audioXpress September 2020 Speaker Focus Edition Is Now Available!

Our always popular loudspeaker edition is now available online and in print! audioXpress'  Speaker Builder, Speaker Focus edition covers loudspeaker building, design, and testing with a balanced amount of DIY, speaker history, theory, R&D, and manufacturing articles. Read two articles about speaker history, a review of the Magnepan LRS, explore the details of two amazing speaker builds, and learn how to do loudspeaker measurements at home. And there's much more in speaker research and development, measurement, and production!

For our readers who always enjoy a bit of history, this issue will be a pleaser. Scott Dorsey revisits his favorite movie theater speakers, the Altec Lansing's Voice of the Theatre Series. Dorsey knows cinema sound inside and out, and in this article he shares his personal thoughts about these highly valued horn designs, and provides valuable tips on how to restore them.

Also revisiting a bit of history, in his Sound Control column Richard Honeycutt writes about "The Roots of Early Live-Sound Speakers." From the origins of live performance in ancient Greece to Peter Jensen, and Edward Kellogg and Chester Rice, and from Western Electric to Klipsch and JBL, this article reminds us of how far we've come in electroacoustic sound reinforcement.

In his Audio Scope column, Michael Steffes ponders: "How Do We Generate Measured Noise Plots for Op-Amps?" After all, every amplifier introduction includes some effort at an input referred noise plot from measured data on a "typical" unit. Only output noise can be measured, so how are these input-referred plots generated? In this article, Steffes details the measurement set up.

And we couldn't have an edition of audioXpress without a review. Forced to shelter at home, Oliver Masciarotte looked around his home base in the Twin Cities, and decided it was time to have a serious look at the Magnepan LRS (Little Ribbon Speaker) the company's latest affordable, full-range quasi-ribbon speaker. Yes, Magnepan is the famous company that's been manufacturing the Magneplanar loudspeakers since the 1970s. The latest two–way Magnepan LRSs are much smaller, a mere 1-inch thin, and definitely worth examining. For this review, Masciarotte writes about what he heard, while Kent Peterson measures its performance in the lab.

And in the best tradition of Speaker Builder, this edition includes a double dose of speaker DIY. Starting with George Ntanavaras, detailing his fascinating APR-17 Aperiodic Loudspeaker project. Having previously explained the concept of an aperiodic loading loudspeaker and exploring the design, in the second part he shares the crossover design and discusses the measurements he took to evaluate the result. He also describes a passive equalizer that he used to boost the loudspeaker’s low-frequency response.

And, Chris Biese shares his design for the RSX speakers, which won first place in the Dayton Audio category at the 2019 Midwest Audiofest hosted by Parts Express. This "Large, Modern DIY Speaker" will surprise anyone who understands speaker building, both in the audacity of the driver combination, which includes making a DIY coaxial speaker (twice, of course), the dipole design, expanding the lower frequencies with a powerful subwoofer enclosure with two large passive radiators on each side, and the three-way crossover design. 

And we asked our friend Geoff Hill, the inventor of the original tetrahedral test chamber (TTC), to explore how to do loudspeaker measurements at home. For those of us without an anechoic chamber at home, Hill explains how to build our own test chamber. With the build description, he also provides a valuable guide on alternative loudspeaker measurement techniques.

Next up, Stefan Irrgang and Wolfgang Klippel (Klippel GmbH) contributed an article that addresses important loudspeaker measurement questions, this time for quality control and end-of-line (EoL) testing - enabling users to "reliably separate faulty from fault-free devices under test (DUT) and to minimize false positive or false negative verdicts." Specifically, the two experts focus on testing irregular defects (also known as Rub & Buzz), which in most cases can only be detected by acoustic measurement.

And many unfortunate product design problems in loudspeakers could actually be avoided with a more extensive research process, building and measuring hundreds or thousands of prototypes... correct? Knowing that's an impossible approach in the real world, Dr. Alfred Svobodnik and Thomas Gmeiner, respectively CEO and President, and Director of Engineering of the Mvoid Group, contributed an article on how modern methods of acoustical virtual product development make it possible to assess and optimize quality and performance problems throughout the entire product development process. Using a combination of modeling, simulation, and measurement tools, everything can be analyzed in-depth before building any physical product, the two experts explain.

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