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What Are the Advantages of MEMS Loudspeakers

By USound

MEMS-based loudspeakers are a new technology that challenges the status quo of electrodynamic and balanced-armature speakers. A frequently asked question is, how are MEMS speakers better? This article strives to answer this question.

First of all, the general advantages have to be separated from application-specific advantages.

The general advantages of MEMS loudspeakers are:

  • Seamless integration in an electronic PCB; in fact, the speaker itself is built on a PCB substrate. The speakers can be easily integrated in a PCB with the electronics of wireless earbuds, headphones, wearables, etc.

Image of MEMS-based speakers are built on PCB substrateFigure 1: MEMS-based speakers are built on PCB substrate. (Image source: USound)

  • Integration of the amplifier and of the MEMS speaker on the same PCB substrate. USound provides audio modules with analog and digital interfaces; this dramatically shortens the times needed to design audio products. The audio modules include programmable filters that can be changed to easily tune the audio. The firmware delivered with the audio module includes different sets of filters that pre-considers several use cases.

Image of Usound integrates the amplifier and MEMS speaker on the same PCB substrateFigure 2: USound integrates the amplifier and MEMS speaker on the same PCB substrate. (Image source: USound)

  • Lower power consumption. Despite the fact that MEMS speakers require higher voltage levels compared to electrodynamic speakers, the overall power consumption is lower. The MEMS speaker, due to the own intrinsic high impedance, demands a lower driving current. Table 1 shows the driving current of the MEMS speaker measured in an IEC coupler at 94 dB SPL using three different methods. Also included is the current consumption of a reference balanced armature (Knowles 26824) and electrodynamic speakers (Samsung HS330).
Measurement
USound Ganymede (MEMS)
Current Consumption (mA)
IEC 60268-1 0.28
Pink Noise 0.57
1 kHz Signal 0.11
Measurement
Knowles 26824 (BA)
Current Consumption (mA)
IEC 60268-1 0.46
Pink Noise 0.76
1 kHz Signal 0.33
Measurement
Samsung HS330 (ED)
Current Consumption (mA)
IEC 60268-1 1.43
Pink Noise 1.84
1 kHz Signal 1.92

Table 1: The USound MEMS speaker driving current measured at 94 dB SPL using three different methods and compared to a Knowles 26824 reference balanced armature and Samsung HS330 electrodynamic speakers.

The low current consumption makes the MEMS speaker the perfect companion for all audio wireless applications like true wireless earbuds.

The power consumption of MEMS speakers can be further reduced, taking advantage of their capacitive load. Electrically, MEMS speakers behave like capacitors, therefore the main portion of power is reactive and can be re-used in the system. USound’s new digital power amplifier can recover a significant percentage of the reactive power.

Knowles 26824 Samsung HS330 Ganymede
Active Power 50.5% 89.9% 7.0%
Reactive Power 49.5% 10.1% 93%

Table 2: A comparison of active and real power ratios for Knowles speakers, Samsung headset, and USound MEMS speakers.

Application-specific advantages

The application-specific advantages must be separated into two main kinds of applications:

  • Occluded-ear applications, where the speaker, mounted in an earbud, sits inside the ear canal. In this kind of application, the ear exclusively captures the sound emitted by the loudspeaker; external sounds are attenuated by the sealing of the earbud.
  • Free-field applications, where the speaker is placed outside the ear and the ear is free to capture sound coming from additional sources other than the loudspeaker itself.

Advantages for occluded-ear applications

The main advantage is the overall small form factor. This considers the dimension of the loudspeaker and of the back and front volume that, with the MEMS speaker, can be kept to the minimum. Figure 3 shows the ear tips of the Megaclite reference design for USB-C earbuds.

Combining the low power consumption with the small overall form factor showcases the main advantage for wireless earbuds: the small form factor allows the usage of larger batteries and the lower power consumption drain less current from the battery, resulting in an overall extended battery life.

Diagram of USound’s Megaclite reference design USB-C earbudsFigure 3: USound’s Megaclite reference design USB-C earbuds. (Image source: USound)

USound’s single-driver MEMS speaker has a large bandwidth. Figure 4 shows a test report made by a major Chinese audio company that compares USound MEMS-based earbuds with two top-notch brands. The results clearly show that a single MEMS driver can easily compete with an electrodynamic and multi-driver balanced armature configuration. This makes the MEMS speaker a compelling technology for true-wireless earbuds. The combination of low power consumption, small form factor, and the widest possible bandwidth provides unprecedented advantages for true wireless manufacturers and end-users.

Graphs of bandwidth comparison between balanced armature (BA), MEMS, and electrodynamic speakersFigure 4: Bandwidth comparison between balanced armature (BA), MEMS, and electrodynamic speakers. (Image source: USound)

Advantages for free-field applications

For free-field applications, the small form factor is not suitable for full-bandwidth applications. Nonetheless, MEMS speakers offer unique advantages as a high-quality tweeter with extended bandwidth in the ultrasonic region (up to 80 kHz).

The small form factor is suitable for all kinds of wearable applications. In 2019, USound started marketing an audio module for AR/VR glasses that includes a fully digital audio system. This system includes an electrodynamic woofer and a MEMS tweeter. It provides, compared to single-driver systems, much brighter sound and a unique feature that focuses the sound around the user's ears and attenuates the level of the audio signal even at a very short distance from the ear, guaranteeing a good degree of privacy.

Diagram of USound’s audio module for AR/VR glasses includes a fully digital audio systemFigure 5: USound’s audio module for AR/VR glasses includes a fully digital audio system. (Image source: USound)

Another application that takes advantage of the thin form factor of MEMS speakers lies in arrays, e.g., in automotive sound systems. A modular array such as USound’s reference design Harpalyke can be mounted directly in the car ceiling, removing often bulky and heavy tweeters from the car. Not only does the MEMS audio system reduce weight and free space in the car, but the audio is often a crisper and brighter quality, thus providing a unique listening experience.

Image of MEMS speakers’ thin form factorFigure 6: MEMS speakers’ thin form factor is ideal for speaker arrays such as those in infotainment systems in automobiles. (Image source: USound)

Final thoughts

MEMS speakers are a new technology and their full potential will be revealed step by step. Already, this technology provides unique features and compelling advantages compared to electrodynamic and balanced armature speakers. In the fast-evolving audio market, early adopters of MEMS technology can provide unbeatable advantages to their end-users.

Finally, designers can get a first-hand feel for the capabilities of MEMS speakers and explore their potential applications by using Digi-Key’s exclusive USound MEMS speaker and test board evaluation kit.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

USound

USound is a fabless audio company offering high-performance silicon speakers and high-quality sound solutions based on MEMS (Micro-Electro-Mechanical Systems) technology, safeguarded by over 150 filed patents. With its offices in Graz, Vienna, San Francisco, Shanghai and Shenzhen, USound serves international customers, enabling them to create totally new smart audio applications with MEMS speakers. USound's products are designed to fit seamlessly into earphones, headphones, wearables, and smartphones. With the introduction of innovative MEMS technology, USound is setting new standards in terms of audio experience and low power consumption.