The sensation we call sound is produced primarily by variations in air pressure that are detected by their mechanical effect on the tympana (ear drums) of our auditory system. Motion of each tympanum is communicated through a linked triplet of small bones to the fluid inside a spiral cavity, the cochlea, where it induces nerve impulses from sensory hair cells in contact with a thin membrane (the basilar membrane). Any discussion of details of the physiology and psychophysics of the hearing process (Stevens and Davis, 1938; Gulick, 1971) would take us too far afield here. The important point is the dominance of air pressure variation in the mechanism of the hearing process. Direct communication of vibration through the bones of the head to the cochlea is possible, if the vibrating object is in direct contact with the head, and intense vibrations at low frequencies can be felt by nerve transducers in other parts of the body, for example in the case of low organ notes, but this is not part of the primary sense of hearing.
KeywordsTransmission Coefficient Sound Wave Sound Pressure Level Acoustic Pressure Basilar Membrane
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