Hearing aid manufacturers are constantly striving to improve speech intelligibility and comfortable listening, with researchers investigating computer-aided technology to design better hearing aids by improving sound transmission, reducing noise interference and feedback.
According to Poul Kristensen, Senior Acoustic Engineer at GN ReSound: "The big challenge in hearing aids is to have high gain and to have that, you need to be able to control your feedback. It's a very small device for gain that is sometimes up to 80dB, so you need many different tools to understand the feedback patterns."
In hearing aids there are different vibration-borne feedback patterns, meaning the small speaker inside generates high-pressure sound that makes the whole device vibrate. This vibration generates sound, and if the sound path from the speaker to the output is not insulated you can also have direct sound feedback. For development prototypes this is especially important.
GN ReSound looked for a system that could provide accurate conformal mapping on the small scale that they were looking for - and do so automatically and unattended. Seeing a robotic system already made for another customer, by Brüel & Kjær's Customised Project Department, was important to GN ReSound's decision, as it demonstrated the effectiveness of the system in action.
Poul Kristensen says: "At the time we were looking for a system it was taking an unpredictable amount of time in Research and Design to get the device performance and gain that we were looking for, because the feedback pattern is so difficult to understand. We had to do a lot of experiments without seeing the whole picture, so it took us a long time and the time taken wasn't predictable. We wanted to get into a situation where things were more predictable, with a better understanding, so we could be more professional with better tools. This was one of the tools to build up our simulation models and understanding."
GN ReSound preferred a robotic approach for the accuracy and repeatability that it could offer. They chose a turnkey system from Brüel & Kjær using Statistically Optimised Near-field Acoustic Holography (SONAH) made by the Customised Project Department. The full case study is available to read on www.bksv.com.