I’ve been around audio and computer technology long enough to have seen many “next big things” or interesting concept transitions into real world products. After spending some quality demo time with the xMEMS company and their silicon micro-speaker, I can say that this concept has the potential to deliver audiophile-quality earbuds at very consumer-friendly prices.
xMEMS derives its name from MEMS (micro-electro-mechanical systems), a technology that includes both electronics and mechanical elements at a microscopic level. MEMS are already used in a host of applications, including tiny microphones; my xMEMS demo was related to using MEMS to build high-quality but low-cost audio products, including earbuds.
The company’s micro-speakers are silicon chips with piezoelectric flaps mounted on top that rapidly deform and relax when hit with transient electrical signals. The resulting vibration moves air, creating sound. Essentially, the silicon chip on which the micro-speaker is built performs the same task as a magnet would in a conventional speaker, and the flaps perform the role of a traditional speaker cone.
What are the specifications behind the technology of xMEMS
I was impressed with the specifications xMEMS touts even before I heard his demo: Flat frequency response from 20Hz to 20kHz–or higher, if you want it; lightning fast response and settling times (ie the speed at which a speaker starts and stops vibrating respectively); device resonance above 10kHz, where the effect is minimal, are all much better than the best specs I’ve seen for traditional audiophile speaker designs.
xMEMS’ Montara, Cowell, and Montara Plus microphones are manufactured on silicon wafers at TSMC’s factory at a cost per unit that should allow an earphone manufacturer to build an audiophile-quality product with retail prices in the $125 to $200 price range.
xMEMS says the sonic uniformity of a microscopic product produced on wafers saves vendors tons of money. Normally, speakers must be sorted according to their relative merits before they can be matched as stereo pairs. Non-uniformity in frequency response, resonance, and/or transient response can play havoc with a set of speakers’ fidelity.
MEMS micro-speakers also have other advantages: the absence of magnets means that speaker designers do not have to compensate for the interference produced by magnetic fields.
And xMEMS says its product is rated IP58 for protection against dust (particles will not cause failure) and water (they can be submerged in up to three meters of water for 30 minutes). And that is for the components themselves, even before they are put into an enclosure. So, if you forget to take your xMEMS-based earbuds out of your pocket before throwing your pants in the wash, you won’t regret that they’ve been destroyed after the spin cycle. Looking for more in-depth information about IP codes? Just click on the previous link.
xMEMS also produces a solid-state, dynamic (open/close by signal) physical shutter, called Skyline, which OEMs can use to exclude or admit ambient noise. The Skyline can enable more versatile, combination open-ear/closed-back headphone designs.
The last component I was shown was a small patch of an amplifier, the Aptos, which can be seen in the schematic below. That image also shows how xMEMS speakers can be combined with traditional audio speakers to increase bass response.
Today, xMEMS’ micro-speakers are designed only for captive-air (in this case, the space in your ear canal) audio devices such as earbuds and hearing aids; however, the company is working on a free-air design (essentially meaning no enclosure is required) that could be used in applications where more air must be moved, such as portable Bluetooth speakers or bookshelf speakers.
The xMEMS demo delivered impressive sound
The sonic quality I heard from xMEMS’ 3D printed earbuds prototype prove that the company’s specifications are not just empty numbers. The three things I look for when reviewing audio products—punchy bass, easily discernible and realistically rendered acoustic instruments, and accurate high-end frequencies with some sparkle, if you will—were all accounted for.
I put most of the credit for the tight bass and mid-range accuracy to the lightning-fast transient response and calculation times, but xMEMS also plays up the lack of phase distortion and, of course, the product’s super-high resonant frequency.
Note that I heard both the Montara Plus bare and the Cowell, the latter acting as a full-range speaker sitting atop a 9mm traditional speaker (shown above), where it provided additional thump and sub-bass.
I also checked the Skyline vent, which also worked as advertised. The incoming ambient sound had a blinding quality, but I think that was at least partially due to the housing of the 3D printed earbud.
The future of MEMS technology in speaker design
There are simply too many advantages, not the least of which are affordable retail products with incredibly accurate sound, for MEMS speakers not to have a major impact on the earbud market. I think audiophile earbud vendors will soon be crying into their beer about the arrival of cheap, high-quality sound for the masses. And for that I say “hard”.
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