Speakers are traditionally not part of our coverage, but everyone should be aware of today’s announcement of xMEMS ‘new speaker technology. Voice coil speakers as we know them and which have been in one form or another for over a hundred years have been the basis for how we experience audio playback.
In the past few years, semiconductor manufacturing has become established and has become more accessible. MEMS technology (Microelectromechanical Systems) is now so advanced that we can develop speakers with properties that are fundamentally different from conventional dynamic drivers or symmetrical armature units. The “Montara” design by xMEMS promises to be exactly this alternative.
xMEMS is a new start-up founded in 2017 with headquarters in Santa Clara, CA and a branch in Taiwan. So far, the company has been in stealth mode and has not released any product publicly to date. The company’s motivation is to overcome decades-old barriers in loudspeaker technology and to reinvent the sound with new innovative solutions made of pure silicon. Extensive experience is used here, which the founders have accumulated in various MEMS design houses over the years.
The manufacture of the pure silicon speaker from xMEMS is very different from that of a conventional speaker. Because the speaker is essentially just a monolithic piece made using your typical lithography manufacturing process, similar to other silicon chips. Because of this monolithic design aspect, the production line is significantly less complex than voice coil designs with a variety of components that need to be assembled precisely – a task that is said to require thousands of factory workers.
The company did not want to disclose the actual process node of the design, but expected something quite coarse in the micrometer range – it only confirmed that it was a 200 mm wafer technology.
In addition to simplifying the production line, another great advantage of the lithographic aspect of a MEMS speaker is that its manufacturing precision and repeatability are significantly superior to that of a more variable voice coil design. The mechanical aspects of the design also have crucial advantages, such as a membrane movement with a higher consistency, which enables a higher reactivity and a lower THD for active noise suppression.
The Montara design from xMEMS consists of an 8.4 x 6.06 mm silicon chip (50.9 mm²) with 6 so-called loudspeaker cells – the individual loudspeaker MEMS elements that are repeated over the chip. The frequency response of the loudspeaker covers the entire range from 10 Hz to 20 kHz. This is a problem with current dynamic or symmetrical armature drivers and why several such speakers are used to cover different parts of the frequency range.
The design is said to have extremely good distortion properties, can compete with planar magnetic designs and promise only 0.5% THD at 200 Hz – 20 kHz.
Because these speakers are capacitively piezo and current controlled, they can reduce power consumption to a fraction of a typical voice coil driver and only consume up to 42 µW of power.
The size is also a major advantage of the new technology. XMEMS is currently producing a standard packaging solution in which the clay comes out of the packaging vertically and has the above-mentioned area of 8.4 x 6.05 x 0.985 mm. However, we will also see a side-firing solution with the same dimensions, but which allows manufacturers to better manage the internal headphone design and component positioning.
In the rough 3D printing unit mentioned above without any optimization in terms of sound design, xMEMS easily managed to design headphones with dimensions similar to the current standard designs. In fact, commercial products are likely to look much better and take better advantage of the size and volume savings that such a design would allow.
An essential aspect of the capacitive piezo drive is that a different amplifier design than that of classic loudspeakers is required. Montara can operate with up to 30 V peak-to-peak signals, which is far beyond the range of your existing amplifier designs. Customers who want to use a MEMS speaker design like the Montara need an additional companion chip like the LM48580 from Texas Instruments.
In my view, this is one of the major hurdles to broader acceptance of the technology, as its use is limited to more integrated solutions that actually offer the right amplifier design for driving the speakers – many existing audio solutions are needed. An additional adapter / amplifier if A manufacturer actually chooses a non-integrated “stupid” headphone design (like your classic 3.5mm earphones / headphones).
True Wireless Stereo (TWS) headphones are obviously the main target market for the Montara, as the amplifier aspect can be taken into account in the design and such products can take full advantage of the size, weight and performance of the new speaker technology.
When measured using the rough 3D printed headphone prototype shown above, xMEMS shows that the Montara MEMS speaker has a significantly higher sound pressure than any other headphone solution, with the production models fully achieving the targeted sound pressure of 115 dB (the prototype had only 5 of the 6 cells) active). The native frequency response is much higher here at the higher frequencies. This enables providers to adapt and filter the sound signature in their designs. Filtering down is much easier than boosting at these frequencies.
THD at 94 dB SPL is also significantly better than even an unnamed pair of professional $ 900 IEMs – and it is reiterated that this is just a rough design without any audio optimizations.
In terms of cost, xMEMS did not provide an exact number, but informed us that it will be in the range of current designs with balanced anchors. The Montara speaker from xMEMS is now being tested by vendors. The expected mass production is expected to start in spring next year. Commercial devices from suppliers should also see the light of day at this time.