Servo-Control in Mainstream Audio: From Motional Feedback to the Bend-Sensor

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.

In this final article of the four-part series, Andy Lewis expands upon the Back EMF concepts hinted at in the previous three articles in this series. This article explores the Electrical and Newtonian filters and their intersections, observations on reactive parallel filters as pertains to Back EMF and energy losses. The theories can be applied to virtually all areas of loudspeaker design. This article was originally published in audioXpress, November 2018.

In the third article of the four-part series, Andy Lewis continues his fascinating exploration of Back EMF Phase Relationships in Moving-Coil Loudspeakers. The author discusses what causes Back EMF to simulate inductor, capacitor, or resistor (LCR) components, and explores the concept of slip, in order to explain how and why it causes the impedance to be inductive, resistive, or capacitive, depending on frequency. This article was originally published in audioXpress, July 2018

In this article series, Andy Lewis explores the generation of Back EMF in the region of a loudspeaker’s resonance. In this second article of the four-part series, he performs simple “thought experiments” to make qualitative observations about the activity of a moving-coil driver in the region of its resonance. This article was originally published in audioXpress, June 2018

In this article, Andy Lewis explores the generation of Back EMF in the region of a loudspeaker’s resonance. He also demonstrates a method for calculating the position of the moving assembly (or “cone”) relative to input signal, using complex impedance measurements. This article - part of a four part series - was originally published in audioXpress, May 2018

audioXpress July 2018 is one of those editions that we are certain our readers will read, revisit, and keep for reference again and again. Start with the Editor's notes about the search for a sound reference standard, read our review of Sonarworks Studio Monitor and Headphone Calibration Solution, Reference 4, and learn more about microphone choices. Next up, we interview the new owners of Creative Sound Solutions, a DIY-oriented company, and we follow up with the AXPONA 2018 show report. Gerhard Haas concludes his series on audio transformers for tube amplifiers, and Andy Lewis continues his fascinating exploration of Back EMF.

The June 2018 edition of audioXpress is now available. In this edition, read how MPEG-H audio is introducing new dimensions to television sound, how to deal with mixing and mastering music for music streaming services, and how to design new voice-enabled smart gadgets. You can also build a turntable speed measurement device, and learn more about MQA streaming. And be sure to read the interview with Robert Oliveira, the founder of Comply Foam. Get your issue now.

The May edition of audioXpress continues to be a favorite among tube and audio electronics aficionados. For this Glass Audio Special issue, Menno van der Veen, details his fifth 300B-SE amplifier, Patrick Brunner discusses DIY Tube Amp Heat Management, and Gerhard Haas shares what he knows about output transformers for tube amplifiers. We interviewed Jason Stoddard, the heart and mind of Schiit Audio, and Richard Honeycutt compares Tubes, FET, and BJT circuits. Also in this edition, Andy Lewis looks at Back EMF in loudspeakers, and Ron Tipton finds a way to measure the high-frequency content of Master Quality Authenticated (MQA) recordings. Download your May issue now.