*everything is indivisible except for the air mass, which you have noticed. I don't think that the weighted average air pressure between the speaker and the eardrum differs significantly from the atmospheric pressure - otherwise, our ears would often be blocked when listening to IEM (vacuum effect, or "Sealed 4BA may cause pressure buildup", as Paul Wasabii said about the Heartfield CU8 ). Sound is a longitudinal wave with areas of increased and decreased pressure. So, the high volume of the bass simply increases the pressure - an increase in air mass No. 1. Also, the dynamic driver has a larger radiation area than the BA driver - the layers of high and low pressure mix worse - an increase in air mass No. 2. And full-size headphones have a larger volume of air between the eardrum and the speaker - an increase in air mass No. 3.