... remarkable in the light of the FIGURE 2. 12 (A) Average displacements of the umbo, the head of the stapes and the lenticular process of the incus (B) The lever ratio at 124 dB SPL at the tympanic ... between the effective area of the tympanic membrane and the area of the stapes footplate, but the lever ratio of the middle ear bones also contributes The ratio of areas of the BOX 2. 2 SOUND ... at the entrance of the ear canal compared with the sound pressure that is measured in the place of the head The effect of the head on the sound at the entrance of the ear canal is related to the...