Cochlear damage induced tinnitus results mostly from exposure to noise.
Actually give you some insight into what actually happens when cochlea damage occurs as a result of exposure to noise.
There are some of the fifteen thousand microscopic sensory hair cells in the the Organ of Corti which are very fragile and are easily damaged. There are three tiny bones that vibrate and act as amplifiers, in fact probably the beat amplifiers ever invented.
If you look at the illustration shown you will get a better idea of what I am talking about.
When the movement of the tiny bones in the middle ear vibrate the oval window of the cochlea, waves are created in the fluid surrounding the cochlea.
These waves bend the basilar membrane in place corresponding to specific frequencies.
Hair cells in those places then brush against the overlying tectorial membrane (shown in blue) generating an electrical impulse which gets sent to the brain.The brain interprets those electrical impulses as sound. The nerve endings are shown in yellow in the illustration.
When the tiny hairs and nerve endings become damaged as a result of exposure to noise, high frequency hearing loss and tinnitus often results.