Dr. N.L. Kachhara
An object produces sound when it vibrates in matter. The vibrating object sends a wave of pressure fluctuation through the atmosphere. Sound waves approaching the ear enter either directly or are reflected by the pinna down the auditory canal (meatus) and are conducted to the cochlea by the three ossicles. Sound waves travel through the ear canal to the ear drum (tympanic membrane). The auditory can resonate and amplify sounds within a frequency range of about 2000 Hz to 5500 Hz up to a factor of 10.
Successive compressions and rarefactions of air reaching the ear drum causes the ear drum to vibrate. The vibrations travel to cochlea through three small bones. The bones act as interlocking levers, which amplify the force of the eardrum. This causes a further amplification of the sound vibration, up to 20 times at some frequencies. The hair-like structures (dendrites) in the cochlea resonate at various different frequencies. The vibrations stimulate neurons to produce electrical impulses, which are sent along the auditory nerve to the brain for processing. The brain is able to detect the relative direction of a sound and is also able to perceive the relative distance of a sound source.
The ear can hear sounds form 20 Hz to 20000 Hz. It is most sensitive to frequencies between 500 Hz and 4000 Hz, which corresponds almost exactly to the speech band. Human pressure perceptions range from 20 micro pascal to 200 pascal. Loudness is a subjective term describing the strength of the ear's perception of a sound. It is intimately related to sound intensity. Decibel is a relative measure and is used to quantify both pressure and intensity levels.
