Physics of the ear

Hearing and intensity level

The outer ear collects sound; the eardrum and ossicles (middle ear) transmit it to the oval window, increasing the pressure about 20 times; the cochlea converts vibrations into nerve signals. Hearing is roughly logarithmic, so loudness is measured by intensity level $=10\log\frac I{I_0}$ dB, with $I_0=1.0\times10^{-12}$ W m⁻². The dBA scale weights frequencies to match the ear's response.