The February 2025 issue of audioXpress reflects the cutting edge of audio product development. audioXpress recaps the fascinating world of microphone technology, where a lot has been happening, focusing on the latest in MEMS microphones. In “MEMS Microphones in the Age of AI,” J. Martins provides a unique overview of “the second coming for MEMS microphones.” As he explains, for more than 20 years, MEMS microphones have evolved to become the largest volume technology, even if they never overcame the technical limitations that would enable competing with established condenser, dynamic, and other microphone technologies. All that is now changing faster than we could envisage with new products, technologies, and new systems designed for the age of AI audio processing.In this Market Update on MEMS microphones, we learn about companies eager to enter the space with completely new technologies and technical approaches, not necessarily to compete with the low-price/large volume components but targeting new emerging markets and aiming to challenge even the more demanding professional applications.
Expanding on the microphone perspective, we move to the also fast-changing segment of wireless technology, with an article by Nick Wood from Shure: “Unlocking the Future of Wireless Audio: An In-Depth Look at WMAS.” Meeting the pressing needs for professional wireless microphone applications, struggling with RF challenges, regulatory constraints, and the scarcity of frequency spectrum, 2024 was the year of the first product announcements leveraging Wireless Multichannel Audio Systems (WMAS) technology. Sennheiser was the first company to unveil its ambitious bidirectional Sennheiser Spectera system using WMAS technology. Shortly after, Shure made its own announcement, and in this article Nick Wood provides a unique perspective of the WMAS technology, its future in the industry, and its regulatory framework for professional audio applications.
Next up, Philipp Paul Klose offers a unique insight into the future of microphone technology in his review of the Eigenmike em64, a sixth-order Ambisonics microphone with Dante connectivity, and extended with a comprehensive recording and decoding software suite from mh acoustics. With a spherical microphone array that contains 64 professional-grade omnidirectional electret microphones mounted on a rigid spherical baffle, mh acoustics updated its previous Eigenmike em32 model, bringing a state-of-the-art higher order Ambisonics capture tool to the market. The patented design combines microphone programmable gain preamplifiers, 24-bit A/D conversion and microphone calibration, all integrated. The Eigenmike em64 allows for tremendous degrees of freedom in projects requiring recording soundfields in any location. From acoustic measurements to 360° recording and complex soundfield analysis, the em64 enables multiple use cases, which are all explored in this article.
For this month’s Sound Control article, Richard Honeycutt explores how the earlier wisdom of Wallace Clement Sabine's equation and earlier calculations methods to estimate and tame reverberation time (RT) compare with computer model simulations and actual measurements. From RT to impulse responses (IR), and acoustical modeling software, this article explores in practice how calculations and predictions compare with current practices in architectural acoustics.
A second review included in this February 2025 issue is the eagerly awaited usage and measurements report of the Sony MDR-M1 Closed Monitor Professional Headphones by Brent Butterworth. Intended to become a new studio stalwart replacing Sony's MDR-7506 headphones, which have been a fixture in recording and radio studios for decades, the new MDR-M1 retails for two and a half times the price. What changed since the beloved 7506 appeared in the market was that headphones have become a larger volume category, and users are much more aware of these product’s failure points, such as non-detachable cables or headbands that wear out too quickly with use. Sony reviewed and improved upon all those aspects in the new MDR-M1 headphones and added a few improvements according to today’s high-resolution standards for mixing and mastering. Brent Butterworth shares everything he found and how the new model compares to the MDR-7506 classic and the AKG K371, currently a top competitor.
And this month’s deep dive into Development & Design comes from Alex Bonnet and Eric Benhaim, Orosound’s acoustics technical lead and chief technology officer, respectively. Titled, “Getting Out of the Ear: The Evolution of ANC Technology in Hearables,” this exclusive article from the French company leading in signal processing and edge AI noise-cancelling technology, offers a unique perspective of the challenges associated with the increasingly popular open form factors.
As a technology provider working with multiple brands on advancements in ANC technology for headphones and wireless earbuds, extensively familiar with product implementation challenges, the two authors address the specificities of loose-fit and open-ear designs — particularly regarding howling control. Going further, the article explains the potential of AI-based ANC technology for the future of hearables.
And moving on to DIY projects, audioXpress is privileged to publish a new project by Brian Lowe, of Belleson fame, detailing how he developed a unique custom designed transconductance amplifier (Top Amp) with fully differential (balanced) low noise JFET inputs and current output for phono preamps. Combined with a transimpedance amplifier, the Top Amp offers 50dB of current gain prior to any voltage excursion, virtually eliminating distortion caused by voltage dependent node capacitance exhibited by more conventional approaches. This article details the requirements and parameter values, while exploring design options. A second article next month will detail the discrete op-amp design, complete with simulations and measurements.
And expanding on last month’s article by Douglas Self, this issue completes the Modern Op-Amp Distortion Tests series with even more examples available in the market. Douglas Self has been using a tried-and-true palette of op-amps in his designs, but many new types have appeared in the last decade, and he thought it was time to evaluate those for distortion performance. In Part 1 of this article, he measured BJT-input devices. Here in Part 2, the measurement of BJT types is concluded, and then JFET types move to the test bench.
And this February 2025 issue closes with another journey to the tube classics. In his popular Hollow-State Electronics column, Richard Honeycutt writes about the legendary Dynaco ST-70 and ST-70 II tube power amps. A flagship product from a time when the build-it-yourself movement was in full swing, in 1959, Dynaco enticed audiophiles with its now legendary ST-70 amplifier, also sold as easy-to-assemble Dynakits. The success would be later expanded in 1992 with the updated and improved ST-70 II. The Dynaco ST-70 revealed an immense staying power that lasted until 2016 in its Series III form, offered by Radial Engineering, which acquired the Dynaco and Hafler brands in 2014.
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