For the past 100 years or so, the audio industry has been using coil-based driver technology for its loudspeakers. Although the technology has several disadvantages, it has dominated the landscape for so long simply because of the absence of a suitable alternative cost-effective technology. Now, this is likely to change, at least for the next generation of earbuds using micro speakers. A new startup, the CA-based firm xMEMS, has been perfecting its MEMS driver.
The company has created three MEMS or micro-electro-mechanical-systems micro speakers, suitable for use in hearing aids, wired and wireless earbuds, smart glasses, loudspeaker tweeter arrays, and virtual reality headsets.
xMEMS is promising a long list of advantages for its solid-state micro speakers. For starters, the driver is only about 1 mm (1/25th of an inch) thick. That leaves more room for sensors, batteries, and other components. The entire speaker is made of silicon, including the actuator and membrane. This eliminates the need for matching the driver and calibrating it. Being entirely solid-state, the MEMS technology allows mass production of the high-resolution capable micro speaker in more precise configurations than is possible with traditional designs. It does not involve the tedious manual assembly of balanced-armature drivers, as in regular coil-based speakers.
The solid-state micro speakers boast a flat frequency response for the full audio spectrum ranging from 20 Hz to 20 kHz. While there are no in-band resonances, these speakers exhibit an astonishing ±1° phase consistency for spatial performance. As the MEMS speakers show a superior high-frequency response in comparison to coil speakers, their clarity and presence are outstanding. The high-speed mechanical response results in a group delay of less than 50µs, while their total harmonic distortion is only about 0.5% or 94dB at 1kHz. The near-zero phase delay results in improved noise suppression.
In addition to the superior performance characteristics above, the new MEMS speakers can withstand mechanical shock to a greater extent than their coil-based counterparts can. This is due to their monolithic design, eliminating the spring and suspense structure of coil-based speakers. Being totally solid-state, the new speakers consume far less power for the same output, thereby improving battery life. No added membrane is necessary for resistance to dust and moisture up to IP58.
In a blog, xMEMS claimed their MEMS speakers are suitable for high-resolution audio. Although for high-resolution audio, the focus is more on the codec’s ability to achieve suitable bit depth and sampling rates, requirements from the speaker are just as stringent.
Typically, the digital signal chain and the codec are responsible for the highest quality of data stream. Since the speaker is the ultimate transducer for the sound that people hear, it must accurately render and reproduce the sound as the artist intended.
In this respect, the performance of solid-state MEMS micro speakers suits the standard requirements significantly better than coil-based speakers can. The MEMS speaker’s extended bandwidth and its mechanical and ultrasonic near-flat response above 20 kHz are responsible for that.
The MEMS driver works on the principles of inverse piezoelectric effect. The application of voltage causes the actuator to contract and expand, converting electrical energy into mechanical sound energy.
