HIS 140 - Loudness and the Cochlear Amplifier

Loudness & the Cochlear Amplifier

When the basilar membrane and all of the hair cells within the organ of Corti are healthy, the cochlea may be considered a sixty decibel compressor amplifier.


This “amplification” resembles a compression channel in a digital hearing instrument. For example, when increased sound pressure is received, the compressor reduces its amplification performance.


As the outer hair cells within the Organ of Corti become damaged, the cochlear amplifier losses its ability to amplify.


The compressor becomes more linear as more outer hair cells are missing. By the time a sixty decibel sensorineural loss is revealed only inner hair cells remain.


The basilar membrane

The inner and outer hair cells are arranged along the basilar membrane such that pitch (frequencies) are perceived in a specific place within a certain area of the basilar membrane.



The are twenty-four filter bands along the basilar membrane. A pure tone signal (the most discreet sound we can provide) creates a wide excitation pattern upon a specific area of these twenty-four filter bands.



The high frequencies are located along the portion of the basilar membrane closest to the oval window. Let’s reference the placement of all commonly tested pure tones along the basilar membrane.

(Ref. Vonlanthen page # 103)


The Basilar Membrane

As may be noted, if more than one pure tone frequency is present i.e. broadband sound, the more hair cells will be stimulated resulting in an increase of cochlear amplification.


The Basilar Membrane

If outer hair cells become damaged or missing, frequency resolution is removed as well as cochlear amplification.


“Loud but not clear”

When the number of hair cells providing high frequency resolution have been reduced, an abnormal growth of loudness is perceived due to the low frequency hair cells continuing to provide a sensation of loudness through the cochlear amplifier of basilar membrane movement.


Loudness Perception

The perception of loudness is very dependant upon the amount of frequency bandwidth presented to the ear. Discreet amplification resolution can of often be of benefit for those with cochlear hearing loss.

HIS 140 - Loudness and the Cochlear Amplifier

Health & Medicine

perception of loudness

cochlear amplifieras

outer hair cells

basilar membranesuch

ofthe hair cells

onlyinner hair cells

abnormal growth of loudness

hair cellswill