The speakers have a diameter of 40 mm and are approx. 7 mm high Mounted in the following helmets: Shoei GT-Air, X-Lite 1005 Ultra Carbon, Shark Evo One 2, Nolan N80-8. The sound quality is better than HD quality, bass is significantly deeper, volume is fine. Sufficient for phone calls on motorway journeys (keeping the legal speed).
Exciting I briefly measured my earphones and came up with ~4.5cm There is still foam around the earphones, so the measurement may differ in the millimetre range. For me, they don't fit into the bulge in the helmet because of a few millimetres, but they work wonderfully and I don't feel them when I wear them.