Measuring MEMS Microspeakers

Measuring MEMS microspeakers can be challenging due to their small form-factor, but it is increasingly important as they are now widely available and seeing fast evolution and adoption in true wireless stereo (TWS) earbuds and in-ear monitors (IEM). Accurate measurement is essential to understanding design considerations, as well as ensure product quality. In this article, published in the June 2024 issue of AudioXpress, Steve Temme and Michael Ricci (xMEMS) discuss the challenges of measuring fully piezoelectric MEMS microspeakers and demonstrate how SoundCheck reveals valuable distortion data.

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Introduction to Measuring MEMS Microspeakers Article

Measuring MEMS microspeakers - image of AX articleMEMS microspeakers are driving one of the fastest technological transitions in the miniature speaker market. MEMS transducers first gained widespread attention in the late 2000s with the first commercially available MEMS microphone, and over the course of a decade, they replaced electret microphones in the majority of mobile devices. The MEMS speaker revolution is shaping up for an even faster transition.

Early speakers incorporating MEMS technology were launched in 2014, but it was not until 2021 that the first fully piezoelectric MEMS microspeakers became commercially available. Manufacturers are already rapidly adopting these into TWS and pro-audio IEMs, earning praise from consumers and product reviewers alike, and propelling this technology into the mainstream.

MEMS Speaker Overview
MEMS microspeakers are constructed in an entirely different way from conventional miniature speakers. Rather than using inductive coils and magnets, they rely on a voltage-driven capacitive actuator, and they are entirely manufactured using a monolithic solid-state fabrication process in a semiconductor wafer foundry. This fabrication process delivers much tighter speaker-to-speaker consistency than is possible with a conventional driver made up of an assembly of many moving parts. They offer full-range performance, eliminating crossover networks that introduce complexity and sometimes even phase differences. This is particularly important considering this year’s other big audio trend—spatial audio, where the phase response is critical to accurate reproduction. Piezo-MEMS speakers are also compact in size and low power, making them economical on both space and power consumption. Finally, they are surface-mount technology (SMT) reflowable, offering yield and quality advantages in device manufacturing.

MEMS microspeakers are now commercially available and seeing fast evolution and adoption in true wireless stereo (TWS) earbuds and in-ear monitors (IEM). With the emergence of these small form-factor transducers comes the need to address how to measure its performance and ensure product quality.

While these advantages are leading to rapid adoption in devices such as hearing aids, earbuds, professional in-ear monitors, smart glasses, and more, they are not without their challenges. The
maximum sound pressure level (SPL) in the low frequencies is typically less than is required for a leak-tolerant active noise cancelling (ANC) system compared with conventional headphone drivers, limiting their use for ANC earbuds to a mid/high frequency tweeter in a two-way configuration. However, in recent months, manufacturers have made rapid progress in overcoming these
limitations, thus broadening their applications. For example, xMEMS’ new Cypress Piezo-MEMS speaker, showcased at the recent Consumer Electronics Show (CES), delivers up to 140dB SPL in the low-frequency band—more than sufficient for ANC applications.

The cost of MEMS-driven products is also decreasing as this technology is more widely adopted. While early MEMS earbuds were priced well over $1000, recently launched models such as the Creative Labs Aurvana bring this technology’s high-quality sound to TWS products below a $200 price point. As this technology moves toward becoming the de facto standard, the outlook for this market is positive.

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