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General performance of high frequency loss:

Performance 1. I don’t know the voice of others, especially female voices and children’s voices or small voices;

Performance 2. The voice of two or more people cannot be heard clearly;

Performance three, pronunciation, spit is not clear, there is a “big tongue” phenomenon, do not like to talk, do not love to communicate with you;

Performance 4, can not hear the high frequency of key sounds such as bird sounds, insects or telephone ring tones;

Performance 5, listening to the sound is not natural and uncomfortable.

High frequency steep drop hearing loss is most common mainly related to various anatomical parts of the ear.

First take a look at the following cases:

1, the funnel-like structure of the outer ear and the curved “S” ear canal, which changes the acoustic physics of the outside world.

As shown in the above figure, the changes in the sound gain of the human auricle and the ear canal for different frequency segments can be seen: the ear canal has the largest gain in sound at the frequency 2kHz-4kHz. Studies have shown that the noise-induced hearing loss is often located at twice the frequency above the noise frequency, the industrial noise is relatively constant in the low-IF range, and the natural auditory peak of the external auditory canal is 2kHz-4kHz, which is the easiest to cause hearing in the 4kHz-6kHz frequency range. loss. This is why noise deafness initially begins with hearing loss starting around 4KHz, gradually damaging the effect to a better frequency.

2, cochlear spiral structure

The sound is transmitted from the external auditory canal through the ossicular chain to the vestibular window of the inner ear. The shearing motion of the basement membrane suspended in the cochlea causes the change of the hair cell potential on the cerebral cortex.

The cochlear structure resembles a snail with a helical structure, approximately 2.5 circle-2.75 circle. The way in which sound waves propagate on the basement membrane is based on the principle of traveling waves in physics, that is, the traveling wave theory. The maximum amplitude portion of the basement membrane is related to the frequency of the sound wave, that is, the sound wave of each frequency has a corresponding maximum amplitude portion at different positions on the basement membrane: the maximum amplitude portion caused by the high frequency sound is near the vestibular window at the worm bottom, and the maximum amplitude of the low frequency Near the volute, the intermediate frequency resonates in the middle. It can be seen that the transmission path of the sound from high frequency to low frequency requires the vibration of the base film at the bottom, that is, the base film of the high frequency band is relatively easy to fatigue. At the same time, the basement membrane hair cells of the cochlea contain lower antioxidant enzymes than the apical hair cells, so the hearing loss of aminoglycoside antibiotics (gentamicin, kanamycin, streptomycin, etc.) ototoxic drugs is Steep down hearing curve.

3, auditory nerve audio distribution

The distribution of the auditory nerve is in the same vein as the spiral structure of the basement membrane of the cochlea. The nerves that sense the low frequency are located at the center, and the high-frequency auditory nerve is located in the periphery. Changes in physical and chemical environments such as trauma, ischemia, hypoxia, and herpesvirus first affect high frequency.

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