Many otolaryngology textbooks describe the middle ear as an impedance-matching structure designed to offset the 30-dB loss that occurs when sound passes from the low-impedance air of the ear canal to the high-impedance cochlear perilymph. It performs this acoustic function primarily due to the 17:1 ratio between the "effective area" of the tympanic membrane (TM) and the stapes footplate, with a little help from the 1.3:1 malleus handle/long process of incus lever ratio; theoretically, they restore about 27 dB of the 30-dB loss.
This description is not quite correct for the following reasons: (1) the impedance mismatch between air and cochlea is closer to 40 dB between 500 and 4000 Hz, decreasing with increasing frequency1; and (2) the effective area of the TM is not a constant but decreases rapidly above 2000 Hz.2 Since the cochlear input impedance is thought to remain relatively constant between 500 and 4000
GOODE RL. Middle Ear Function, Biologic Variation, and Otosurgical Alchemy: Can We Turn Tin Ears Into Gold? Arch Otolaryngol Head Neck Surg. 1986;112(9):923–924. doi:10.1001/archotol.1986.03780090019001
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