Why do high-frequency sounds stimulate the base of the basilar membrane?

High-frequency sounds stimulate the base of the basilar membrane because of the membrane's physical properties, which vary along its length from the base near the oval window to the apex at the tip of the cochlea.12

The basilar membrane is not uniform; it is characterized by a gradient of stiffness and mass. Specifically, the basal end is narrower, has less mass, and possesses greater stiffness compared to the apical end. Because of this structural configuration, the basal region is more attuned to high-frequency vibrations.12

When sound waves enter the cochlea, they create traveling waves along the membrane. High-frequency sounds cause these waves to reach their maximum amplitude at the stiffer, basal end of the membrane before subsiding. This localized peak of vibration stimulates the hair cells in that specific area of the organ of Corti, which then transmit the corresponding signals to the brain to be perceived as high-pitched sounds.12