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Howling is a major cause of dissatisfaction with hearing aids, and it is also a major problem encountered by the fitter during the debugging of hearing aids.

At present, each hearing aid manufacturer uses the “feedback suppression” technology to solve the user’s howling problem.

So, is the same thing about acoustic feedback and howling?

1, the relationship between acoustic feedback and howling

When the microphone picks up the sound from the receiver, the sound enters the receiver and is amplified twice, creating a feedback loop of the sound.

Howling is an audible oscillation generated on the basis of acoustic feedback. Only when the sound repeatedly enters the feedback loop and is repeatedly amplified, whistling occurs.

In fact, acoustic feedback is a phenomenon that often occurs during the operation of hearing aids. Whistling occurs only when the feedback is large enough to cause the sound to oscillate.

Therefore, feedback is a mechanism, and howling is a phenomenon, and the two are not the same concept. There is no whistling in the feedback, and the so-called acoustic feedback is not exactly a howling.

2, what level of feedback reaches the level of whistling

When 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 superimpose the sound, forming a loop, which will produce an audible sound oscillation and cause a howling. .

For example, if the amplified sound intensity of the hearing aid can reach 90dB SPL, after the residual ear canal is attenuated, the sound intensity picked up by the microphone is 60dB SPL, and the threshold value of the hearing aid generating whistle is 30dB SPL.

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

As seen in the figure, a schematic diagram of the path for generating feedback inside the hearing aid.

The blue arrow represents the propagation path through which the sound is amplified by the hearing aid; the red arrow represents the feedback path produced after the sound leaks.

3, howling is related to what factors

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

01增益

Howling is related to gain and has nothing to do with the maximum output.

If the gain of a high-power hearing aid is the same as the gain of a low-power hearing aid, then the probability of their whistling is the same.

The reason why we think that high-power hearing aids are more likely to produce howling, because the maximum output of high-power hearing aids is large. When the whistling is caused, the hearing aids will be more violent than the low-power hearing aids, so we will think of high-power hearing aids. It is easier to produce howling.

02相移

The 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 integer multiple of 360°, it causes a howling.

03Ear canal attenuation

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

Since the ear canal attenuates the leaked sound, the intensity of the sound emitted from the receiver is actually greater than the intensity of the sound received by the microphone.

If the attenuation value is greater than the gain value after hearing aid, no howling occurs;

If the attenuation value is smaller than the gain value after hearing aid, the possibility of howling is generated increases.

Howling is an audible sound oscillation generated on the basis of acoustic feedback, and is also an important factor affecting the sound quality of hearing aids.

Knowing the ins and outs of howling is the only way to solve the howling problem in the right way.

What is the whistle and sound feedback? Have you figured it out?

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