MEMS Silicon Speaker Boasts Breakthrough at Over 140 dB Low-Frequency SPL

In a big leap for solid-state audio technology, today xMEMS Labs is announcing Cypress, its newest MEMS speaker capable of creating high-quality sound across the full range of audio frequencies. Compared to traditional coil-and-magnet speakers, solid-state audio offers many advantages, but until recently has not been able to compete with legacy audio equipment. With Cypress, however, this may no longer be the case.

 

xMEMS’ Cypress uses piezoelectric materials on silicon to produce powerful sound across a broad frequency range, including 140 dB at 20 Hz for adaptive noise cancellation. Image used courtesy of xMEMS

 

In order to learn more about Cypress and the technology behind the MEMS speaker, we sat down with Mike Housholder, vice president of marketing and business development at xMEMS Labs, to find out what allows the Cypress speaker to perform well across a broad frequency range, as well as how the adoption of solid-state speaker technology could change the way we create sound in next-generation applications.

 

Ultrasonic Solid-State Speakers

Compared to traditional speakers using coils and magnets, solid-state speakers leveraging MEMS technology allow designers to leverage mature silicon processes to create audio transducers with better tolerance and uniformity between parts. This is especially useful as electronics continue to shrink since solid-state speakers can allow for comparable audio levels in a smaller package with fewer steps.

 

Coil-driven speakers have more complex parts compared to solid-state speakers, increasing the complexity of the manufacturing process and reducing consistency in the final products. Image used courtesy of Stetron

 

Housholder shed light for us on the consistency benefits of solid-state speakers. “In terms of loudness, in terms of phase matching, they’re now getting speakers that they no longer have to bin,” he said.

 

”They can take any two speakers off of a tape and reel out of a tray, throw them in left and right earbuds, and they’re going to be perfectly matched.”

 

At low frequencies, however, solid-state speakers cannot perform as well as their coil-and-magnet counterparts due to their smaller size and inherent limitations. Using advanced techniques like sound from ultrasound, however, xMEMS has produced a solid-state speaker that can directly compete with traditional speakers in a variety of applications.

 

Coherent Sound with Modulation

Instead of creating the sound waves directly, by pushing and pulling the air at the audio frequency, the Cypress speaker leverages ultrasonic pulses in order to encode the audio signal. Using a companion chip called Alta, audio is encoded in the amplitude of ultrasonic pulses, which can then be demodulated by piezoelectric valves.

This system allows the Cypress speaker to produce high-fidelity and powerful low-frequency sounds by combining multiple high-frequency pulses, removing a major limitation of solid-state speakers.

For applications such as adaptive noise canceling, the target sound pressure level (SPL) is typically +140 dB to account for low-frequency leakage. Previous generations of xMEMS speakers have reported 120 dB at 200 Hz and 110 dB at 1 kHz, but still rely on other sources such as coil-driven speakers to cancel low-frequency noise.

Cypress, on the other hand, doesn’t require any other source in order to produce the required SPL at low frequencies. Thanks to the sound from ultrasound technology, Cypress speakers are able to produce over 140 dB at frequencies as low as 20 Hz, making Cypress a good candidate for an all-in-one noise cancellation solution that can compensate for even the loudest noise sources.

 

In the Cypress speaker, ultrasonic pulses encode the audio signal, while piezoelectric valves demodulate the audio signal to produce a flat response across the entire audio range. Image used courtesy of xMEMS

 

When discussing the potential of xMEMS’ latest chip to change how designers make sound and the improved low-frequency performance, Housholder said, “That’s what Cypress is meant to do. Get you back to just a single thin speaker that can do everything. So, to get that, Cypress now represents about a 40× increase in low-frequency energy compared to our prior generation products. That’s a huge leap.”

Full-function Cypress silicon is now sampling to select customers, with mass production planned for late 2024. For interested designers, however, xMEMS will be demonstrating Cypress by appointment at CES 2024. 

 

Moving to Solid State

While solid-state technology likely won’t replace coil-driven speakers entirely, the addition of thin, lightweight, and powerful speaker technology that relies less on moving parts is certainly a benefit to designers and audiophiles alike.

As designers begin experimenting with technology like Cypress, it will be exciting to see how adjacent fields such as audio processing and high-fidelity audio adjust to the new levels of control and performance afforded by the move to solid-state.

 

As MEMS technology evolves, solid-state speakers are beginning to act as a full replacement for traditional coil-driven speakers, giving designers more performance in a smaller package. Image used courtesy of xMEMS

 

Despite where Cypress finds itself in the next few years, xMEMS feels that the availability of Cypress may mark a paradigm shift in the audio field, according to Housholder.

 

“This is a true solid-state alternative to, really, the highest volume segment of the personal audio market. So we’re really excited about this.”

 

And, if solid-state speakers become the new norm, designers and consumers alike should share in the excitement.