear shop and told them what was going on. they said give this helmet a try, so i did. night & day, arctic & desert, no comparison whatsoever, none! easily scores of decibels quieter (no idea how to measure decibels, but you get the idea). i might still play around a bit more wioth some of the other ideas put forth here, but i can't expect things to get too much quieter than it is now.
old helmet - Biltwell Gringo
new helmet - Shoei RF1200
i can easily put a sound system in this helmet.