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Helping the World Listen with Hearing Aid Technology

Sonion uses vibroacoustic modeling and experimental tests to develop components for hearing instruments and professional audio. Michele Colloca of Sonion spoke with COMSOL about his team's work and the future of hearing aid technology.

By Joseph Carew
February 2025

Audio monitors, earphones, headphones, hearing aids, and other popular audio technologies often feature the name of a single brand, but most of these products incorporate parts designed and made by a variety of companies. For example, five of the world's six largest hearing aid companies feature transducer components developed by Sonion, a global company that designs and manufactures advanced miniature components — such as balanced armature receivers, high-end microphones, voice pick up sensors, and other electromechanical components — for manufacturers of hearing instruments and professional audio. The engineers at Sonion support their customers at each stage of product development, from initial concept through design refinement and mass production. "Our goal is to become partners with our customers and codevelop with them, rather than just being their suppliers," said Michele Colloca, head of receiver & RIC development at Sonion.

In his work, Colloca can be found leading teams of simulation engineers in the Netherlands and Vietnam, providing different R&D departments at Sonion and their customers with modeling support for existing products and new concepts, validating models with experiments, and explaining the mechanisms behind Sonion's transducers. "We see modeling as a place of mutual enrichment, where we can exchange information and solve problems. Our models are a place where we and our customers can join together to improve the end users' experience," said Colloca.

As captured in the following Q&A, we connected with Colloca to learn about the main challenges in designing hearing instruments, how modeling and simulation helps accelerate R&D, and how Sonion is moving hearing aid technology forward.

What trends and consumer demands are driving new developments in hearing aid technology?

"The main goal of hearing aids is to help people hear better in any environment. This involves improving the audio quality of these devices, particularly their speech understanding in noisy environments. Additionally, it entails enhancing the robustness of hearing aids and improving their visual appearance by making them smaller and less visible, so people want to wear them. Finally, it involves making hearing care more accessible and affordable, so more people are able to make use of hearing aids."

When it comes to designing components for hearing aids, what are the main challenges?

"At Sonion, we design and develop balanced armature receivers for a wide range of hearing aid power levels and applications, in both single and dual configurations; hybrid and electrostatic receivers for specialized and professional use cases; ready-made steel or plastic-based receiver-in-canal (RIC) systems for hearing aids; and miniature electret and MEMS microphones for high-performance and low-power hearing aids (Figure 1).

Therefore, we need to deal with multiple key tradeoffs. For instance, our transducers must be small enough to fit in a hearing aid while performing with low power consumption, minimal distortion, and, in the case of balanced armature receivers, reduced interference from mechanical vibrations, magnetic feedback, and acoustic feedback. In addition, our MEMS microphones need to be highly sensitive to sound but not to vibrations. Further, our components must be reliable and robust against temperature, humidity, and contamination via earwax and dust.

From a modeling perspective, our devices are inherently multiphysics and characterized by strong nonlinearities. For example, optimizing a model's electrical domain can have a negative impact on its acoustical domain and vice versa. Finding the right balance is always a challenging yet fascinating task."

Considering the stakes in this work, what are the consequences of getting a design wrong?

"When an optimal design is not achieved, it can result in the need for multiple design iterations, leading to long development times and higher R&D costs; delays in market and product launches for original equipment manufacturers (OEMs); and missing out on design-win opportunities in bid phases."

Why does Sonion turn to modeling and simulation to help develop hearing aid components?

"Our modeling and simulation work allows us to spend time and resources more efficiently before starting the prototyping phase. Building virtual prototypes in the COMSOL Multiphysics^® software also allows us to achieve faster iterations on design concepts. In addition, with the finite element analysis (FEA) techniques offered in the software, we are able to thoroughly study the behaviors of our products that would otherwise be difficult to measure or observe clearly in a lab."

Can you share an example where you found modeling and simulation especially important?

"In many applications, a balanced armature (BA) receiver can get close to a strong external magnet. For example, this can happen when a hearing instrument, such as an earbud, is placed in the charging case. The charging case can contain magnets to guide the inserted device into position. This can have negative consequences because the external magnet's field can penetrate high permeability components of the BA receiver and interfere with its magnetic operation. As a result, the hearing aid or earbud may malfunction, as the interaction between the external and internal magnetic fields — from the charging case and BA receiver, respectively — will impede the BA receiver's ability to produce sound, or the sound may have high distortion." (Figure 2)

"To analyze this interaction, we created a model in COMSOL^® to analyze the interference of the magnetic flux due to the external magnets with the magnetic flux generated by the BA receiver used to displace the armature. The simulation results showed that when an additional magnetic flux is added by the external magnet to the magnetic path inside a receiver, the flux changes the magnetic reluctances of the entire magnetic circuit and causes the receiver magnets to demagnetize." (Figure 3)

Can you share a second example where you found the use of modeling and simulation useful?

"In professional audio and hearing aid technology, lumped element models are often used as a quick and convenient tool to predict the behavior of audio transducers, such as MEMS microphones. To increase the accuracy of these models, end corrections for a spout or sound inlet, need to be included on the acoustic channel length. These end corrections describe how an acoustic channel is open to the outside environment, such as a channel with an open end or a channel that ends with an opening in the infinite plane, called a baffle. The coefficients that reflect the end correction to the acoustic mass of the spout or inlet are well known. The end correction coefficient for the real part of the acoustic impedance, which corresponds to the channel's acoustic resistance, is typically assumed to be the same as that for acoustic mass. In our study, we used thermoviscous acoustics in COMSOL to introduce and quantify the end correction for acoustic resistance. By doing so, we found that the end correction for acoustic mass can be different from that used for acoustic resistance." (Figure 4)

Why are lumped element models important for audio and hearing technology R&D?

"The key receiver performance indicators, such as electrical impedance, sound pressure levels, and vibration, strongly depend on the design of the transducer itself as well as the acoustic load connected to it. In this case, the acoustic load represents the human ear and the connecting sound channel. The typical device used to model the average human ear is the ear simulator, known as the 711 coupler. However, when considering the entire volume and special features of this ear simulator, as well as the structure of acoustic tubing needed to connect the receiver to the ear simulator, we end up with a very large fully coupled FEA model that is computationally expensive.

We adopted an approach to simulating the acoustic tubing and 711 coupler as a two-port network instead of a fully coupled FEA model. Such an approach can offer significant gain in computational time. We validated the transfer matrix method with the COMSOL Multiphysics software against a complete FEA of a transducer, tubing, and a coupler. Setting up a lumped representation of tubing and a coupler by adopting a transfer matrix implementation reduced model complexity and computational time dramatically. In the end, we were able to test different concepts and quickly select the virtual prototype to develop into a physical one for testing in the lab."

What features in the COMSOL^® software do you find helpful in your daily work?

"We mainly benefit from the easy implementations and flexibility of the Magnetic Fields interface in the AC/DC Module, an add-on product to the software, as well as the Pressure Acoustics, Thermoviscous Acoustics, and Solid Mechanics interfaces in the add-on Acoustics Module. We also benefit a lot from the definitions of magnetic and mechanical material properties in the built-in material library. Furthermore, the visualization capabilities of COMSOL are really powerful, as they can be used to provide clear answers to research questions and present COMSOL data to other colleagues or stakeholders. Finally, the sweep functions, such as auxiliary or material sweep, are particularly useful because they allow for studying the effect of different parameters in one simulation."

How has simulation improved product development at Sonion?

"A virtual prototype cannot replace a real prototype, we will always need to build a physical prototype, measure, and validate the model. But once the model is validated, the virtual prototype will be robust enough to be used for selecting the right design concept. To further illustrate this point, let's consider an example of a prototyping process: When testing a singular design concept, you need one virtual prototype, which takes roughly seven hours to build. However, without a virtual prototype, you would need to build at least 5 samples, test them, and measure them for each concept, which takes 40 hours on average. Therefore, simulation reduces the time required for testing one design concept by a factor of at least 5.7. In this scenario, the number of learning processes per euro invested increased exponentially by adopting virtual prototyping."

How are your products helping to move hearing aid technology forward?

"Sonion products address the key trends in the hearing aid market. We strive to improve the performance of our products and make their audio quality better. New products must adhere to rigorous quality standards, and we continuously push the limits of our products' reliability to enable better and more robust hearing aids. Our product designs take the full hearing aid into consideration, so that we enable manufacturers to make even smaller hearing aids. Finally, we always design cost effective solutions so that we can support more affordable hearing care.

In the future, we plan to further develop our multiphysics models, increase the accuracy of our virtual prototypes by adding variations of component size, drastically reduce our computational times, and improve the parameter vectors for lumped element model-based circuits via FEA investigations."

What role does simulation play in the future of hearing aid technology?

"Virtual prototypes will be more accurate and the gap between them and physical prototypes will be minimized. And thanks to the increase in computer processing speed, the transition from design to testing and from testing to product launch will be rapid.

As for the future of hearing aid technology in general, I believe it will involve advanced signal processing features that improve speech intelligibility in different environments, connectivity, sound quality, robustness, and size reduction. The new hearing aid platforms will include more and more AI for enhancing speech recognition in noise, with a tradeoff on power consumption."