ITE hearing aid

1. Changes in Formal Frequency of the External Ear Canal

The resonance frequency of the adult external auditory canal is typically between 2000 and 4000 Hz, with theoretical averages of 3359 Hz for males and 3440 Hz for females. Measurements by Bu Xingkuan place the resonance at (2583 ± 323) Hz, with a peak gain around 2500 Hz reaching 11–12 dB.

When wearing an ITE hearing aid, the highest microphone-side peak shifts to roughly 5118–5638 Hz. Although the formant position changes, it still aligns with the natural resonance range of the ear canal and provides additional high-frequency compensation. This explains why an ITE hearing aid can meaningfully improve speech intelligibility.

2. The frequency response curve of ITE hearing aid

The frequency-response peak of an ITE hearing aid is usually around 2500–2700 Hz, close to the normal outer-ear resonance. According to Gao Jianlin, the response range of the ITE hearing aid extends from approximately 200 to 7500 Hz—broad enough to cover the full speech frequency band. The curve remains smooth with minimal fluctuations, aligning well with natural auditory characteristics.

Gao Jianlin's experiments also show that ITE hearing aid and in-ear canal devices provide 25–33 dB of gain at 1000, 2000, and 4000 Hz, and 20–24 dB at 250–500 Hz, with the former offering slightly stronger compensation.

3. Sound gain at the microphone position

The folds of the human auricle act like multiple concave reflectors, increasing sound pressure at the microphone position. Since the microphone of an ITE hearing aid sits inside the ear rather than behind it, this natural acoustic effect enhances performance. Due to differences in ear-canal anatomy and device style, microphone sound gain varies across models. Experiments show microphone gain for ITE hearing aid ranges from 5.94 to 6.46 dB SPL, averaging (6.29 ± 1.09) dB SPL; in-ear canal devices show (8.08 ± 1.83) dB SPL; full canal models reach 8.80–9.30 dB SPL. These differences are structural rather than related to ITE hearing amplifier power output.

The advantages of ITE hearing aid compared to other custom styles include:

• It supports a wide range of hearing loss and offers significant output power.
• It can easily accommodate additional components, such as dual microphones or telecoils.
• Compared to deeper-fitting models like completely-in-canal (CIC) hearing aids, the ITE hearing aid is easier to handle for battery replacement and volume adjustment.

• It is unsuitable for children, as their ear canals are still developing, requiring frequent shell replacement.
• Its microphone is closer to the receiver compared to BTE hearing aids, making it more susceptible to acoustic feedback (whistling).
• For seniors or individuals with limited dexterity, changing batteries and adjusting volume can be challenging.
• While placed in the ear, its shell is relatively larger and more visible than deeper-canal models.
• Cerumen (earwax) can easily enter the device through the sound port, potentially damaging internal components.
• As it fills the concha of the ear, some users may experience a plugged sensation or discomfort due to the occlusion of the ear canal.
• Similar to BTE hearing aids, it can cause a feeling of ear blockage.

The power range of ITE hearing aid is generally 40 to 110 dB. Considering its acoustic characteristics and profile, ITE hearing aid is typically suitable for patients with moderate to severe hearing loss who prefer not to wear BTE hearing aids. Furthermore, as ITE hearing aid can easily integrate more advanced features, they are well-suited for users requiring higher hearing aid performance. For middle-aged or older adults with severe hearing loss and sufficient manual dexterity, ITE hearing aid is also a viable option. Many ite hearing aid manufacturers develop best ite hearing aids and ite rechargeable hearing aids within this category to meet diverse user needs.

ITE Hearing Aids

In-ear-canal hearing aids refer to a type of hearing device custom-made to fit the patient's external auditory canal, extending from the ear cavity to near the second bend.

Classification of Hearing Aids

In-the-canal (ITC) hearing aids are also custom-made devices. Unlike the standard ITE hearing aid which sits in the concha, ITC hearing aids are positioned within the ear canal itself. Based on size, canal hearing aids can be further categorized into in-the-canal (ITC), mini-canal (small ITC), and completely-in-canal (CIC) types. True completely-in-canal hearing aids must meet two specific criteria to be classified as such and to achieve optimal gain and output: First, the lateral face of the aid should be flush with or 1-2 mm inside the ear canal opening; second, the medial part should be within 5 mm of the eardrum. If a device fails to meet these criteria, it may only offer partial benefits of a deep fit and is more accurately termed a mini-canal hearing aid. The standard ITC hearing aid is also located in the ear canal but is slightly larger than both CIC and mini-canal models.

In ear canal hearing aids not only share the acoustic characteristics of ITE hearing aid but also align more closely with the physiological acoustic properties of the human ear, resulting in a superior hearing enhancement effect.

1. Changes in Formant Frequencies

When a patient wears an in ear canal hearing aids, the frequency of the highest peak sound gain at the microphone ranges from 4733 to 5179 Hz. This is closer to the resonant peak frequency of the external ear canal found in individuals with normal hearing.

2. Changes in Resonance Effect After Ear Canal Occlusion

The external auditory canal is a hollow, blind-ended tube. Acoustic theory states that a closed tube resonates with and amplifies sound waves with a wavelength four times its length. For instance, a tube length of 2.5 cm corresponds to a resonant frequency wavelength of 10 cm. Calculating with a sound speed of 344 m/s, the resonant frequency is 3440 Hz. The air column in the tube resonates with sound waves of this frequency, increasing the sound pressure at the closed end.
In ear canal hearing aids occlude the external auditory canal, effectively shortening its length and shifting the formant frequency higher. This effectively amplifies speech frequency information, leading to significantly improved auditory resolution.

3. Aura-Preserving Resonance Effect and Sound Source Localization

The primary physiological functions of the auricle are to orient, locate, collect, and amplify external sounds. The normal auricle collects sound, and its uneven surface structure causes differential reflections of sound sources from various directions and heights, plus a resonant amplification effect for specific frequencies. This filtering capability is crucial for sound source localization. As in ear canal hearing aids are positioned within the ear canal, they preserve more of the auricle's natural structure, thereby aiding in natural sound amplification and sound source localization.

4. Effect of Sound Outlet Proximity to the Eardrum on Sound Gain

Firstly, because the distance between the hearing aid's sound outlet and the eardrum is reduced, the amplified sound acts directly on the eardrum, minimizing distortion. Secondly, the placement of in ear canal hearing aids reduces the volume of the external ear canal cavity. According to the inverse relationship between volume and pressure, a smaller volume results in higher pressure. Consequently, wearing an in ear canal hearing aids increases the sound pressure level at the eardrum.

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

• Their small size meets aesthetic demands and offers greater wearing comfort.
• Positioned inside the ear canal, they preserve the auricle's natural structure, better conforming to human ear physiology and acoustics, which aids in improving sound gain and sound source localization.

1. Similar to ITE hearing aid, they are generally unsuitable for children whose ear canals are still developing and would require frequent shell replacements.
2. They are typically only suitable for mild to moderate hearing loss. Currently, the most powerful in ear canal hearing aidsare only appropriate for an average hearing threshold of 90-95 dB.
3. Their batteries and volume adjusters are smaller than those of ITE hearing aid, making them more challenging to operate.
4. Due to their compact size, they are more prone to acoustic feedback and often cannot accommodate FM systems.
5. Like ITE hearing aid, they are more susceptible to damage from cerumen (earwax).
6. Similar to ITE hearing aid, they can cause an occluded or "plugged" feeling in the ear.

Currently, the power output of commonly used in ear canal hearing aids is generally suited for hearing loss up to 80 dB, with some high-power models from certain brands reaching 90-100 dB, though these are less common clinically. These devices are typically recommended for:

Younger individuals with mild to moderate hearing loss who have high demands for hearing aid cosmetics and performance.

Middle-aged and elderly individuals with mild to moderate hearing loss, good manual dexterity, and high requirements for both the hearing aid's effectiveness and appearance.

Patients with an average hearing loss below 80-85 dB. For those with a descending hearing loss curve (better low-frequency, poorer high-frequency hearing), in ear canal hearing aids can provide more effective high-frequency gain compensation.