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Howling is a major cause of users’ dissatisfaction with hearing aids, and it is also a major problem encountered by the opticians in the process of hearing aid debugging.

Currently, each Hearing aid Manufacturers will use “feedback suppression” technology to solve the user’s howling problem.

So, do acoustic feedback and howling say the same thing?

1. The relationship between acoustic feedback and howling

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

Howling is an audible oscillation (audible oscillation) generated on the basis of acoustic feedback. Howling occurs only when the sound repeatedly enters the feedback loop and is repeatedly amplified.

In fact, acoustic feedback is a phenomenon that often occurs in the working process of hearing aids. Howling 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.Feedback does not necessarily have howling. What we usually call acoustic feedback is not exactly howling.

2. What level of feedback will cause howling

The sound leaking from the residual ear canal 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 to form a loop, and then generate audible sound oscillations, causing howling .

For example, if the amplified sound intensity of the hearing aid can reach 90dBSPL, after the residual ear canal attenuation, the sound intensity picked up by the microphone again is 60dBSPL, then the critical value of howling caused by the hearing aid is 30dBSPL.

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

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

3. What factors are related to howling?

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

01, gain

Howling is related to gain, not to maximum output.

If the gain of a high-power hearing aid is the same as the gain of a low-power hearing aid, then they have the same possibility of howling.

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

02, phase shift

Phase shift, that is, 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 howling.

03, ear canal attenuation

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

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, howling will not occur;

If the attenuation value is less than the gain value after hearing aid, it will increase the possibility of howling.

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

Only by understanding the ins and outs of howling can we solve the problem of howling in the correct way.

Are feedback and whistle the same thing?  https://www.jhhearingaids.com/