Thanks for raising this issue , actually your point is correct. I have made this design specially for the guys who like hearing their fav songs during cycling. It's a speaker so i think , it will not block all the surrounding sounds as it happen in case of ear phones so it would not be a problem..

Whoa - I wonder how you avoid not compromising safety

The only change which diffrenciate it from conventional helmet is it's sliding features whereas all the other features like safety features would be same as normal helmet. So,I don't think their would be any compromise in the safety ,even if it occurs it would be very less. Also, sometimes you have to lose something good to get something better :)