Bass-Boosting Earbuds: Introducing the Ultrasonic Micromachine

XMems Labs Reveals Mems-Based Loudspeaker with Ultrasonics

XMems Labs has unveiled a groundbreaking mems-based loudspeaker that utilizes ultrasonics to reproduce bass notes. Branded as 'Cypress', this innovative technology is described by the company as "full-range" and is capable of achieving over 140dB low frequency SPL (sound pressure level), making it an uncompromising replacement for coil speakers in noise-cancelling earbuds.

In the design of an earbud, three key components are involved: a conventional wireless earbud receiver IC, a custom modulator IC (branded as 'Alta'), and the Cypress mems demodulator/transducer.

The modulator IC combines an ultrasonic carrier with the audio signal, generating two signals for the transducer: a 'side-band suppressed carrier' signal and a synchronized demodulation signal.

According to xMems, the side-band suppressed carrier is fed to the membrane actuators within the mems transducer (referred to as 'SM' in the diagram on the left), producing ultrasonic modulated pressure in the chamber. On the other hand, the synchronized demodulator signal is directed to the valve actuators (SV left), which demodulate the ultrasonic pressures to generate audio.

XMems has been relatively secretive about the details of this waveform, with only a few pieces of ultrasonic demodulation information released thus far. However, xMems claims that "the sound envelope of ultrasonic pulses is an exact acoustic copy of the source signal." Furthermore, they state that this technology is 40 times louder in low frequencies compared to xMems' previous generation speakers, with a sound pressure level greater than 140dB as low as 20Hz. This measurement is conducted using an IEC60318-4 ear simulator. Additionally, the near-constant electrical-to-acoustic group delay of the Cypress loudspeaker can reduce DSP filter complexity, resulting in shorter DSP latency and lower power consumption during active noise cancellation processing.

It is important to note that the 40x improvement claim is in comparison to xMems' 'Cowell' mems speaker, which is not their best existing low-frequency performer.

The total harmonic distortion from the new Cypress transducer and IC is reported to be less than 0.5% (111dB at 1kHz). The packaged mems measures 6.3 x 6.5 x 1.65mm (9mm diagonal, as shown in the application sketch on the left).

Currently, prototype silicon samples are being distributed to selected customers. Production-candidate samples of the mems transducer and companion modulator IC are scheduled for June 2024, with mass production expected to commence in late 2024. By appointment, the system will be demonstrated at CES (Las Vegas, 9-12 January).