For this first issue of 2025, audioXpress explores what stands out in terms of innovation in speaker technology. The first Market Update for 2025, titled “Performance Gains and Speaker Innovations” explores breakthrough designs as speaker drivers and transducers continue to evolve, sometimes incrementally, and sometimes delivering performance gains that were thought to be impossible. Find out which companies and products made it to the very short list.And focusing on Development & Design and still related with drivers and transducers, Mehul Kochar (Knowles Corp.) writes about the market for True Wireless Stereo (TWS) earbuds, which is witnessing a significant evolution with the rise of dual-driver or “hybrid” designs combining a dynamic driver with a balanced armature, a planar or a MEMS microspeakers handling different frequency ranges. This article explores how these different hybrid driver configurations enhance audio quality, user experience, and acoustic precision, offering a valuable option that allows OEMs to deliver superior features. The article also discusses the technological advancements that have enabled this shift, analyzing the advantages of different driver configurations.
Keeping the focus on Development & Design, Jacob Soendergaard and Frank Kettler (HEAD acoustics) detail methods to evaluate how listening effort and privacy can be affected by active sound design for electric vehicle sound enhancement systems. In “Enhancing In-Vehicle Communication,” the two authors showcase how to evaluate and assess in-car communication of spoken words from an occupant in a vehicle interior. They also evaluate the value of using headrest speakers versus door speakers for improved privacy of spoken word received through the audio system.
And moving on to Audio Electronics, Douglas Self shares his experiments with "Modern Op-Amp Distortion Tests." The renowned book author and audio circuit design expert 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 Douglas thought it was high time to evaluate those for distortion performance. In Part 1 of this article, he examines BJT-input devices. FET input op-amps are investigated in Part 2. Always using a similar protocol for five different loads and testing for basic op-amp distortion in favorable circumstances.
And, keeping with the practical aspects, this issue includes two completely different but extremely valuable reviews. To start, Philipp Paul Klose shares his experiments with the APL Virtuoso 2, a binaural renderer for multichannel and immersive audio formats. Based at the University of Huddersfield in the UK, Applied Psychoacoustics Laboratory (APL), founded in 2013 by renowned spatial audio and psychoacoustic engineering expert, Professor Hyunkook Lee, developed this binaural rendering plug-in and standalone application. Originally launched in May of 2023, APL Virtuoso is a culmination of more than 10 years of research into binaural audio and spatial sound, offering users the ability to mix and monitor immersive audio over headphones, without the need for complex loudspeaker setups. The ASPEN (APL Spatial Audio Engine) is the core technology developed by the research team. The v2 update of APL Virtuoso introduced acoustics emulation and externalization, simulating the experience of listening to loudspeakers in a perfectly tuned room.
Next-up, in one of his regularly contributed articles focused on Simulation Techniques, René Christensen writes about the intriguing topic of "Perturbation Methods in Audio Engineering." As he explains, standard simulations are closely tied to the analytical framework much more than the numerical. Simulation software gives insight into physical products that could not be achieved otherwise, often leading to less attention being paid to analytical methods and descriptive mathematical expressions related to the physical application. But these alternative methods can provide validation and simplifications to the simulation model that will solve faster, while approximating the same results. In this article, René explores an analytical approximation method described as a perturbation approach, before exploring other analytical approximation methods.
And we mentioned a second review, and this January 2025 issue of audioXpress includes the result of some intense experimentation by our own Jan Didden, in collaboration with Rens Tellers. The latest Purifi 1ET9040BA balanced Class-D amplifier module, a Bridge-tied-load (BTL) output stage, is the second product in the company's Eigentakt range. Following a conversation with members of Purifi during the 2024 Munich High End show, about the amplifier's audio performance being hard to measure even with the best available test equipment, Jan and Rens, took up the challenge, with invaluable support from Audio Precision's parent corporation Axiometrix. They also called the article "How to Challenge an APx555B" because that is the situation in which they found themselves, when specifications become extremely hard to measure, even with the best available test equipment.
And in this issue’s Hollow-State Electronics column, Richard Honeycutt takes us on a journey back in time to discover the roots of the modern-day, standardized phonograph equalization and learn about its impact on the very first hollow-state preamplifier designs. The schematics and comments presented in this article give us a clear idea of the circuitry employed and are a valuable insight for those interested in incorporating those hollow-state phono stages into today’s equipment.
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