Because of its shape and wearing position, the invisible hearing aid has more advantages in acoustic characteristics than other types of hearing aids except for its invisible appearance.
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1. Helmholtz resonance effect
Marshall thinks that, because the auricle has the function of reflecting and refracting sound waves, when the sound enters the ear canal, the sound pressure increases between 4000-5000hz, and there is 6-8db resonance, that is to say, the sound is in the range of 4000-5000hz, and it is amplified before entering the microphone. The invisible hearing aid is located in the deep part of the ear canal, which does not affect the resonance function of the concha cavity. Because the resonance frequency of the cavity is 4000 ~ 5000Hz, and the maximum gain of the microphone of the invisible hearing aid is above 5000Hz, 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 wavelength of high frequency sound is shorter, the pinna can increase the gain of high frequency part of sound, while the wavelength of low frequency sound is longer, the pinna as a reflecting surface (mirror) attenuates low frequency sound. The auricle gain increases with the increase of frequency for the sound greater than 2000 Hz. However, the auricle effect is related to its measuring point. If it is measured at the microphone of the in ear hearing aid, the effect is very small; if it is measured at the microphone position of the invisible hearing aid, the effect is very obvious. In addition to the influence of auricle and auditory canal on frequency, the high frequency information of the hearing aid is also affected by the Helmholtz resonance effect related to auricle. Ear canal hearing aids are also slightly affected. Unlike the Helmholtz resonance effect, the mirror effect is first related to the microphone position of the hearing aid, and this phenomenon is very stable. The size of the auricle only plays a minor role.
3. Balloon effect
The balloon effect, Boyle’s law, shows the relationship between pressure and volume: the decrease of volume will lead to the increase of pressure. < a href = "http://www.sqhearing.com/tlkp/3.html" target = "blank" > the invisible hearing aid < / a > is located in the deep part of the ear canal, resulting in the reduction of the volume of the external auditory canal. According to the inverse relationship between volume and pressure, volume decreases and pressure increases. Marshall thinks that compared with the same power ear canal hearing aid, the low-frequency output of the invisible hearing aid at the tympanic membrane is 5dB higher, and the high-frequency output is 10-17db higher.
4. Reduce ear blocking effect
The invisible hearing aid is located in the deep part of the auditory canal, mainly the bone part of the external auditory canal. When the patient makes a sound, the sound wave produced by the resonance of cartilage part of the external auditory canal wall is released, while the sound wave produced by the vibration of bone part is less, so the ear blocking effect can be reduced.
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Link：Advantages of invisible hearing aids
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