R&D Stories: Motion Feedback for Active Desktop Subwoofers

Zami Schwartzman, the founder of Servobass, shares his journey into the application of Motion Feedback (MFB) methods for active subwoofers. He explores passive and active bass enhancement methods and how Servobass arrived at an optimized design using MFB techniques to achieve highly performing active subwoofers in desktop and compact sizes. A solution that is now available to be licensed by the industry. This article was originally published in audioXpress, November 2023.

The September 2022 Speaker Focus issue of audioXpress discusses speaker design and testing tools and features two fascinating speaker R&D stories on the Holoplot X1 Matrix Array and Motion Feedback Desktop Subwoofers for nearfield studio application. Geoff Hill explains the latest IEC loudspeaker measurement standards, Roger Shively reports from the AES 2022 Automotive Audio conference, Christoph Sladeczek writes about Audio Objects as Platform Technology in Vehicles, and much more.

In this article, James Croft looks at a patent awarded to David Russell (Toronto, CA); and John French (Caledon, East, CA) on behalf of Audera Acoustics, Inc., Schomberg CA. The patent describes a generic acoustic high displacement transducer system, containing a diaphragm position sensing module, a controller with a transmitter, so that the voice coil moves at least partially in response to the control signal.

Grimm Audio introduced the successor of its LS1s-DMF motional feedback subwoofer: the SB1. The new design takes Grimm's Digital Motional Feedback approach to a whole new level. The new subwoofer uses a new and improved driver, over which Grimm Audio could build a better electronics implementation and leverage significant evolution in sensors and DSP, creating an even better match for its LS1 series speakers.

As previously teased, KEF announced the launch of the new KC62 powered subwoofer with three innovative technologies that successfully prioritize design and sound in equal measure. Combining the brand's technologies and skills, KEF's engineers have developed a brand new approach to subwoofer performance, allowing maximum bass in a minimum space. Using KC62's force-canceling and Uni-Core technologies, KEF surpasses traditional expectations of what a subwoofer can achieve based on its size.

Imagine a new class of speaker diaphragm position sensors that enable audio engineers to reduce distortion and extend bass response from studio monitors, soundbars, smart speakers, and even smartphone microspeakers. With the precision of laser displacement instrumentation, this sensor is located between a stationary component of the speaker and an appropriate moving part to provide an error correction reference signal back to the amplifier. Well, that sensor has already been developed. ​This article was originally published in The Audio Voice weekly email newsletter.