audioXpress Magazine March 2025

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audioXpress Magazine March 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: How Things Measure
Pretending to represent defendants of science and public interest.
Editorial By J. Martins
As I was walking at an accelerated pace along the Las Vegas Strip for another CES 2025 meeting, while passing in front of Harrah's, the sound of a street musician playing saxophone over a pre-recorded music track inevitably captured my attention. The music was loud enough to mix perfectly with the acoustic sound of the instrument and provided a pleasant background for all those passing by on that cold January morning. As I glanced at his setup, a fairly large battery powered speaker stood out on the floor, still with large, colorful retail stickers proclaiming "2500 Watts!" I couldn't help smiling as I tried to understand the unknown brand logo for the clunky apparatus. Well, the brand doesn't really matter, because there's no lack of 2500W active speakers advertised online, as a quick search will reveal. Likewise, there's no lack of compact, portable Bluetooth speakers advertising 180W. You will need to reach for detailed specifications to learn that this is the "total amplification" resulting from 2x 40W woofers plus 4x 25W for full-range speakers.
---> How Things Measure.

5 Supporting Companies

Features
8 Audio THD With QSPICE
An Interview with Mike Engelhardt
By Tim McCune
Simulation is used in all areas of audio design, but
specific guidance on how to best use it for audio is
scarce. We asked Tim McCune, former president of
Linear Integrated Systems (Linear Systems) currently
consulting for Qorvo, to interview Mike Engelhardt,
the creator of the QSPICE simulation suite and discuss
how this increasingly popular tool can help solve
many issues that audio designers simulating their
circuits might confront.

14 The Analog Engineer Calculator And
The Analog Engineer's Pocket Reference
By Jan Didden
Do you know that Texas Instruments offers a
PC-based calculator designed to speed up and support
circuit design efforts? This calculator pairs well
with the concepts described in the valuable Analog
Engineer's Pocket Reference, which we will explore
here.

38 The SL-100 Sound Level Adjuster
By George Ntanavaras
Here is a very useful piece of test equipment that
is easy to build, and its cost is low. It is particularly
helpful, especially if you must calibrate a loudspeaker
measurement system very often.

46 Reinforced Speaker Protection
By Thomas Perazella
This article describes an upgraded speaker protection
design for a multichannel home audio system, using
back-to-back power MOSFETs in place of relays to
make or break the speaker connections. The system
also includes reinforced protections for the updated
and very powerful amplification rack.

56 Zoran M. Dukic's High End Tube
Amplifiers Designer Tool Box
By Jan Didden
This book really is a tool box — a one-stop resource for
everything you need to design and build a tube-based
audio power amplifier. This self-published book has
the same content quality as a book from the larger
publishing houses.

60 A New Op-Amp For Phono Preamps
Part 2 — Development And Measurements
By Brian Lowe
In Part 1 of this article, Brian Lowe developed the
concept of the discrete op-amp and explored some
design options and devices. In Part 2 he further
develops the discrete op-amp design by adding
Folded Cascode and Transimpedance stages and an
output buffer. Part 2 concludes with simulations and
measurements.

Test & Measurement
20 Measuring HDMI Audio
By Steve Temme
From its origins in 2002 as a new, smaller connector
for HDTV, High-Definition Multimedia Interface (HDMI)
evolved over the years to become one of the most widely
adopted interfaces. This article provides practical answers
on how to perform HDMI audio measurements, dealing
with the interface's multiple options and configurations.

26 Testing Power Amplifiers
By Adam Liberman
Power amplifier testing requires consideration of current,
voltage, thermal characteristics, and load properties.
This article covers the fundamental measurements for
testing power amplifiers, with specifics on how to best
accomplish the tests using Audio Precision's APx series
audio analyzers and APx500 measurement software.

Columns
Sound Control
32 The Early Days of Speaker Acoustics
By Richard Honeycutt
Experiments from early speaker designs, such as
building cabinet walls that helped to damp panel
resonances and its effects, remain valid guidelines.
This is a personal perspective of that evolution and
lessons learned.