Amplification of sound pressure by the tympanic membrane

The first point: the leverage of the curved periosteum

HelmholtzIt was the earliest hypothesis that the curved tympanic membrane was leveraged. He believes that the vibration amplitude of some parts of the tympanic membrane is larger than the vibration amplitude of the hammer stem. The arc vibration mode of the tympanic membrane produces a new lever mechanism. The curved tympanic membrane causes the tympanic membrane to move longer than the hammer shank. According to the principle of leverage, the hammer shank The force on the upper surface should be greater than the force exerted on the entire surface of the tympanic membrane, and the sound pressure reaching the tympanic membrane is amplified when it is transmitted to the ossicular chain. According to research, the curved tympanic membrane lever mechanism can provide sound pressure in the middle ear of the cat. improve2Times.

The second point: the area of ​​the tympanic membrane pressurization effect

The area boost effect of the tympanic membrane is one of the most important aspects of the impedance matching of the middle ear. The vibrational force of the sound wave acting on the tympanic membrane should be equal to the force acting on the vestibular window. However, since the area of ​​the tympanic membrane greatly exceeds the area of ​​the humeral footplate, the pressure acting on the unit area of ​​the humerus footplate greatly exceeds the effect and the tympanic membrane. The pressure on it.