Monolithic MEMS drivers are already recognized for its clear benefits, and specified for new high performance in-ear designs, even though the very high SPL levels required on the critical bass frequencies for active noise cancellation (ANC) applications has required designers to specify a hybrid solution. As noted by experienced ODMs such as Bujeon Electronics, using a dynamic driver to complement the xMEMS Cowell tweeter, as an example, provides a "drop-in" solution compatible with today’s leading TWS system-on-chips.
Not resting on its laurels, xMEMS now designed a solution that provides effective ANC from a single MEMS microspeaker, in order to actually meet all current applications and market requirements, including adaptive noise cancellation and enhancement. xMEMS has reported positive progress on a new development that will make this possible, scheduled to appear already in 2024.
According to the company, for the new Cypress solid-state MEMS speaker, xMEMS engineers have replaced push-air sound reproduction with an ultrasonic amplitude modulation transduction principle. This allows the new Cypress solid-state, all-silicon microspeaker to achieve >140dB low frequency sound pressure level (SPL at 20Hz, measured in a standard IEC60318-4 ear simulator), enabling a no-compromise replacement for conventional voice coil drivers in noise canceling earbuds. This is a revolutionary breakthrough in sound reproduction, promising to change the mass-market for true wireless stereo (TWS) earbuds.
"Sound from ultrasound has been a research topic since the 1960s but has never achieved the acoustic performance required for broad commercial appeal, until Cypress. By shifting to a sound from ultrasound principle, the xMEMS Cypress microspeaker can now officially replace traditional coil-and-magnet speakers in active noise canceling earbuds," says Mike Housholder, Vice President, Marketing & Business Development for xMEMS. "Cypress maintains all of the benefits of xMEMS' existing speakers, while being 40x louder in low frequencies, achieving a key requirement for ANC earbuds."
Explaining how the Cypress is able to achieve this performance, xMEMS says that Cypress takes advantage of the characteristics unique to MEMS — speed, precision, and uniformity. Instead of generating sound in the audible band, the new Cypress driver acts as an air pulse generator and generates an amplitude-modulated ultrasonic wave (carrier) that faithfully follows the amplitude of the intended audio signal. This modulation stage is complemented with a demodulator that synchronously demodulates the ultrasonic wave, transferring the acoustic energy down to the baseband, producing the intended audible sound as a result.
"The sound envelope of ultrasonic pulses is an exact acoustic copy of the source signal, meaning across all frequencies, Cypress is more faithful to the original recording than current speaker technologies. As a result of its superior resolution in the time domain, Cypress can more accurately reproduce today’s advanced sound formats, including high-resolution and spatial audio. Cypress not only revolutionizes how sound can be reproduced from an electric signal, but it also redefines how it should be reproduced," says Jemm Liang, xMEMS CTO.
For this new development, xMEMS leverages the same production-proven MEMS platform used for all its existing products and exploits all the benefits of xMEMS’ established solid-state speaker designs when compared to legacy coil architectures, including faster mechanical response, near-zero phase shift, and superior part-to-part consistency. Rigid silicon diaphragms eliminate speaker breakup for unmatched mid/treble clarity, and are also non-magnetic, enabling lower weight designs and reduced electromagnetic interference.
Using a solid-state semiconductor process, xMEMS is able to offer superior quality, reliability, and part-to-part uniformity in all its designs. Cypress will be available originally in a 6.3 x 6.5 x 1.65mm package (9mm-diagonal), providing a bass response that is consistent with the best 10-12mm legacy coil speakers with even greater sound pressure levels (SPL).
This additional low frequency SPL is most critical for ANC earbuds. With Cypress, xMEMS brings unique advantages over legacy coil to further improve ANC applications. The device's faster electrical-to-acoustic conversion can contribute to wider ANC bandwidth (i.e., extension of ANC to cancel higher frequency noise sources, like a crying baby). Plus, Cypress’ near-constant electrical-to-acoustic conversion time (group delay), can reduce DSP filter complexity which, in turn, leads to shorter DSP latency, rounding errors, and power consumption when processing ANC.
Full-function Cypress prototype silicon is now sampling to select early customers. Production-candidate samples of Cypress and the companion Alta controller/amplifier ASIC will sample in June 2024. Mass production is planned for late-2024.
xMEMS will demonstrate Cypress by appointment only, January 9-12 at CES 2024 in Las Vegas, NV.
www.xmems.com
