Hearing / Middle ear / Acoustic impedance
Acoustic impedance
 the core concept is that the effectiveness of transmitting vibration is frequency dependent i.e, every object has a resonant frequency, and that frequency is determined by an object's acoustic impedance

we manipulate acoustic impedance when we construct musical instruments

 two properties determine an object's resonant frequency:
 MASS: heavier objects vibrate at a lower frequencies
(i.e., mass limits high frequency transmission) this is the more intuitive concept  think of a xylophone: lower frequencies use bigger keys
 STIFFNESS: less elastic objects vibrate at a higher frequencies
(i.e., stiffness limits low frequency transmission)
think of a flute or recorder: changing the length of an air column changes its elasticity; the shorter the column, the higher the resonant frequency

 MASS: heavier objects vibrate at a lower frequencies
 in the middle ear, the ossicles contribute mass and the volume of the middle ear space affects stiffness
 alterations of middle ear impedance significantly impact hearing because the incredible sensitivity of the cochlea means that any sounds reaching the cochlea can be transduced

two examples where changes in middle ear impedance cause hearing loss are otosclerosis and otitis media
 in the cochlea, the establishment of gradients for mass and stiffness along the basilar membrane are responsible for establishment of the place principle