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Exotic New Silicon-Based Speakers Are Coming to Next-Generation Earbuds

Me, me, me! I'm an early adopter. I gotta have a pair of these bad boys.

Exotic New Silicon-Based Speakers Are Coming to Next-Generation Earbuds

Speakers the size of an asterisk have the potential to change the way we reproduce sound, cope with hearing loss—and even make objects in virtual reality feel real

By Christopher Mims, WSJ

July 21, 2023 9:00 pm ET

The way humans reproduce recorded sound could change more in the next decade than it has in the past century.

What’s coming are solid-state speakers, etched from wafers of ultrapure silicon—like microchips. That means they operate like nothing available today—and also that they have capabilities that no existing sound-reproduction system can match.

This technology also embodies a broader trend—the conversion of all electronic components to solid-state silicon—that is easy to take for granted, but has had profound consequences for how we interact with the world.

Sound production has long been a holdout in the march toward solid-state everything. While speakers have remained relatively unchanged, nearly all the components in our phones, from sensors to the antennae that allow them to wirelessly connect, are all now made by the billions with the same technology, and most of the same materials, used to make microchips.

An exploded view of one of USound’s MEMS speakers. PHOTO: USOUND

The technology that has made this transition possible, called MEMS—short for micro-electromechanical systems—is the reason an entire 1990s RadioShack’s worth of gear can be crammed into the slim slabs of touch-sensitive glass that now fit in our pockets.

So far, in speakers, there are only a handful of products shipping that use MEMS technology. I’ve tried one product—a prototype in-ear monitor, of the sort used by audio engineers—and was impressed by its performance.

Peter Cooney, founder of SAR Insight & Consulting, which tracks the audio-technology industry, has been following the world of MEMS-based, or solid-state, speakers for a decade. And this year and the next are, he says, when they will finally arrive in the kinds of devices regular consumers might buy, such as high-end wireless earbuds.


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One company building this tech, xMEMS, has made available prototypes of its speakers to dozens of companies, and over 30 of them are working on earbuds and other products based on the technology, says a company spokesman.

One recipient of prototype in-ear monitors—the kind of high-fidelity earbuds professionals use when mastering musical tracks—is Brian Lucey. A mastering engineer of nine Grammy award winners, Lucey told me that the solid-state speakers in the in-ear monitors he’s using have become indispensable.

But eventually, this tech could be everywhere—in every smartphone, and in nearly all the earbuds, smart glasses, and various other “hearables” that are on their way to market. Indeed, there is reason to think these solid-state speakers could come from a familiar brand in the not too distant future. One of the manufacturers working on integrating it into consumer devices, China-based Luxshare, manufactures Apple’s AirPods, as well as its new Vision Pro headset.

Luxshare and Apple did not respond to requests for comment.

From Alexander Graham Bell to nanoscale manufacturing

The things that make sound inside most speakers—whether they’re the kind attached to your stereo or those inside a pair of earbuds—nearly all operate on the same principle. The first working example of this idea was introduced in 1876, in a loudspeaker designed for the first telephone, by none other than Alexander Graham Bell. (If you want to get fussy about it—and I know audiophiles reading this will—it was the improved version of this idea, pioneered by the founders of Magnavox in the early 1900s, that is the most direct antecedent to today’s speakers.)

A micro speaker module from XMEMS. PHOTO: XMEMS

It works like this: Inside the speaker is a magnet, and inside that is a coil of wire, which is attached to a stiff but flexible membrane—which you’ve seen if you’ve ever taken the grill off the front of a speaker cabinet. Pulses of electricity traveling through the wire are turned into vibrations, which the membrane translates into the movement of air that we call sound.

Since its invention, engineers have made innumerable improvements to this design, without fundamentally changing it. Those improvements are why today’s speakers can fit into a smartphone or a hearing aid.

MEMS-based speakers consolidate all those parts into a single unit. As a result, it can be much smaller, while also offering greater clarity, and potentially requiring less power. These speakers use a principle already widely exploited in MEMS-based devices, called piezoelectricity.

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Piezoelectric substances move when you put electricity through them. Some of them move quite fast. For example, the tiny, comb-like antennae in your phone vibrate billions of times a second. These substances can be made from silicon, with a thin film of piezo materials added on top.

Austria-based USound, which along with Santa Clara, Calif.-based xMEMS appears to be in the lead in bringing this tech to market, makes solid-state speakers that use tiny amounts of piezoelectric material layered on top of silicon to move a piston that attaches to a membrane, to generate sound. In a way, it’s as if the engineers at USound replaced the coil of wire and the magnet in a typical speaker with a piece of silicon.

The engineers at xMEMS take things a step further—their entire speaker, including its vibrating membrane, is fashioned on a wafer of ultrapure silicon—the same kind that are used to make all the microchips that are the “brains” of nearly every computing device in the world.

MEMS-based speakers could be as little as 1 millimeter thick, a quarter of the thickness of what are typically the smallest speakers used in devices like smartphones and earbuds, says Andrea Rusconi Clerici, chief technology officer of USound which was founded in 2014. USound already has at least one product on the market: a pair of glasses equipped with a MEMS speaker. USound’s latest speakers are 5 millimeters long and 1.4 millimeters wide—or about the size of an asterisk in a printed book.

Music like you remember it

The biggest application for this technology is the market for wireless earbuds, which is about 400 million pairs a year, says Cooney. These range from $20 buds you find on Temu to $300 models from the likes of Bose and Apple.

Of course, to get traction, the technology actually has to offer something you can’t get with today’s conventional earbuds.

So I tried it out for myself. The short version of my experience is that, while the best of today’s earbuds, such as AirPods Pro 2, are great at delivering warm sound and clear calls, there’s a fair amount we’ve all been missing, and it’s part of the reason that listening at home, even on the best gear, still can’t compare to live music.

I was surprised to find that trying out some favorite tracks on solid-state earbuds exposed details—even instruments—I hadn’t noticed before, and which I couldn’t pick out using even high-end conventional in-ear buds. I could have a similar experience using expensive speakers with distinct woofers and tweeters at home, but the whole point of this technology is that it can fit in your pocket and go anywhere.

This 8-inch silicon wafer contains hundreds of micro speakers. PHOTO: XMEMS

Part of the reason solid-state speakers can deliver clearer sound is that tiny pieces of piezoelectric silicon can move more immediately and precisely, says Lucey, the mastering engineer. “Ideally, a perfect speaker goes when you tell it to go, and when you say stop it stops moving, and this does a lot of things that are closer to that ideal,” he adds.

Possible futures of silicon-based audio

If major players in the audio industry do adopt solid-state speakers, the transition is likely to take years, even decades. And these kinds of speakers might forever be paired with conventional ones, which are for now much better at producing bass.

Producing low-frequency sound is critical not just for helping people feel the groove, but also for the noise-canceling ability of today’s earbuds. That could mean that future earbuds would have separate drivers—one conventional, and one solid-state.

But earbuds, and later, over-the-ear headphones, are only the beginning of what’s possible for these devices.

Once a mechanical object can be fashioned out of silicon, it can find all sorts of unexpected new applications. For example, the first inertial measurement unit—used to determine the movement and orientation of an object—was created for the Apollo spacecraft, and was as big as a basketball. The solid-state version of it is the size of a grain of sand, and is the reason your phone knows when you’ve switched between portrait and landscape mode. (It’s also the reason smartwatches can recognize when you’re working out.)

One currently exotic but potentially transformative application for solid-state speakers, still in the prototype stage, is making objects that exist only in augmented and virtual reality feel real. It turns out that by using arrays of tiny speakers, it’s possible to generate a field of ultrasonic sound that exerts force on the human hand. This could make it possible, for example, to simulate two people shaking hands in VR—or the feel of an object that is only virtual.

Another potential application—far off, for now—is implantable speakers for people with hearing loss, says Cooney. Meanwhile, recent changes made by the FDA have made it possible for companies to sell over-the-counter hearing aids. Because solid-state speakers excel at generating the higher frequencies where hearing loss occurs first, they could be ideal for this application.

Apple doesn’t sell over-the-counter hearing aids. But its AirPods Pro can already function as a pair of them, for people with mild-to-moderate hearing loss. Whether or not Apple uses MEMS-based speakers to enhance this capability in the future, one of its competitors is likely to try.

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