I just reviewed noise suppressing headsets and ear buds for a work application. Pretty amazing technology. It can suppress background noises in excess of 110db to less than 82db while enhancing speech to about 86db if I remember correctly. You can hear a person talking at normal volume while standing beside a diesel truck running at high idle (96db) with no problem.
BUT, you need to insert the ear buds properly OR you need to wear ear muffs. I don't know how you could work that into a helmet that you simply slide onto your head. I think you'd still need to insert ear buds and you need to do that well.
BTW, it was obvious during the demo that almost nobody inserts earbuds properly.
If someone is interested, the product is made by an Australian company called Sensear. Pretty cool stuff but not cheap.
2010 BMW S1000RR