![]() ![]() Due to a mechanical advantage, the displacements of the stirrup are greater than that of the hammer. The three tiny bones of the middle ear act as levers to amplify the vibrations of the sound wave. The stirrup is connected to the inner ear and thus the vibrations of the stirrup are transmitted to the fluid of the inner ear and create a compression wave within the fluid. As shown below, a compression forces the eardrum inward and a rarefaction forces the eardrum outward, thus vibrating the eardrum at the same frequency of the sound wave.īeing connected to the hammer, the movements of the eardrum will set the hammer, anvil, and stirrup into motion at the same frequency of the sound wave. The eardrum is a very durable and tightly stretched membrane that vibrates as the incoming pressure waves reach it. The middle ear is an air-filled cavity that consists of an eardrum and three tiny, interconnected bones - the hammer, anvil, and stirrup. It is not until the sound reaches the eardrum at the interface of the outer and the middle ear that the energy of the mechanical wave becomes converted into vibrations of the inner bone structure of the ear. As sound travels through the outer ear, the sound is still in the form of a pressure wave, with an alternating pattern of high and low pressure regions. Because of the length of the ear canal, it is capable of amplifying sounds with frequencies of approximately 3000 Hz. The outer ear also channels sound waves that reach the ear through the ear canal to the eardrum of the middle ear. The earflap provides protection for the middle ear in order to prevent damage to the eardrum. ![]() The outer ear consists of an earflap and an approximately 2-cm long ear canal. The three parts of the ear are shown below. The inner ear serves to transform the energy of a compressional wave within the inner ear fluid into nerve impulses that can be transmitted to the brain. The middle ear serves to transform the energy of a sound wave into the internal vibrations of the bone structure of the middle ear and ultimately transform these vibrations into a compressional wave in the inner ear. The outer ear serves to collect and channel sound to the middle ear. Each part of the ear serves a specific purpose in the task of detecting and interpreting sound. The ear consists of three basic parts - the outer ear, the middle ear, and the inner ear. The ear's ability to do this allows us to perceive the pitch of sounds by detection of the wave's frequencies, the loudness of sound by detection of the wave's amplitude and the timbre of the sound by the detection of the various frequencies that make up a complex sound wave. We will attempt to understand how the human ear serves as an astounding transducer, converting sound energy to mechanical energy to a nerve impulse that is transmitted to the brain. In this part of Lesson 2, we will focus on the acoustics (the branch of physics pertaining to sound) of hearing. Understanding how humans hear is a complex subject involving the fields of physiology, psychology and acoustics.
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