audioXpress Magazine      April 2021

  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.

Comment
4 This Issue's Editorial
From The Editor's Desk: Enhanced Audio Quality Frontiers
To design audio products, countless professionals are involved.
Editorial By J. Martins

5 Client Index

Features
48 Measuring Vibration with
Piezoelectric Sensors (Part 1)
The Research
By George Ntanavaras
Several years ago, George Ntanavaras designed a
system consisting of the ACH-01 accelerometer and an
amplifier with an integrated analog signal processor.
Over the years, he has been looking for other possible
solutions concerning the vibration measurements. In
this article, he describes his research for the design,
the construction of such a system, and presents the
results and the measurements.

56 The Science and Physics of High-
End Mic-Preamp Design (Part 3)
Considering the IC Options
By Mike Meechan
In the previous two articles, Mike Meechan discussed
the fundamental physics that play a part in
microphone preamplifier design, and briefly explored
its inhabitance in the practical world and how a good
design can retain the fidelity of the mic signal along
its path from transducer to output. At this stage,
he considers constructing some of the theoretically perfect
building blocks of an active mic preamp.

62 The Best of Two Worlds
An Old-Fashioned Tube Amp and Multilevel Class-D
Hybrid DIY Bass Guitar Amplifier Project
By Jens Tybo Jensen
This article describes the practical and basic
electrical design of a DC or battery-powered, 60W,
professionally featured and ultra-efficient bass
instrument amplifier. It is modelled after a classic
vacuum-tube bass amplifier topology, while utilizing
the exceptional audio quality and best in class
efficiency of the Infineon MERUS amplifier technology
to amplify every nuance of a genuine vacuum-tube
preamplifier.

Columns
Sound Control
38 One Traditional Way to Increase
Loudspeaker Directionality
By Richard Honeycutt

Audio Scope
44 Improving the Input Noise Model for a
High Output Current Dual Headphone Driver
By Michael Steffes

Market Update — True Wireless Earbuds
22 True Wireless Earbuds Evolving Toward Hearables
By J. Martins
There's a lot happening in the true wireless stereo (TWS) category
and this market update article intends to provide a quick overview
of the state-of the-art technologies and platforms in the space,
as well as some reference approaches in product design.

30 The Evolution of True Wireless Stereo
By Jean-Marc Luneau
In this article, we will look at some meaningful new features and
improvements that can help True Wireless Stereo (TWS) earbud
brands differentiate their products and make them stand out in today's crowded market.

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