will the speakers that come with a Bluetooth headset fit inside a normal helmet or do you need a helmet designed to fit the speakers.
I fitted some in my Arai and they're fine. The speakers are very flat. The only issue was getting them in just the right place so they weren't pushing against the edge of my ears.
I have speakers in my Schuberth C3 Pro and and my Shoei RF1200, bob. I use a Sena with the stock speakers. The speakers work fine but as Octoberon said you have to fiddle a bit to get them adjusted for your ears. I think these days most “normal“ helmets come with speaker pockets. Or at least a place/space where you can affix speakers.
I found a few years back when fitting into my Shoei that did not have recesses that it hurt my ears when doing long distances. Have since changed to a different Shoei with recesses and no issue. I guess it depends on how snug your helmet is?
