Due to its shape and wearing position, invisible hearing aids have more advantages in acoustic characteristics than in other types of hearing aids.
1, Helmholtz resonance effect
Marshall believes that because the auricle has the function of reflecting and refracting sound waves, the sound pressure increases between 4000 and 5000Hz when entering the ear canal, and there is resonance of 6~8dB, that is, the sound is in the range of 4000~5000Hz. There is an amplification before entering the microphone. The invisible hearing aid is located deep in the ear canal and does not affect the resonance function of the ear cavity. Since the resonance frequency of the ear cavity is 4000~5000Hz, the maximum peak of the microphone gain of the invisible hearing aid is above 5000hz, and the compensation effect for the high frequency is better, so the high frequency hearing aid effect can be enhanced.
2, mirror effect
The mirror effect is the auricle effect. The high-frequency sound has a shorter wavelength, and the auricle can increase the gain of the high-frequency part of the sound, while the low-frequency sound has a longer wavelength, and the auricle as a reflecting surface (mirror surface) attenuates the low-frequency sound. For a sound larger than 2000Hz, the auricle increases in gain as the frequency increases. However, the auricle effect is related to its measurement point. If measured at the microphone of the in-ear hearing aid, this effect is small; if measured at the microphone position of the invisible hearing aid, this effect is obvious. In addition to the effects of the auricle and the ear canal on the frequency, the high-frequency information of the invisible hearing aid is also affected by the Helmholtz resonance effect associated with the auricle. Ear canal hearing aids are also slightly affected. Unlike the Helmholtz resonance effect, the specular effect is first related to the microphone position of the hearing aid, and this phenomenon is very stable. The size of the auricle plays only a minor role.
3, balloon effect
The balloon effect, Boyle’s law, shows the relationship between pressure and volume: a decrease in volume leads to an increase in pressure.Invisible hearing aidLocated in the deep part of the ear canal, resulting in a decrease in the volume of the external auditory canal. According to the inverse relationship between the volume and the pressure, the volume reduction pressure increases. According to Marshall, the low-frequency output of the invisible hearing aid at the tympanic membrane is 5dB higher and the high-frequency output is higher than 10~17dB compared to the same power ear canal hearing aid.
4, reducing the plugging effect
The invisible hearing aid is located deep in the ear canal, mainly the external auditory canal. When the patient makes a sound, the sound waves generated by the resonance of the cartilage of the external auditory canal wall are leaked, and the vibration of the bone is less generated by the vibration of the bone, so that the ear plugging effect can be reduced.
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