Sound reaches maximum amplitude depending on its frequency at:
Tympanic membrane
Ear ossicles
Semicircular canals
B asilar membrane
Ref: Diseases of Ear, Nose & Throat, by Dhingra 5th edition. Chapter on Physiology of EarExplanation:A sound wave depending on its frequency reaches maximum amplitude on a particular place on hasilar membrane and stimulates that segment.Higher frequencies are represented in the basal turn of cochlea and progressively lower ones towards the apex.
Physiology of Ear