At present, the three types of hearing aids that are commonly seen in the market have the following characteristics:
1.Box-type hearing aids are relatively cheap, but have the disadvantages of being too large, inconvenient to use, and having fewer functions.
2.The back-of-the-ear type is worn behind the ears, and has a relatively small and light appearance. It has a variety of grades and different functions. There are many users at present.
3.The main advantages of customized hearing aids are: small and exquisite appearance, good concealment; customized according to the shape of the ear canal, comfortable to wear, and will not fall; not easy to enter water or sweat, which is conducive to the maintenance of hearing aids.
Blind purchase Hearing aid , It will only increase the burden on one’s own ears and bring inconvenience to life.Fully understanding the nature of your deafness and the degree of hearing impairment can greatly increase the chance of choosing the correct hearing aid.According to the International Health Organization (WHO-1997) Grading hearing loss, averageHearing loss≤25 It is normal in decibels;≤26 ~ 40 Decibel is a mild hearing loss;≤41 ~ 60 The decibel is moderate hearing loss; ≤61 ~ 80 The decibel is severe hearing loss;≥81 The decibel is extremely severe hearing loss.Patients with severe hearing loss need to consider three factors: hearing threshold, discomfort and appropriate loudness level (UCL) And auditory resolution.
How to choose if the hearing loss is severe Hearing aid ?The traditional solution is to use high-power linear hearing aids. In this type of hearing aids, a method of providing high gain is adopted to provide sufficient amplification to obtain speech audibility.
XNUMX. Features of Extremely Severe Hearing Loss
The most important feature of severe hearing loss is that the injustice of hearing loss is manifested in the decrease in sensitivity and affects the ability to process various sounds; although the sound can be heard, it cannot effectively extract useful information from the signal.
Three, processing method
1、Linear amplification In the past, only linear hearing aids could provide the required gain50 ~ 70 dB) Harmony output (130~ 140 dB SPL ) To meet the needs of patients.So a lot of wear10 ~ 30Patients with hearing aids used linear super-power hearing aids, which use peak clipping, which is the most direct output limiting method.In recent years, some ultra-high-power and high-quality hearing aids have entered the market, using clearer output control circuits.The output compression system is designed to limit the amount of amplification and the electrical loudness output of the receiver by highly compressing the signal.
The advantage of this compression method is that it does not introduce distortion caused by peak clipping when limiting.However, it has been clinically shown that users of ultra-high-power hearing aids do not respond well to the seemingly better effects of this compression system.Because the minimum distortion can guarantee good signal quality is only the opinion of normal hearing people, and compression has changed the nature of sound that users of ultra-high-power hearing aids have been accustomed to for many years.In addition, the use of acoustic output to limit the compression is reduced at the maximum gain and maximum output1 ~ 2 dB , And this small change will have a negative impact on the listening of some patients with extremely severe hearing loss.
2, Non-linear amplification Fully automatic non-linear amplification patients can obtain better audibility for soft speech signals, and provide better sound quality for medium and strong sounds. As the hearing loss intensifies, it is necessary to increase a certain gain and compression accordingly. The full range of speech is put into the residual dynamic range.By analogy, putting the entire speech range into the residual dynamic range of patients with severe hearing loss requires a large compression rate.
However, providing more gain and compression to match the dynamic range of patients with severe hearing loss is limited because the signal at some frequency points is not available to the user.The fast compression system minimizes the impact of the instantaneous amplitude fluctuation of the signal. Normal hearing ears can extract useful signals from the compressed signal, but severely impaired ears cannot handle such compressed signals well.The full-range speech signal is compressed in a small residual hearing range. This flat signal profile cannot be used by some extremely severe hearing loss ears. Therefore, it is attempted to use wide dynamic compression to solve the problem of hearing aid selection for extremely severe hearing loss. restricted.The use of nonlinear amplification to solve this type of hearing problem is still restricted.
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