audioXpress Magazine      October 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.

4 Innovation Happening Every Day
Today we enjoy advanced innovations that are easily recognized.
Editorial By J. Martins
On December 10, 1915, Danish engineer Peter L. Jensen and Edwin S. Pridham presented a groundbreaking invention to the public in Golden Gate Park in San Francisco, CA. It was the first practical application of a moving-coil loudspeaker, using a horn to amplify the sound. They successfully took their invention to market, building speakers for public address systems and for radios under the Magnavox brand. Much earlier, British physicist, inventor, and radio pioneer Oliver Joseph Lodge described the concept of the dynamic loudspeaker and was even granted a patent for a dynamic, moving-coil loudspeaker concept. Ten years after Jensen and Pridham successfully demonstrated a moving-coil loudspeaker, in 1925, Edward W. Kellogg and Chester W. Rice applied for the first of many loudspeaker-related patents. The "Sound reproducing apparatus" was issued in 1926, and the "Loud-Speaker" patent was issued in 1929.
---> Innovation Happening Every Day.

5 Supporting Companies

Features
8 Getting To Know Dutch & Dutch
By Jan Didden
audioXpress visited Dutch & Dutch, a company
founded in 2014 that managed to gain global
recognition with a single product — the 8c speaker. As
the company's founder Martijn Mensink explains, his
philosophy of designing a no-compromise speaker
that works together with the acoustics of the listening
room is paying off.

16 Measuring Loudspeaker SPL Response
And Harmonic Distortion At Low Frequencies
By Reinhold Lutz
This article discusses how to measure loudspeaker
SPL response and harmonic distortion at low
frequencies in a standard laboratory environment,
using a method that combines near-field
measurements with two identical microphones.

20 The AudioChiemgau ModeCompensator
A Quick Basic Test
By Rens Tellers and Jan Didden
The principles used in Dr. Reinhold Lutz's article
included in this issue are applied in a solution called
the ModeCompensator for precise measurement
of the sound pressure frequency response in the
presence of room modes, available from Lutz's
company, AudioChiemgau. Jan Didden and Rens
Tellers performed a basic functional test to find out
how well they could make it work.

42 Building A Minimally Baffled Dipole Loudspeaker
Part 2 — Measuring the Drivers and Developing the Crossover
By Charlie Laub
This article combines the theory, design, and
construction of an open baffle loudspeaker, including
crossover design, voicing equalization, and a practical
example built by the author. In the first part of the
article, the author reviewed the related theory and
the approach to practical design and construction of
the loudspeaker. In Part 2, he measures the drivers,
develops the crossover system, and describes his own
design.

50 Power Transformer Parameters, Selection, And Testing
Part 12 — Additional MFE Testing
By Chuck Hansen
This article concludes a comprehensive examination of
transformer cores, construction methods, materials,
testing methods, commercial power quality, and
design. We wrap up the series with an additional
batch of tests and some important considerations for
audio designers.

DIY Articles
28 Build The Popping Ps Filter
By Ethan Winer
Popping Ps are low-frequency impulses caused by air
blasts from a person speaking or singing into a
microphone. In this article, Ethan Winer shows an
analog circuit that removes these irritating sounds
from a live audio stream in real time.

34 The Bitches Brew Open Baffle Live Edge Speakers
By Perry Marshall
Highly praised at the 2022 Speaker Design Competition
sponsored by Parts Express, these large dipole speakers
named after the classic Miles Davis 1970 album have
stunning imaging and 120dB dynamic range.
The article from the author describes the full three-way
system construction made from book matched slabs of
spalted sycamore with a natural finish.

Columns
Sound Control
22 Passive Variable Acoustics
The Elusive Optimal Reverberation Time
By Richard Honeycutt
For decades, competent acousticians have been able
to design performance spaces optimized for specific
program material. Now it has become possible to tweak
the acoustics of a space for different program materials!
This technique is called "Variable Acoustics."

Hollow-State Electronics
60 The Western Electric 91E Amplifier
By Richard Honeycutt
In January 2022, Western Electric started taking
orders for its new 91E integrated amplifier. In this
article, we review the origins of this single-ended
amplifier and how it evolved to a totally new design
for the 21st century, offering over 20W per channel
— a first for the 300B.

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