Thought I would share a little hack that has been serving me well.
I wanted some bluetooth speakers for my full face helmet, but also didn't want to spend hundreds of dollars on what would without a doubt end up to be a mediocre audio experience because... well... you're riding a vespa and trying to listen to audio in a helmet... not the most pristine conditions.
Anyway, I ended up buying a pair of these wireless Koss headphones ( https://a.co/d/ieHcjF4 ) because it looked like it would fit the 40mm cut out in my helmet, and sure enough they did. Had to cut off the ear clip part, threw some velcro behind the headphone to adhere it to the inside of the helmet cut out, tucked wiring in behind pads, and I got a pretty good sounding setup. Took a little while to position the speakers just right, but was worth it in the end. Can't take calls or anything on it, but I don't want to do that anyway
Do with this what you will! Inexpensive way to get some music in your helmet.