Technical Key Points of Open Fit Hearing Aids
There are three main reasons why some hearing-impaired people are unwilling to wear hearing aids:1. When wearing it, it is not beautiful and has psychological pressure.
2. Wear uncomfortable, unable to adhere to;
3. The amplification effect is not good and the speech clarity is poor.
With the development of hearing aids technology, hearing aids have become smaller and more beautiful, with greater gains and higher speech clarity. But comfort has always been a difficult problem for audiologists, but at the same time it is the quality that hearing aid users pay more and more attention to. In recent years, there has been a new concept of matching - Open matching, which greatly improves the comfort of wearing hearing aids.
Ear plugging effect:
Sound changes as it passes through the external auditory canal to the tympanic membrane:
· Auricular canal resonance increases external sound by 20-30 dB.
· Bone conduction improves the low frequency of the voice, and the normal ear canal is open, so it is not easy to detect this change. Blocking the ear canal can enhance the low frequency signal and weaken the resonance of the ear canal. In traditional hearing aid matching, the sound is blocked in the ear canal, which sounds hollow and shocky, especially when the wearer speaks, chews or swallows himself. Ear plugging also changes the resonance characteristics of the ear canal, making the wearer's voice change when he listens to others. This condition is more common in patients with better low-frequency hearing. Ear plugging effect is the main problem in traditional hearing aid matching, and open matching can solve this problem well.
Principles and advantages of open fit digital hearing aids:The ear mould of customized machine and ear-back machine can add air holes to reduce the ear plugging effect, but the effect is not obvious when the diameter of air holes is less than 3.2 mm.
Due to volume limitation, it is difficult for custom machine to make ventilation holes with diameter more than 2 mm. In addition, the existence of ear mould of custom machine and ear back machine still changes the structure of the external auditory canal and affects the resonance of the auditory canal.
Thus, in order to completely solve the ear plugging effect and improve the comfort of matching, open matching has become the best choice. Open fitting keeps the ear canal open naturally, does not change the natural resonance of the ear canal. Low frequency signals can be released, avoiding vibration and stuffiness, and most importantly, it also compensates for hearing loss.
Problems that may arise in open testing:Gain: Hearing loss people often have fluctuations and changes in hearing. Hearing aids need to be compensated according to the actual situation.
For descending hearing loss, low frequency loss is light and high frequency loss is heavy, so low frequency compensation is less, while high frequency compensation is more, and vice versa. For steep drop hearing loss, the gain of hearing aids must be more accurate, otherwise the compensation of high and low frequencies is difficult to balance.
In the case of open matching, although the ear-plugging effect disappears, the low frequency signal below 1000 Hz also loses about 30 dB, which has a certain impact on the understanding of speech. Therefore, open matching must provide more gain for low frequency.
Acoustic feedback: The amplified sound emitted by the receiver is collected by the microphone, and then amplified circularly until the final scream occurs. This phenomenon is called acoustic feedback. The greater the gain, the more likely acoustic feedback is to occur, so patients with severe hearing loss should avoid using ventilators. An excellent feedback control system is essential for open matching. The adaptive acoustic feedback control system can track and eliminate the feedback signal without affecting the normal gain, thus maintaining good sound quality.
Excellent acoustic feedback control system is the basis of open test. At present, open matching has been applied to some patients with severe hearing loss.
Signal processing time: It takes time for the hearing aid to amplify the sound, that is, there is a time difference between the sound produced by the hearing aid and the real sound. In the open test, the real voice and the sound from the hearing aids reach the tympanic membrane one after another. Normally, the wearer can not detect them, but if the time difference exceeds 10 ms, the wearer will hear the echo. Therefore, the digital signal processing time of the open auditory aids should be shortened as far as possible, which has a high requirement for the chip's operation ability.
Shape: Open fit digital hearing aids need no ear hook and transmit the amplified signal to the auditory canal through a transparent hose. There is no need to make ear mold or customized machine shell. It is more concealed than traditional ear-back machine. It is comfortable to wear and has no sense of oppression and blockage.
Open matching is a very important direction in the development of hearing aid technology. The purpose of using open matching is to make more patients with hearing loss (especially those with mild and severe hearing loss) have a better listening experience.
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