As promised for this April 2025 issue, audioXpress features a comprehensive and highly valuable report on Wireless Earbuds and Hearables design, including the latest on the role of AI, sensors, and next steps in personal wireless. As J. Martins details examples of cutting-edge products, technologies, and trends in this space, you can read about how Bluetooth LE Audio and Auracast are holding product management decisions and calendars, while the industry tries to understand what will be Apple's next steps following a bunch of surprising announcements that caught all other players off guard. The report discusses health applications and the role of new advanced sensors, while exploring new AI-assisted concepts. New open-ear trends, technology partnerships, and the integrated platform approaches explored by companies such as Sonical and Bragi are also detailed in this Market Update.The issue also looks at a new opportunity in wireless headphones, which is starting to be explored by brands in the high-end segment. Providing a valuable Development & Design perspective, Christoph Apel (StreamUnlimited Engineering) writes about Wi-Fi Streaming for High-End Headphones. As a leading developer in the audio streaming sector, StreamUnlimited recognized this trend and developed an innovative Wi-Fi solution tailored to set a new level of seamless audio experience, with support for hi-res audio well beyond the limits of Bluetooth and introduces a new product segment in the headphone market, offering direct access to advanced streaming services.
In his regular Sound Control column, Richard Honeycutt expands on his personal journey building speaker systems, which he started to describe in the previous month, sparked by a magazine article detailing one way to minimize speaker cabinet-wall vibration by using a sandwich construction. Experiments from early speaker designs, such as building cabinet walls that helped to damp panel resonances and its effects, remain valid guidelines, as he embarked on a lifelong interest in designing and building custom speaker systems for schools, auditoriums, and churches.
The next article is one of those reference readings that reflects René Christensen's unique ability to clarify underlying problems before trying to engineer broader-level solutions. In "Acoustical Engineering via Various Expansion Techniques," he explains how when dealing with design decisions in acoustics, one should consider analytical approaches. For many problems, he suggests, one can synthesize a solution directly via an analytical modeling setup, which is superior to a numerical approach when it comes to calculation speed, gathering insights into the physics, and how they can be combined with numerical simulations to get the best of both worlds. The techniques shown in this article are some of the so-called “Expansion Techniques” with a focus on circuit implementations of physical problems in microacoustics and electromagnetics. A great read.
And from analytical modeling, we transition to a friendly analog domain with another great electronics DIY from audio expert Ethan Winer. This time he proposes one of many DIY examples from his upcoming Audio Circuits Cookbook, an excellent way to dive into the art of guitar effects and tone shaping, benefiting from the experience of someone who's been doing this since the 1960s. This article shows how to rewire a typical guitar using a Fender Telecaster as the example, and how to build small high-gain circuits like a fuzz-tone or compressor, to great effect.
For the next DIY article in this issue, you will need a bit more knowledge and patience, but we have no doubt that it will be a highly valuable learning exercise. The project was written by Vincent Thiernesse, a physics teacher and an experienced audio electronics practitioner. A true Renaissance man, the author has demonstrated a unique ability to reinvent concepts from scratch as he builds his own highly sophisticated measuring devices to serve his specific needs. For this project, he describes a Low Frequency Hybrid Crossover Filter, also defined as a Pseudo-Numerical and Switched Capacitor Filter, born out of a simple idea of changing the crossover frequency with a single control for his two-way system. Mixing digital and analog techniques for his design, this is a really interesting project to also learn the basics of signal processing.
Next up, we have A Primer on Class-D Amplifiers by Paul Marchese. There are many issues in the successful design of high-performance Class-D amplifiers that are unfamiliar to audio designers, and this detailed primer tries to rectify that. Starting with a detailed theoretical review of the Class-D concept in this article, which will be followed by a practical implementation, with an actual build using a familiar Texas Instruments TPA3255 integrated amplifier as a reference. This is a great audio electronics exploration of a valuable topic.
And finally, in his Hollow-State Electronics column, Richard Honeycutt writes about the fascinating story of Silvertone, the famous Sears house brand that became part of pop music history with its affordable and highly popular guitar amplifiers in the 1950s and 1960s. In this article, Honeycutt revisits his own journey with the brand and looks at some of the most famous Silvertone examples. Today, a Silvertone Twin Twelve like the one Honeycutt used in his high school rock band is a highly prized reference for many enthusiasts. And there's a lot to discover in the company's tube circuits, manufactured by different sources, including by Danelectro.
All great reasons to download your April issue ASAP. Please remember that all the content contained in every issue of audioXpress is the reason this publication continues to reinforce its role as an essential resource for the audio industry, month after month, 12 times per year. Your support and that of our advertisers is what allows us to keep this publication in print and on all the digital platforms as well as pay our independent authors and contributors for their work.
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