Hearing care professionals want their client to have a great hearing aid fitting experience. . But what does that take? For precise results and a good fit, collecting individual data beyond the audiogram and the selected acoustic coupling is essential. One such example, is performing the ‘Feedback & real ear’ test in Phonak hearing aids directly in the client’s ear. This test combines the individual feedback threshold, RECD data, and acoustic parameters to create a more accurate fitting calculation. Perceiving feedback from hearing aids can affect sound quality and client satisfaction. Feedback is the leakage of sound from the hearing aid receiver back to the microphone. This soundwave leakage from the output back to the input produces a form of instability resulting in an audible oscillation.1 Amplified sound is returned to the microphone and this closed loop of sound transmission is continuously amplified to the point at which a tonal squeal occurs.
Phonak’s feedback management system consists of two parts: static and adaptive.
In Phonak Target, the static feedback threshold sets the limit to the maximum available gain before feedback instability occurs and it is applied all of the time. The adaptive phase canceller, known as WhistleBlock, cancels out transient feedback created in the real world, such as when putting a phone to your ear or wearing a hat. Performing a Feedback & real ear test can reduce incidences of feedback. It provides a true representation on how much sound leakage will reach the client’s ear canal for a given frequency.
Did you know there are no tones played during a feedback test?
All sounds heard during the test are audible feedback created by high gain in the single frequency band being tested. The test applies gain one frequency at a time across the frequency range and increases the gain until feedback occurs. Then, the gain level where feedback occurs is the feedback threshold.
Therefore, it is important that the information entered into the acoustic parameters section within the fitting software matches what the client is wearing in the ear, and that the insertion of the hearing aid is appropriate.
What makes a feedback test result unacceptable?
An unacceptable feedback test is when the hearing aid is not able to reach prescribed target gains due to a reduced feedback threshold. The client may experience either feedback or reduced amplification, affecting client satisfaction.
Something to remember is that hearing aids apply the most gain to soft speech inputs. If a client reports they cannot understand or hear the difference between an «s» and «sh», evaluate the feedback test. If the measured feedback threshold is running into the soft gain curve, this could be causing part of the issue.
In the event that the feedback test result is unacceptable, there are steps you can take to improve the result. These include:
- Check for full insertion. Reinsert the hearing aid.
- Change the acoustic coupling or modify the vent.
- For a RIC hearing aid with a dome, adjust the dome size or shape to a more occluded option, or select a different receiver – consider going up one power level.
- For a custom hearing aid or custom earmold, temporarily occlude the vent. If the feedback outcome is better, readjust the vent to be more occluded or send the device in for a vent change. If there is no change in the feedback test, then the fit of the hearing aid might be the issue. Modify the device in-house for a tighter fit or request a remake.
- Check the receiver angle of the device when it sits in the client’s ear by taking another earmold impression and holding it up to the device. By comparing the earmold impression and the device side by side you can see if the receiver might be bumping into ear canal wall. If it is, send the device in for a remake.
Once the issue has been resolved and you are satisfied with the feedback test result, ensure there is enough headroom and gain to meet any potential changes in the client’s hearing loss.
Wait, there is more with Phonak Paradise hearing aids!
Within Paradise hearing aids, the feedback system has been enhanced to provide you with more control and flexibility. You can now overtune the feedback threshold to achieve the gain limit desired. The gain limit can be increased up to 12 dB. In the Feedback & real ear test tab within Phonak Target, the visualization in the curve display and in the legend provides a transparent representation of the feature.
When would I overtune?
Consider overtuning the feedback threshold when you are unable to perform a measured feedback threshold on the client and you see in the curve display, that the feedback threshold limits the gain. The estimated feedback threshold is the estimation that in most clients’ environments they will not experience feedback, but it is not personalized to the client’s specific ear anatomy. Overtune the feedback threshold until prescribed target gains can be reached and the client does not perceive any whistling nor distortion.
Another example of when to overtune is for clients who strongly prefer an open fit, but you see the feedback threshold running into the gain curves. You can overtune the feedback threshold to reach prescribed target gains and with every applied step, you and the client can evaluate sound quality, gain, and feedback tendency.
The benefit for you is the ability to set the management system in the most reasonable way, especially where you are unable to run a feedback test on the client. The benefit for the client is a more optimized fitting.
Overall, feedback is an important topic because it impacts client satisfaction and experience. Fortunately, there are steps you can take to improve both. First, ensure hearing aid insertion and the acoustic coupling are appropriate for the client and that what the client is wearing matches the information entered into Phonak Target. Second, with Paradise hearing aids, overtune the feedback threshold if it reduces the available amplification your client could benefit from.. I believe that with this additional flexibility in managing the feedback system, clients can experience a good hearing aid fit.
To learn more, an eLearning module on feedback threshold overtuning is available on Phonak Learning (accessible in participating countries). For more information, please visit https://learning.phonakpro.com.
1 Agnew, J. (1996). Acoustic feedback and other audible artifacts in hearing aids. Trends in Amplification, 1(2), 56-72.