tws earbuds


Advantages of MEMS Speakers in True Wireless Stereo (TWS)

USound MEMS speakers provide unique features and compelling advantages compared to electrodynamic and balanced armature speakers. The application-specific benefits of MEMS speakers must be separated into two main kinds of applications: free field and occluded ear applications. In this article, we will focus on the latter.

Occluded ear applications

When we talk about occluded ear applications, we refer to audio systems in which the speaker, mounted in an earbud, sits inside or at the entrance of the ear canal. The air volume between the speaker and the eardrum is isolated from the outside by using a sealing ear tip, typically made from silicone. In this kind of application, the ear can exclusively capture the sound emitted by the loudspeaker; the earbud’s sealing attenuates external sounds.

True wireless earbuds

True wireless earbuds have been dominating the market since the launch of the Apple AirPods in 2016. As several brands already jumped on the TWS trend, differentiation is critical to stand out. TWS is the predominant choice among consumers because of its portability, form factor, and freedom of movement they provide.

Manufacturers are looking for ways of enhancing the user experience of TWS — either by improving the sound quality, the noise-cancelling capabilities, the battery lifetime, adding sensor functions, adding connection via NFC, or improving the design and ergonomics.

Advantages of USound MEMS speakers in occluded ear applications

The main advantage that USound MEMS speakers offer in this setting is the overall small form factor. It is the thinnest MEMS speaker available on the market. This includes the dimension of the loudspeaker and the back and front volume. Both, thanks to the MEMS technology, can be kept to a minimum without degrading the acoustical performance.

The image below shows how little space a MEMS loudspeaker (right side) takes up compared to a traditional 6 mm electrodynamic loudspeaker (left side) commonly used in today’s TWS earbuds.

A further advantage is the wider acoustical bandwidth that a single USound MEMS speaker can achieve. Due to the low moving mass, the upper end of the bandwidth is limited solely by the acoustic mechanical design and not the speakers themselves. See below a comparison of the SPL between an earbud containing a single MEMS loudspeaker with an earphone containing a high-end electro-dynamic (ED) loudspeaker and an earphone containing three balanced armature (BA) speakers. As shown, a single MEMS loudspeaker can reproduce a higher bandwidth (higher SPL at the high frequencies) than a BA based earphone, even when using multiple BA speakers, while maintaining a more natural upper-midrange than the ED-speaker earphone.

As a general reference, the Harman In-ear target is added in the background. This represents the most commonly accepted target frequency shape an ideal in-ear phone should have. USound deviates from this slightly on purpose, based on our own research.

Harmann target for in ear and USound MEMS speakers

The results clearly show that a single USound MEMS speaker can easily compete with even a multi-driver balanced armature configuration. This makes the MEMS speaker a compelling technology, especially for TWS-earbuds, where there is no space for multiple BA speakers.

USound’s philosophy is to supply our customers not only with the MEMS speakers but to offer in-depth support on the acoustic and electronic side if desired. Since MEMS speakers require a different electrical driving stage than electro-dynamic speakers, USound also assists by providing reference designs. USound team developed and delivered to the market ASIC linear audio amplifier Tarvos. It is a dedicated amplifier to drive USound MEMS speakers optimally and power-efficiently. With this, we can also guarantee an optimized audio signal chain from the Bluetooth receiver to the listener’s ears. Additionally, one of upcoming products in USound roadmap will contain these signal blocks — ASIC, MEMS speaker, and acoustic design, within one integrated audio module Kore, which can then be used as an all-in-one audio solution for TWS.

In summary, the combination of a small form factor and the wide bandwidth provides unprecedented advantages for true wireless manufacturers and end-users when using USound MEMS speakers.

Contact us to learn more about which MEMS speakers version is more suitable for your target specifications.

Contact sales now >

About the author

Jakob Spötl works as head of acoustics in the R&D department of USound. Before joining USound in 2015, he finished his studies of electrical and audio engineering at the TU Graz. LinkedIn