MEMS Microspeakers Blast Sounds From the Fab

The future of audio is silicon.

Image courtesy of AudioXpress

That, at least, is the pitch from audio company xMEMS, which recently announced the availability of the world’s “only all silicon, solid-state fidelity micro speakers.” Designed by xMEMS and produced by Taiwan Semiconductor Manufacturing Co. (TSMC), the speakers pair the consistency and efficiency of modern silicon fabrication with unique audio properties that, xMEMS says, traditional coil speakers can’t match.

Brian Lucey, a mastering engineer with credits on nine Grammy-winning albums, is impressed. “It’s a huge, huge leap in phase accuracy that we’ve never heard before,” he tells IEEESpectrum.

“Everything is hitting you at the same time. There’s no time smear in the way the sound comes across.”
—Brian Lucey, Magic Garden Mastering

Silicon sounds purer

The company says the audible advantages of their silicon microspeakers are found in a technical aspect of audio quality that casual listeners rarely think about: phase distortion. This describes variation in the timing of low, mid, and high frequencies, and it’s an expected element of sound reproduction caused by limitations in traditional coil speakers. xMEMS also benefits from the excellent consistency of semiconductor manufacturing, which should drastically reduce differences in phase accuracy between speakersproduced with the same process.

“Phase inaccuracy is so ubiquitous that we simply accept it,” says Lucey. “Driver technology up to now has never been able to be this accurate. It’s really not a question of what does it sound like when it’s inaccurate, because that’s just normal to our ears. It’s more a question of what does it sound like when it’s this near perfectly accurate.”

xMEMS says their microspeakers achieve phase accuracy using silicon membranes that are quicker and stiffer than any coil speaker. Lucey says the US $100,000 hi-fi speakers he uses for mastering achieve a phase shift of roughly 7 degrees (on a scale of zero to 360). By comparison, silicon microspeakers can reduce the phase shift to roughly 1 degree. “Everything is hitting you at the same time. There’s no time smear in the way the sound comes across.”

Silicon speakers also provide a surprising practical advantage: lack of fatigue. “I don’t have to crank it up to get low end, and there is no pistonic pressure from the swinging barn door design,” Lucey notes, adding that “after hours of listening, there’s no fatigue at all.” The lack of pressure makes for a relaxed listening experience he says he finds comfortable over long sessions.

Semiconductors cut costs, boost efficiency

xMEMS is shipping three versions of its microspeakers to target different applications, but they all share a monolithic silicon design that relies on the company’s namesake technology, MEMS (micro-electromechanical systems). MEMS combine mechanical and electrical components but are fabricated using semiconductor techniques like those that produce integrated circuits.

“Especially for MEMS fabricated with a monolithic process, you will have a transducer that’s consistent and waterproof,” says Mike Klasco, president of Menlo Scientific. “You don’t have to solder it by hand to a circuit board, it can be a pick-and-place” for surface mounted (also known as SMT) electronic components.

Using semiconductor fabrication for audio devices isn’t a novel idea. MEMS technology hit the microphone market in 2007 and has gained roughly 80 percent of global microphone market share. MEMS microspeakers proved a tougher nut to crack, but several companies have achieved breakthroughs over the last few years. This includes Arioso Systems, which was purchased by Bosch in 2022, and USound, which offers several MEMS microspeakers and amplifiers.

A rapid reduction in cost was the key to MEMS’s success as an alternative to existing microphone technologies, and that reduction stems from the efficiency gained by moving production off costly assembly lines and onto efficient semiconductor fabrication provided by foundries such as TSMC. Companies designing MEMS speakers can operate more like fabless chip companies, focusing on architecture while outsourcing production to foundries.

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