The Future of Hearing Aids: xMEMS Develops All-Silicon, Solid-State Micro Speaker

The market for hearing aids is rapidly changing. With the rise of wider over-the-counter availability and increasingly “earbud-like” designs, hearing aids are evolving from purely medical products into true lifestyle devices that combine the best features of Bluetooth earbuds (media streaming) and hearing instruments (voice amplification). 
 
Unfortunately, the current speakers inside most hearing aids are unable to fully deliver on low frequency sound — which are essential for true media reproduction. That’s according to xMEMS, a semiconductor company out of Silicon Valley, which has developed the “world’s first all-silicon, solid-state micro speaker” for use in hearing aids. 
 
I recently spoke with Mike Housholder, VP Marketing and Business Development at xMEMS to explore their technology, the benefits for both hearing aid wearers and manufacturers and why he believes silicon MEMS speakers will soon dominate the hearing aid market.
 
Tom Terzulli: Describe your technological breakthrough. What is a Silicon MEMS speaker?
Mike Housholder: xMEMS has created the world’s first all-silicon, solid-state micro speaker. For over a century, the moving coil speaker (also referred to as a dynamic drive speaker) has been the primary technology for sound reproduction. The coil speaker is a multi-component mechanical assembly consisting of a voice coil, magnet, chassis/frame, paper/plastic diaphragm/cone, dust cap and spider (suspension). xMEMS has consolidated all of these functions into a single piece of silicon, creating a monolithic structure to reproduce sound that is inherently more uniform, consistent, reliable, lighter weight, with improved audio resolution and detail vs. the legacy architecture. Our MEMS speakers replace the coil and magnet actuation mechanism with a thin-film piezo layer (a layer in the semiconductor wafer) and we use silicon to replace the paper/plastic diaphragm.
 
TT: What kind of speakers do hearing aids currently use? What do they struggle to accomplish that MEMS can do better?
MH: Hearing aids primarily use balanced armature (BA) speakers which are a derivative of the moving coil architecture. Balanced armatures have traditionally been favored in hearing aids due to their small, compact size (vs. dynamic drive coil speakers) and their efficiency/low power consumption since medical-grade hearing aids typically require at least 18-hour battery life (per day). Also, balanced armatures provide high-quality audio in a narrow bandwidth which is ideal for voice amplification since the human voice only operates within a narrow frequency range. Balanced armature manufacturing, though, is complex and is not automated. Humans hand-assemble these devices which increases part-to-part variability and constrains production capacity.
 
xMEMS’ speakers, specifically our small Cowell device, bring several advantages to this market:
 

• Size: xMEMS Cowell is even smaller in total area/size vs. balanced armatures which enables the same deep insertion into the ear canal.
• Wider bandwidth: Cowell is a full-bandwidth speaker and is capable of producing the full human hearing frequency range (20Hz-20kHz). So, not only can Cowell amplify voice, but can also be used for amplifying rich, complex media (music, movies, etc.). This is increasingly important, since new hearing aids are increasingly including Bluetooth connectivity with our smartphones, TVs and other media devices. Consumers will demand their hearing aids to amplify full-bandwidth content, not only voice.
• Reliability: Solid-state MEMS speakers are inherently more reliable and robust than BA. They are more robust to drop/mechanical shock and are IP58 rated for moisture/dust/particulate resistance. xMEMS speakers even survive washer/dryer cycles. This leads to fewer failures at the consumer.
• Automated, high-volume production: With the new OTC initiative, consumer demand for hearing-assistance devices is expected to increase dramatically. xMEMS high volume manufacturing capacity will be able to support this increased demand where BA suppliers may struggle to keep up.

 
TT: What types of hearing loss are xMEMS speakers best equipped to address? Are there any types of hearing aids that they work best with?
MH: Being a full-bandwidth speaker (20Hz-20kHz), xMEMS speakers are appropriate for any type of hearing loss. However, hearing loss is most common in the range of 2kHz-8kHz and the characteristic frequency response of xMEMS’ speakers aligns well with this. xMEMS speakers exhibit a linear, increasing gain starting at 850Hz out beyond 10kHz. So our speakers have sufficient headroom/gain to support high-frequency hearing loss in this region and beyond.
 
TT: Are there any benefits for hearing aid wearers outside of sound quality?
MH: Yes. xMEMS solutions offer additional benefits to wearers in terms of comfort. First is in reduced weight (no magnet) vs. balanced armature. Receiver-in-canal (RIC) hearing aids mount the speaker deep in the ear canal. Over extended wear time, a lower weight speaker will be more comfortable. Second, and most differentiating is venting. xMEMS venting advantages come in two forms:
 

1. Traditional coil architectures typically are not vented. So, as the speaker diaphragm pushes air to generate sound, it can pressurize the ear canal leading to long-term discomfort in the eardrum. The speaker diaphragm in xMEMS speakers is vented. As it actuates, the vented diaphragm allows any air pressure build-up to escape out the back of the speaker and won’t pressurize the eardrum.
2. The second comfort challenge with hearing aids is balancing open-fit and closed-fit eartips for managing occlusion effects. xMEMS has a novel active vent solution for this called Skyline. Skyline is a separate chip using the same piezoMEMS platform as our speakers. The Skyline vent can be opened to remove occlusion effects for improved wear comfort, behaving like an open-fit eartip. Alternatively, Skyline can be closed to provide the best passive isolation when a closed-fit wear is preferred. Skyline makes the hearing aid more flexible and adaptable to multiple wear/use scenarios.  

 
TT: How about HA manufacturers? How do you convince them to transition over from their current speaker architecture?
MH: The benefits of xMEMS speakers are readily apparent to any experienced HA manufacturer. Wide-bandwidth for voice and media reproduction, small size, lower weight (no magnet), no electromagnetic interference between speaker and Bluetooth wireless due to the fact that our speakers don’t have magnets. High volume manufacturing. Venting for increased comfort.
 
TT: Where does xMEMS fit in with the expansion of over-the-counter hearing aid and consumer “hearable” options?
MH: As discussed above, our high-volume manufacturing advantage aligns well with the OTC initiative as the consumer adoption of hearing assistance devices increases to unit volume levels that BA manufacturers can’t accommodate. Also, our wider-bandwidth sound reproduction aligns well with these newer media-centric, Bluetooth-connected hearing assistance devices.