Whistling is one of the main reasons for users’ dissatisfaction with hearing aids, and it is also a big problem encountered by the match examiner in the process of hearing aid debugging.

At present, all hearing aid manufacturers will use “feedback suppression” technology to solve the problem of users’ howling.

So, is acoustic feedback the same thing as howling?

1. The relationship between sound feedback and Howling

When the microphone picks up the sound from the receiver, the sound will enter the receiver and be amplified twice, thus forming the feedback loop of the sound.

Howling is an audible vibration based on sound feedback. Only when the sound repeatedly enters the feedback loop and is amplified, can it appear.

In fact, acoustic feedback is a common phenomenon in the working process of hearing aids. Only when the feedback is large enough to cause the sound to oscillate, will there be a scream.

Therefore, feedback is a mechanism, whistling is a phenomenon, and they are not the same concept. There is no need to scream when there is feedback. What we usually call acoustic feedback is not entirely scream.

2. What level of feedback will cause screaming

If the sound leaks from the residual ear canal, it will reach the microphone again. If the distance is not enough to attenuate the sound leaking from the residual ear canal, the hearing aid will gradually stack the sound, form a loop, and then generate audible sound oscillation, causing howling.

For example, if the amplified sound intensity of the hearing aid can reach 90dB SPL, and the sound intensity picked up by the microphone is 60dB SPL after the residual ear channel is attenuated, the critical value for the hearing aid to generate squealing is 30dB SPL.

At this time, if the gain of the hearing aid exceeds 30dB, it may cause squealing.


< img SRC = "http://sky.hearingaid.cc/data/images/2019-10-21/1dc49a0af3445e71cb62cb5b6a61bbab. PNG" ALT = "squealing and feedback of hearing aid" >

As shown in the figure, it is the path schematic diagram of the feedback generated inside the hearing aid.

The blue arrow represents the sound propagation path amplified by the hearing aid; the red arrow represents the feedback path generated after the sound leakage.

3. What factors are related to howling

The generation of howling mainly comes from the following three aspects:

01 gain

Whistling is related to gain, not to maximum output.

If the gain of a high-power hearing aid is the same as that of a low-power hearing aid, the possibility of their squealing is the same.

The reason why we think that high-power hearing aids are more likely to produce squealing is that the maximum output of high-power hearing aids is larger. When it causes squealing, the vibration of hearing aids will be more intense than that of low-power hearing aids, so we think that high-power hearing aids are more likely to generate squealing.

02 phase shift

Phase shift refers to the phase difference between the output sine wave signal and the input sine wave signal.

When the phase shift in the loop is an integral multiple of 360 °, it will cause a howl.

03 attenuation of auditory canal

The process in which sound is emitted from the receiver and picked up again by the microphone is called sound leakage.

Because the ear canal will attenuate the leaked sound, the sound intensity from the receiver is actually greater than that received by the microphone.

If the attenuation value is greater than the gain value after hearing aid, no whistling will occur;

If the attenuation value is less than the gain value after hearing aid, the possibility of whistling will be increased.

Whistling is an audible sound oscillation based on sound feedback, and it is also an important factor affecting the sound quality of hearing aids.

Only when we understand the origin and the development of howling can we solve the problem of howling in the right way.

What’s the difference between screaming and voice feedback? Do you understand?

Jinghao hearing aid reminder: hearing aid wearing requires professional “matching”, so it is very important to choose a professional hearing aid matching center and a hearing aid tester! If you have any hearing problems, you can call Jinghao for consultation, or come to the matching center for experience. Hearing aid free consultation Tel.: + 86-18566295705


Link:What is the meaning of the roar and feedback of hearing aids

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