Conventionally, we are able to hear sounds due to tiny vibrations traveling through the air, which are then picked up by our inner ear. However, sound is also able to travel effectively through other materials, such as steel, plastics and even water. Some frequencies are actually able to transfer quite well in solid materials - think of being able to hear a train in the distance by putting your ear to the track (but not for too long!). With Domio, we took the same idea and applied it to the helmet. The helmet is often constructed with a rigid outer shell usually with a plastic such as polycarbonate and a inner shell such as an expanded polystyrene foam. Each material has various properties, such as speed of sound and acoustic impedance, that determine how sound travels through it. It turns out the materials in plastics have actually pretty good baseline properties and can conduct sound quite well. Because the helmet has a concave shape and is fit quite snugly, the sound is then able to enter the user’s ears through two paths: i) through the helmet and then head itself by traveling through the skull and ii) through the surrounding air and into the inner ear as conventional sound works. So the user is able to hear through multiple paths. One big advantage of this is that if the user wishes to use earplugs to protect from a loud environment (think straight pipes on a highway), they can still hear sound with the Domio Pro as it travels through the first path (helmet and head).