Sound amplified with the full and 3/4 helmet. The shape of a full face helmet is somewhat of a bell shape. This shape is used to vibrate and send out sound. It would only be reasonable that objects like a helmet with an open bottom would also react in the same way to sound resonating from below it. Thus your head is inside a bell shaped object "or Bell helmet" that picks up vibrations the outer shell and noise below and amplifies it to your ears. Some helmets would transfer sound better than others depending on multiple variables.== padding, fit, material, head shape , helmet shape, muffler choice of decibel and relation to rider location.
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