audioXpress Magazine      January 2025

  audioXpress remains the authority on audio and reproduced sound by connecting manufacturers and distributors with developers, buyers and consultants around the globe! It's readers are the audio product designers, consultants, integrators, DIY enthusiasts, opinion leaders and your best customers. All of them agree that the coverage of trending topics, unique in the audio industry, make audioXpress a must read.

Every month, audioXpress combines the best educational articles on topic such audio electronics, speaker and headphone design, amplifiers (from tube to Class D), acoustics, practical test and measurement, audio engineering praxis, and standards. audioXpress provides inside stories on new audio developments, on R&D Stories, the most complete objective reviews of innovative products and software, and selects some of the best DIY audio projects from worldwide experts.

From the Editor's Desk: New Speaker Priorities
How many new loudspeakers are now being designed.
Editorial By J. Martins
Many brilliant speaker engineers I know, particularly those more actively involved in the industry, have in common a shared understanding of the limitations and strong compromises needed to create products that actually reach consumers. They are fully aware that the speaker is the weakest link in the sound chain and that its efficiency is lower than anything they dare to discuss. Paradoxically, they all share a profound belief in their mission to achieve performance gains according to the intended application of their work – with listening performance being the ultimate goal, albeit with the inevitable compromises. But performance can be an elusive metric, depending on the intended application goals of the finished product. A speaker driver is just a component in a loudspeaker system design, as Vance Dickason reminded us in his recently (re)published text about the purpose of his Test Bench characterizations. "Whether a particular driver ends up sounding good or bad to a large extent depends on the application and the skill set of the systems engineer designing the product.
---> New Speaker Priorities.

5 Supporting Companies

Features
34 Modern Op-Amp Distortion Tests Part 1
BJT Input Devices
By Douglas Self
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 Douglas
thought it was 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.

44 APL Virtuoso v2 Binaural Renderer
For Multichannel And Immersive Audio Formats
By Philipp Paul Klose
Applied Psychoacoustics Laboratory (APL) developed
Virtuoso v2, a binaural rendering plug-in and
standalone application. Originally launched in
May of 2023 and now updated with significant
enhancements, 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.

50 Perturbation Methods In Audio Engineering
By René Christensen
Standard simulations are much more closely tied to
the analytical framework than the numerical. This
article explores an analytical approximation method
described as a perturbation approach.

54 Purifi 1ET9040BA Balanced Class-D Amplifier Module
By Jan Didden and Rens Tellers
This article follows a conversation with members of
Purifi Audio during the 2024 Munich High End show,
about the audio performance of the 1ET9040BA
balanced amplifier module being hard to appraise
even with the best available test equipment. With
support from Audio Precision, audioXpress took up
the challenge.

Drivers And Transducers
8 Market Update: Performance Gains and Speaker Innovations
By J. Martins
Speaker drivers and transducers continue to evolve,
sometimes incrementally, occasionally delivering performance
gains that were thought to be impossible. In this article we
explore breakthrough designs and new loudspeaker challenges.

18 The Rise Of Hybrid True Wireless Stereo Earbuds
Exploring Dual-Driver Innovations
By Mehul Kochar
The market for TWS earbuds is witnessing a significant evolution
with the rise of hybrid designs featuring various types of drivers.
This article explores how different hybrid driver configurations
enhance audio quality, user experience, and acoustic precision.

26 Enhancing In-Vehicle Communication
Analyzing Listening Effort And Acoustic Privacy
By Jacob Soendergaard and Frank Kettler
This article details methods to evaluate how listening effort
and privacy can be affected by Active Sound Design for
Electric Vehicle Sound Enhancement systems. Results on
in-car communication of spoken word from an occupant in a
vehicle interior are complemented with suggestions for enhancing
the communication experience.

Columns
Hollow-State Electronics
60 The Path To Standardized Phonograph Equalization
By Richard Honeycutt
Discover the roots of modern-day equalization and learn
more about the hollow-state phono preamps in today's
equipment. Not many manufacturers allow publication of their
schematics, however the ones shown here give an idea of the
circuitry employed.

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