The smallest loudspeakers in the world

13.8.2018

They are only a few millimeters in size and the perfect fit for headphones, hearables, and hearing aids: the world’s first integrated MEMS-based miniature loudspeakers. The loudspeakers are not only compact; they also offer impressive playback fidelity and low energy consumption. They were developed by Fraunhofer IDMT in Ilmenau and Fraunhofer ISIT in Itzehoe.

© Fraunhofer ISIT

The MEMS loudspeakers can be used for such applications as qualitative speech and music playback in headphones.

© Fraunhofer ISIT

Size comparison: The chip of a MEMS loudspeaker on a 20-cent coin.

With a membrane size of just 4 mm and a chip thickness of 0.4 mm, the fullrange loudspeakers cover the frequency range of 20 Hz to 40 kHz. When used in-ear, they achieve a sound pressure level of 110 dB. That is as loud as a rock concert. With reduced bandwidth, even up to 135 dB is possible.

Technological breakthrough in chip loudspeakers

The two Fraunhofer institutes have been working for three years on the joint research project “Smart Speaker – Smart MEMS Loudspeakers for Mobile Applications” developing energy-efficient and completely integratable loudspeakers on a chip basis: the Fraunhofer Institute for Silicon Technology ISIT is responsible for the development and pilot manufacture of piezoelectric microdrives as well as their integration into highly miniaturized intelligent microsystems. The Fraunhofer Institute for Digital Media Technology IDMT is concerned with the intelligent signal control of the miniature loudspeakers.

Positive resonance from industry

In March, the two research institutions presented their integrated MEMS loudspeaker technology in the form of an in-ear headphone at the annual conference of the German Acoustical Society (DEGA). They received very positive feedback from industry and science. “The punchy, balanced sound and the outstanding brilliance in the treble range were singled out for particular praise,” according to Fabian Stoppel, project manager and head of the group for acoustic MEMS at Fraunhofer ISIT. The coordinator of the overall project, Prof. Bernhard Wagner from Fraunhofer ISIT, is convinced of the high performance of the acoustic microsystems, confirmed by the positive feedback from industry representatives: “Our loudspeakers already fulfill many market requirements for hearing aids, in-ear headphones, and hearables. They can operate on only 1-2 V and have high power reserve levels”, Prof. Wagner is pleased to report.

What’s next? Adaptation for mass production, better performance, even lower energy consumption

The first success has been achieved. The institutes are currently working on optimizing the MEMS loudspeaker for deployment in in-ear headphones and devices with higher technological demands, such as cellphones, tablets, and laptops. “We have now reached a point where, from a technological point of view, the basic concept has been proved. Now we enter the optimization phase. Thanks to their intelligent actuation, in future, the loudspeakers will be able to offer long-term performance and sound quality in every application”, explains Dr. Daniel Beer, project manager at Fraunhofer IDMT.

At Fraunhofer ISIT, loudspeakers based on new piezoelectric materials are currently being developed, and they will be both compatible with CMOS and more energy-efficient. This will further reduce power consumption and will allow cost-effective mass production in all large semi-conductor factories. The institute is also working on further reducing the size, and therefore cost, of the miniature loudspeakers, which will open up new fields of application and make MEMS loudspeakers attractive for use even in the low-cost segment.