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September 1986

Middle Ear Function, Biologic Variation, and Otosurgical Alchemy: Can We Turn Tin Ears Into Gold?

Author Affiliations

Stanford, Calif

Arch Otolaryngol Head Neck Surg. 1986;112(9):923-924. doi:10.1001/archotol.1986.03780090019001

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