ITE hearing aid

The basic structure of the in-the-ear type and the ITE hearing aid are similar, and they are composed of a housing, a microphone, an integrated circuit amplifier, a potentiometer, and a receiver (see Figure 3-10).

1.shell

Both ITE hearing aid and in ear canal hearing aids are a shell customized according to the shape of the patient's ear canal (in-ear also includes the ear cavity), and the hearing aid movement is housed in the shell. The material of the casing is required to be non-toxic, not cause allergic reactions, stable, not easily affected by temperature, etc., not easy to age and has a smooth surface without impurities.

The earphone-type hearing aid housing of the analog line is also equipped with a volume regulator, a tone adjustment file, a maximum sound output adjustment file, and the like, and some programmable ITE hearing aid or in ear canal hearing aids are also equipped with program switching buttons. In addition, some hearing aids are also equipped with a pull cord on the outer side, and a sound baffle is also installed on the sound outlet.

2.microphone

Figure: ITE hearing aid

1-Volume control potentiometer
2-Microphone
3-Amplifier
4-Trimmer potentiometer
5-Shell
6-Receiver

Figure: Structure of ITE hearing aid and in ear canal hearing aids

Due to the larger form of ITE hearing aid and in ear canal hearing aids, dual microphones can be installed. Full ear canal hearing aids are difficult to install with dual microphones.

3.Integrated circuit amplifier

Due to the miniaturization of electronic components and increased electronic integration, integrated circuit amplifiers for hearing aids are becoming more sophisticated. In particular, digital signal processing is applied, which can add many functions without adding additional components and occupy the limited space of the hearing aid. This provides the conditions for making smaller and better fully in-canal hearing aids.

4.battery

ITE hearing aid uses A13 batteries, in ear canal hearing aids use A312 batteries, and full-in-ear hearing aids use A10 or even A5 batteries.

1.Changes in Formal Frequency of the External Ear Canal

The resonance frequency of the adult external auditory canal is about 2000 to 4000 Hz. The theoretical average is 3359 Hz for males and 3440 Hz for females. The adult external ear resonance frequency measured by Bu Xingkuan is (2583 ± 323) Hz, and the peak gain effect of the external ear canal resonance frequency at 2500 Hz can reach 11-12dB.

When the patient wears an ITE hearing aid, the frequency of the highest peak value of the sound gain at the microphone is at 5118 ~ 5638Hz, indicating that the ITE hearing aid still has a specific effect on the ear canal formant shift, but it is maintained at the average human ear canal form. Frequency position, plus their ability to compensate for high frequencies. Therefore, wearing such ITE hearing aid can improve the patient's speech intelligibility.

2.The frequency response curve of ITE hearing aid

The highest peak of the frequency response curve of an ITE hearing aidis about 2500-2700Hz, which is close to the resonance peak of the external ear canal in a normal person. Gao Jianlin and others believe that the frequency range of the frequency response curve of ITE hearing aid is about 200 ~ 7500Hz, and the frequency range is wide, which almost covers the language area of the human ear. The frequency response curve fluctuates slightly, and the curve is relatively smooth, which aligns with the human ear. The auditory response is similar, so it can enhance hearing effects.

Gao Jianlin's experiments show that the hearing compensation at 1000Hz, 2000Hz, and 4000Hz for ITE hearing aid and in ear canal hearing aids is 25-33dB, while the hearing compensation at 250-500Hz is 20-24dB. The former's hearing compensation ability is greater than the latter.

3. Sound gain at the microphone position

There are many rolls on the outer side of the auricle of a person, which form the same group of concave mirrors. They can reflect and refract the sound coming from the outside world, thereby increasing the sound pressure of the sound coming from the outside world at the microphone position. Compared with behind-the-ear hearing aids, the microphone of the ITE hearing aid is located in the ear, and this principle enhances its hearing aid effect. The anatomical positions of the ear nails and/or the external ear canal occupied by the in-the-ear and  ITE hearing aid are different, and the microphone positions of different types of ITE hearing aid are different, so their sound gains are also different. Gao Jianlin also found in the experiment that the sound gain at the microphone of the ITE hearing aid is 5.94 to 6.46dB SPL, with an average of (6. 29 ± 1.09) dB SPL; the ITE hearing aid is 6.90-9. The average is (8. 08 ± 1.83) dB SPL; the complete ear canal hearing aid is 8. 80 ～ 9. 30dB SPL, and the average is (9. 01 ± 1.73) dB SPL. There are significant differences between the three.

The sound gain at the microphone position of the full ear canal hearing aid is the largest, followed by the in ear canal hearing aids and the ITE hearing aid. Since this value is obtained when the hearing aid is not output, the sound gain at the microphone position is related to the anatomy, physiological characteristics of the auricle, and the style of the hearing aid, and has nothing to do with the power of the hearing aid.

The advantages of  ITE hearing aid compared to in-ear and full-ear hearing aids are:

• The range suitable for hearing loss is wide, and the output power is significant.
• Can easily install additional components, such as dual microphones, pickup coils.
• It is easier to replace the battery and adjust the volume than the in ear canal hearing aidsand completely in canal hearing aids.

Disadvantages of ITE hearing aid include:

• Because a child's ear canal is not developed and shaped, the shell needs to be replaced regularly, so it is not suitable for use.
• Compared with the behind-the-ear hearing aid, the ITE hearing aidmicrophone is closer to the receiver's outlet, and it is easier to generate acoustic feedback.
• For older peopleand those with less flexible hands, changing the battery and adjusting the volume is not convenient.
• Although it is located in the ear, the ITE hearing aid’sshape is still too large, and it is easier to see.
• Cerumen is easy to enter the hearing aid through the sound hole,damaging the internal movement.
• The ear nail cavity hearing aid fills the entire ear nail cavity, and some patients may feel uncomfortable because too much skin is closed.
• As with the BTE hearing aids mentioned earlier, ear plugging can easily occur.

The power range of the ITE hearing aid is generally 40 to 110 dB. Combining its acoustic characteristics and advantages and disadvantages, ITE hearing aid is usually suitable for patients with moderate to severe hearing loss but are unwilling to wear behind-the-ear hearing aids. In addition, because ITE hearing aid can easily install more auxiliary parts, they are more suitable for hearing aid performance High patients; for middle-aged and older people or patients with flexible hands and severe hearing loss, you can also consider the option of ITE hearing aid.

ITE hearing aid

In ear canal hearing aids refer to a type of hearing aid that is customized to the patient's external auditory canal and starts in the ear cavity, and stops near the second curve.

Classification of hearing aids

In ear canal (ITC) hearing aids (Figure 3-11) are also custom-made hearing aids. Unlike ITE hearing aid,  ITE hearing aid is located in the patient's ear canal. According to the size, ear canal hearing aids can be further divided into the ear canal (ITC), small ear canal (small ITC or mini-canal), and complete ear canal (CIC) three types of hearing aids. Completely in canal hearing aids have two standards. Only when these two standards are met can they be called completely in canal hearing aids, and the best gain and output can be obtained. First, the side part of the ear canal hearing aid shown in Figure 3-11 should be at least close to the outer ear canal or 1 to 2 mm inside the ear canal; second, the medial part should be within 5 mm from the upper part of the eardrum.

If a completely in canal hearing aids fail to achieve the above two points, it can only obtain the advantages of a partial complete ear canal, and it can only be called a small ear canal hearing aid. The ear canal hearing aid is also located in the ear canal, but it is slightly larger than the full ear canal and small ear canal hearing aids.

The ear canal hearing aid not only has the aforementioned acoustic characteristics of the ITE hearing aid, but also accords with the physiological acoustic characteristics of the human ear, and its hearing enhancement effect is better.

1.Changes in Formal Mouth Frequencies

When a patient wears an ear canal hearing aid, the frequency of the highest peak value of the sound gain at the microphone is 4733-5179 Hz, which is closer to the frequency position of the resonance peak of the external ear canal in ordinary people.

2.Changes in resonance effect after ear canal obstruction

The external auditory meatus is a hollow blind box. According to acoustic theory, a closed box has a resonance amplification effect on the sound waves 4 times the length of the box. For example, the length of the tube is 2.5 cm, and the acoustic wavelength of the resonance frequency is 10 cm, according to the speed of 344 m. / s calculation, the resonance frequency is 3440Hz. The air column in the tube resonates with the sound wave of this frequency so that the sound pressure of the sound at the frequency at the blind end of the tube increases.

The in ear canal hearing aids "blocks the tube" of the external auditory canal, shorten the external auditory canal's length, and move the formant frequency forward. In this case, the sound information of the speech frequency is effectively amplified, so that the auditory resolution is significantly improved.

3.Aura-preserving resonance effect and sound source localization

The main physiological function of the auricle is to orient, locate, collect, and amplify external sounds. The normal auricle has the function of collecting sound, and the uneven structure on the surface of the auricle produces different reflections on sound sources from different orientations and heights, and has a resonance amplification effect on sound of a certain frequency. This function of the auricle can produce a filtering effect, which plays an important role in sound source localization. The in ear canal hearing aids is located in the ear canal and retain more of the standard structure of the auricle, so it helps to naturally amplify the sound and locate the sound source.

4.Effect of sound hole close to eardrum on sound gain

First, because the distance between the hearing hole of the hearing aid and the eardrum is shortened, the amplified sound can directly act on the eardrum, so the distortion is minor. Second, the in ear canal hearing aids are placed 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, volume decreases and pressure increases. Therefore, when wearing an in ear canal hearing aids, its sound pressure will increase.

Compared with behind-the-ear and in-the-ear hearing aids, the advantages of in ear canal hearing aids include the following,

• The shape is small, which can meet the aesthetic requirements of patients, and is more comfortable to wear.
• Located in the ear canal, it retains the normal structure of the auricle, which is more in line with the physiological and acoustic characteristics of the human ear. Ithelps to improve sound gain and sound source localization.

Disadvantages of  in ear canal hearing aids include:

• As with in ear canal hearing aids, since the ear canal of a child is not developed and shaped, the shell needs to be replaced regularly, so children should use it with caution.
• The in ear canal hearing aidsare only suitable for patients with mild or moderate hearing loss. At present, the in ear canal hearing aids with the highest power are only suitable for patients with an average hearing threshold of 90 to 95 dB.
• The battery and volume adjuster of thein ear canal hearing aids are smaller than the ITE hearing aid, so it is more challenging to operate.
• As mentioned earlier, due to the smaller internal space, thein ear canal hearing aids are more likely to generate acoustic feedback, and they cannot be connected to the FM system.
• As with  ITE hearing aid, ITE hearing aid is located in the ear canal and are more susceptible to the effects of radon.
• As with  ITE hearing aid, they can also produce ear-plugging effects.

• At present, the power of commonly used ear canal hearing aids is generally below 80 dB, and some brands of some models of high power ear canal hearing aids can reach 90 to 100 dB, but clinical applications are not widespread. Hearing aids are currently commonly used in the following groups:Patients who are younger, have mild to moderate hearing loss, and have higher requirements for hearing aids.
•  Middle-aged and elderly people with mild to moderate hearing loss, flexible hands and high requirements for hearing aid effect and appearance.
• The average hearing loss is below 80-85dB. For patients with a descending hearing curve with low frequency and high frequency hearing loss, the ear canal hearing aid can give more high frequency gain compensation.