Complete ear canal hearing aid (CIC hearing aids)

Complete ear canal hearing aid (CIC hearing aids)

Complete ear canal hearing aid refers to the shape of the patient according to the shape of the patient;: The external ear canal population, a type of hearing aid that stops near the second curve.
3.6.1 Acoustic characteristics of complete hearing aids

Complete-in-the-cana1, c: Acoustic characteristics of basket baskets. 3-12 ’and the acoustic characteristics
Similar to the device, in addition to the acoustic characteristics of ear canal hearing aids, there are some other acoustic characteristics of the earphone.
Figure 3-12 Complete hearing aid
1. Helmholtz resonance effect
Marshall believes 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 to 5000 Hz, and there is a resonance of 6 to 8 dB, that is, the sound is in the range of 4000 to 5000 Hz. There was amplification before entering the microphone. Complete ear canal hearing aids are located deep in the ear canal and do not affect the resonance function of the ear cavity. Because the resonance frequency of the ear nail cavity is in the range of 4000 to 5000 Hz, and the frequency of the highest peak sound gain at the microphone of a complete ear canal hearing aid is 4700 to 5600 Hz, the high-frequency hearing aid effect can be enhanced.
2. Specular effect
The specular 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 serves as a reflective surface (mirror) to attenuate the low-frequency sound. For sounds greater than 2000 Hz, the auricle increases its gain as the frequency increases. However, the auricle effect is related to its measurement point. If measured at the microphone of an in-ear hearing aid, this effect is very small; if measured at the microphone position of a complete in-ear hearing aid, this effect is obvious, as shown in the figure 3-13.

In addition to the influence of the auricle and ear canal on frequency, high-frequency information of a complete ear canal hearing aid is also affected by the Helmholtz resonance effect associated with the auricle. Hearing aids are also slightly affected.
Unlike the Helmholtz resonance effect, the mirror effect is primarily related to the microphone position of the hearing aid, and this phenomenon is very stable. The size of the pinna plays only a minor role.

3． Balloon effect

Full ear canal hearing aids are located deep in the ear canal, resulting in a reduction in the volume of the external ear canal. According to the inverse relationship between volume and pressure, it can be known that the volume decreases and the pressure increases. Marshall believes that compared with the ear canal hearing aid of the same power, the complete ear canal hearing aid at the eardrum has a low frequency output of 4dB and a high frequency output of 8-15dB. In the case of a hard-walled cavity, the increase in sound pressure is independent of frequency. This does not apply if the impedance of the eardrum is small.
4． Reduce ear plugging effect
Complete ear canal hearing aids are located deep in the ear canal, mainly the outer ear canal bone. When the patient makes a sound, it causes the cartilage of the external auditory meatus wall to leak out the sound waves generated by the vibration, and the sound waves generated by the bone vibration are less, so the occlusion effect can be reduced.
3.6.2 Benefits of Full Ear Canal Hearing Aid
1. Good hearing aid
The acoustic characteristics of the complete ear canal hearing aid determine that it has different acoustic effects from other types of hearing aids, mainly in the following five aspects:

① Improve the sound gain, especially the high frequency sound gain. First of all, since the ear canal hearing aid is located deep in the ear canal, it does not affect the resonance function of the ear cavity. The sound pressure of the external sound at the microphone position is pre-amplified, especially to enhance the hearing aid effect of high-frequency sound. Secondly, the complete ear canal hearing aid is located deep in the ear canal, the volume of the external ear canal decreases, and the sound pressure at the tympanic membrane increases, especially the high output. Thirdly, the complete ear canal hearing aid shortens the length of the external auditory canal more significantly, causing the formant frequency to move forward, and the sound at about 2000 Hz is put at about 10 dB, which acts on the tympanic membrane and significantly improves the hearing resolution. Finally, increase headroom. The so-called headroom refers to the difference between the actual gain and the maximum gain of the hearing aid. Because the full ear canal hearing aid is located in the deep ear canal and the sound outlet is close to the eardrum, the actual gain of the full ear canal hearing aid can be relatively reduced, which results in an increase in headroom and can improve the sound quality of the hearing aid.

② Reduce ear plugging effect. As mentioned before.
③ Improve sound source localization. Normal auricles play an important role in sound source localization. Complete ear canal hearing aids are located deep in the ear canal, retaining the normal auricle shape, and therefore help locate the sound source.
④ High fidelity. Because the distance between the hearing hole of the hearing aid and the eardrum is shortened, the amplified sound acts more directly on the eardrum, so noise and distortion can be better controlled.
⑤ Reduce the requirement for gain. Complete ear canal hearing aids can increase sound gain, increase output, increase headroom, reduce ear plugging effects, etc., so their requirements for gain will be reduced.

2. Small size and strong concealment
In-ear and in-ear hearing aids are located approximately 1/3 of the outer ear canal and in the ear cavity respectively, while complete in-ear hearing aids are located deep in the ear canal, are only the size of small nails, are concealed and difficult to be found, which can meet the greatest deafness Human aesthetic and psychological needs.
3． Comfortable and fixed
The complete ear canal hearing aid can be customized according to the shape of the patient’s ear canal (in-ear also includes the ear cavity). Because the shape of the hearing aid matches the anatomical structure of the patient’s external ear canal, the shape is small, comfortable to wear and not easy to fall off.
4． Less chance of injury
Because the hearing aid is located deeper, it is less affected by sweat and dust, so there is less chance of accidental damage.

3.6.3 Disadvantages of Full Ear Canal Hearing Aid
Disadvantages of a complete ear canal hearing aid include:
① The size and battery of the complete ear canal hearing aid are small, and the elderly or those with poor flexibility of the hands are inconvenient to operate and easy to lose.
② The output power is limited and it is not suitable for patients with severe hearing impairment.
③ There is evaporation of moisture and oil from the skin in the ear canal. When a complete ear canal hearing aid is placed in the ear canal, the ear canal is blocked.
Evaporated moisture and grease can damage parts inside the hearing aid.
④ The distance between the microphone and the sound hole is relatively short, which is likely to cause acoustic feedback.
⑤Direction and multi-microphone systems cannot be configured, pickup coils cannot be installed, and FM systems cannot be connected.
⑥ Special customization is required, and mass production is not allowed, so the price is more expensive.
Like earphones, tadpoles are not suitable for minors with undeveloped ear canals.
People with constant discharge of middle ear, those who have undergone radical ear surgery or external ear canal deformities should be selected with caution.
Compared to several other types of hearing aids, fully in-canal hearing aids are more expensive.
3.6.4 Adaptation range of complete hearing aids
For patients with hearing loss of less than 80dB, the full range of hearing aids is basically the same as the range of hearing aids