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audioXpress Magazine April 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: Are We Going Too Far, Too Fast?
Knowing in advance that a particular approach is not feasible is also very valuable.
Editorial By J. Martins
As a premise for many articles that we review, support, and approve for audioXpress, there are many that actually suggest more questions than answers and essentially make us question our acquired knowledge. That's OK, and we encourage that. We should always look at new questions in order to find solutions for problems we ignored, disregarded, or simply were not aware existed. Please feel free to send us suggestions, abstracts, drafts, or fully expanded essays on audio-related topics. In any discipline. I fundamentally believe we have a long way to go to fully understand sound propagation and how to optimize our own electroacoustical systems to fully leverage sound reproduction. We continuously review research work and published material going back multiple decades — something we are forced to do to be able to recognize how much of what is being written today is actually new and "advances the evolution of audio technology" as our magazine motto states. And the more we do it with today's technology and acquired knowledge, the more we identify ignored problems, oversimplifications of concepts that were not understood at the time and were not considered to be relevant, and sometimes lines of thought that lead to a conclusion that was misleading because the author didn't previously eliminate potential variables in his own research. Does that make that work invalid or less useful?
---> Are We Going Too Far, Too Fast?

5 Supporting Companies

Features
34 Acoustical Engineering Via Various Expansion Techniques
By René Christensen
When dealing with design decisions in acoustics,
there are different ways to go. One is to make some
physical prototypes, take measurements, and try
to conclude from there which changes to make,
and continue in this fashion in an iterative manner,
hopefully landing on a satisfactory solution eventually.
For many problems, however, one can synthesize a
solution via a modeling setup, either analytically or
numerically. 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.

42 Built-In Guitar Effects
By Ethan Winer
Using a Fender Telecaster as an example, this simple
but valuable project demonstrates how to rewire a
guitar and add high-gain circuits such as a fuzz-tone
and a compressor. Ethan Winer's upcoming The Audio
Circuits Cookbook offers many great DIY ideas like the
one described here.

46 Low-Frequency Hybrid Crossover Filter
A Pseudo-Numerical And Switched Capacitor Filter
By Vincent Thiernesse
When Vincent Thiernesse needed a crossover filter
for his two-way system, he wanted a design allowing
him to change the crossover frequency with a single
control. The result is a unique and interesting design
mixing digital and analog techniques!

56 A Primer On Class-D Amplifiers
Part 1 — A Theoretical Review
By Paul Marchese
The successful design of high-performance Class-D
amplifiers requires a sound understanding of
the basic concepts, which this article addresses,
together with an actual build using a familiar Texas
Instruments IC as a reference.

Wireless Earbuds And Hearables
Market Update
8 AI, Sensors, And Next Steps In Personal Wireless
By J. Martins
The pace of innovation taking place in true wireless
earbuds and headphones is helping build the path to the
new and exciting category of hearables. This article summarizes
the latest examples of cutting-edge technologies and trends
in this space.

26 Innovative Wi-Fi Streaming For High-End Headphones
By Christoph Apel
As a leading developer in the audio streaming sector,
StreamUnlimited is continuously pushing the boundaries
to transform traditional audio systems into smart, connected
devices without sacrificing sound quality. Recognizing this
trend, StreamUnlimited developed an innovative Wi-Fi solution
tailored for both high-end and mainstream headphones,
redefining the wireless listening experience.

Columns
Sound Control
30 A Personal Journey Building Speaker Systems
By Richard Honeycutt
Discover how an article detailing a way to minimize speaker
cabinet-wall vibration helped spark a life-long interest in
designing and building custom speaker systems for
schools, auditoriums, and churches.

Hollow-State Electronics
62 Silvertone Instrument Amplifiers
By Richard Honeycutt
Learn more about Silvertone, a brand with an interesting
history in both consumer electronics and musical instruments,
which became popular in the 1950s and 1960s for
low-cost guitars and affordable guitar amplifiers,
all highly prized today.

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