Noise Induced Or Sensori-Neural Hearing Loss

This form of hearing loss is produced gradually from long term exposure to noise.  Over its years of development, the condition begins by affecting high frequencies (usually at the 4000 hertz level) and eventually those at the lower levels.

Employees suffering from industrial deafness will have reasonably normal low frequency hearing, but distorted high frequency hearing.  The volume of speech is unaffected, yet the clarity of speech, determined by consonants, lessens.

The sound energy range most important for speech is between 1000 to 6000 hertz (Hz).  Accordingly, the most emphasis will be placed on this range.

Because noise induced hearing loss is sensory-neural, affecting the inner ear, air conduction and bone conduction levels will be approximately the same for each frequency.

There is no problem with the signals getting to the cochlea, but there are problems in the conversion of these signals in the inner ear.  Frequency at 4000Hz will be affected first, with a gradual deterioration over time affecting lower frequencies.