audioXpress Magazine      December 2023

  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.

Editorial: Ten Years More Of Everything
audioXpress is committed to serving the enthusiasts and global audio engineering
community.
Editorial By J. Martins
Even though my involvement with this publication started earlier, it was in November 2013 that audioXpress received a facelift, signaling a new life for this publication. We expanded the content and increased our focus on audio research and development (R&D), product design, and acoustic science while maintaining our roots in DIY audio and audio electronics. Over the years I have constantly re-examined those directions and more importantly worked tirelessly to expand our authors' network in line with the technology evolution and constantly evolving audio industry trends. As is always recommended on editorial projects, every year we have re-examined our mission and what was achieved, reflecting both our audience's interests and readership expansion across product and market segments.
---> Ten Years More Of Everything.

5 Supporting Companies

Features
22 Improving GaN With Digital Control
Axign Class-D Audio Amplifier PWM Controller
Demonstration Board
By Stuart Yaniger
The AX5689 is an eight-channel audio amplifier
controller IC with digital inputs and CMOS level PWM
outputs, enabling high-order digital control loops with
post-filter feedback. This article reviews the reference
design board using GaN Systems output devices,
configured as a two 500W channel BTL (2Ω) at 50V.

28 New Ways To Measure Noise Cancelling, Transparency,
And Other Modes In Headphones And Earphones
By Brent Butterworth
Now that headphones and earphones are adding
situational awareness, hearing protection, and
hearing enhancement features, it's time to come up
with new test methods to evaluate these functions.
HEAD acoustics has some ideas.

40 Optimizing Variable-Frequency Tone Controls
By Douglas Self
Douglas Self says bass and treble tone controls are
essential in a hi-fi system, and variable–frequency bass
and treble tone controls are desirable because of their
much greater flexibility. This article discusses optimizing
a variable high-frequency and low-frequency equalizer.

46 JFETs In The Variable-Resistance Mode
And Their Application In Audio Circuits
By Dimitri Danyuk
This article explores the variable-resistance mode of
JFET operation and describes a practical circuit, built
around JFETs in the variable-resistance mode with a
drain load resistor. The circuit is applied in a complete
phono preamp design in transconductance mode.

54 eDD — A Direct-Drive Amplifier For Electrostatic Speakers
By Jan Didden
Electrostatic speakers require drive signals
different from electromagnetic speakers. Where
electromagnetic speakers require up to 100V RMS
at up to 10A RMS drive levels, electrostatic speakers
require up to 5kV RMS, balanced, at up to 100mA
RMS. This project describes a well-performing
high-voltage amplifier to directly drive electrostatic
speakers.

Market Update — Residential Integration
8 Multiroom Audio: From Wired To Wireless
By J. Martins
Building on top of the whole-home infrastructure, multizone
and multiroom audio are exciting concepts in residential audio
integration. This article traces recent developments in that area.

Columns
Sound Control
36 Conference Room Acoustics
By Richard Honeycutt
Architects, interior designers, and facility owners now
have interesting options for conference rooms, including
materials to use in glass surfaces, that don't compromise
the acoustic performance.

Hollow-State Electronics
61 Tubes, BJTs, JFETs, MOSFETs, Or ICs?
By Richard Honeycutt
The history of semiconductor amplifiers, from the junction
field-effect transistor (JFET) to the Bell Labs transistor,
or Texas Instruments silicon-transistor, runs parallel to
the ascension and twilight of vacuum tubes. Likewise,
solid-state tube replacements remain a valid idea, gladly
offered by some manufacturers.

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