Patent Review: Air Motion Transformer Passive Radiator for Loudspeaker

In the August 2018 issue of Voice Coil, James Croft combined the review of two important independent patents, having in common the fact that they try to address the shortcomings of the work of Dr. Oskar Heil with his Air Motion Transformer (AMT) woofer system. Following a review of a Tymphany patent, Croft reviewed a related patent for an Air Motion Transformer Passive Radiator, invented by and awarded to Eugene Julius Christensen (Aspen, CO).

In his report of the High End 2018 show in Munich, Ward Maas shares his findings in speaker design, amplification, turntables, and anything that showed innovations, an important improvement, better design, or simply because he couldn't resist it... Enjoy all his highlights while he walks the Munich Order Center (MOC) in this exciting edition, which was also complemented by a small but very enjoyable concurrent CanJam show in a nearby building.

In August 2018, as part of its Focus on Acoustics edition, audioXpress published an article documenting the cutting-edge research by leading acoustic experts, Jorge Castro, Nathaniel Bailey (Artnovion) Bruno Fazenda, Kelvin Griffiths (Sense Research, Electroacoustic Design) to determine improvements on precise low-frequency absorption, leading to Artnovion's latest Eiger Sub Trap range of acoustic panels.

For this test bench article, I characterized the DE780TN, a 1.4" exit titanium diaphragm pro sound compression driver from B&C Speakers. This compression driver is one of the latest additions to B&C Speakers’ extensive 17-model ferrite and neodymium motor 1.4" exit compression drivers. B&C Speakers supplied the ME90 horn for use with the DE780TN-8. This constant directivity horn has a 1.4" exit bolton type made from cast aluminum, and provides an 80° × 60° coverage pattern and a 900 Hz cut-off frequency. This article was originally published in Voice Coil, August 2018.

The TPL75 is one of the Air Motion Transformers (AMT, aka Air Velocity Transformer) that Acustica Beyma has developed for pro sound applications. Part of the success of Beyma’s AMTs for pro sound comes from its proprietary X-Bow technology, which opens as much as possible the mechanical constraint in the diaphragm, allowing it to manage higher temperatures, increasing the limit of the power the diaphragm can handle. This article was originally published in Voice Coil, August 2018.

For this test bench article, I characterized the New Eminence Alpha-5-8 5” line array/column array midbass driver. This a new 5” midwoofer from the American Standard Series, a 24-model transducer line of epoxy-acrylic finished stamped frame woofers and midranges. Applications for the Alpha 5-8 include use as a midrange in a multi-way speaker, as multiples in a line array, or as a compact column PA speaker. This article was originally published in Voice Coil, August 2018.

Noise distraction is the number one complaint for open plan office workers according to a recent study from Oxford Economics. Robert Manassero provides a fascinating account of how, after experiencing its own challenges with noise in an open office, Plantronics tested and developed its own solution to noise and distraction using biophilic acoustics or acoustics based on elements from nature. This article was originally published in audioXpress, August 2018.

A reinforced dose of everything that makes Voice Coil the Loudspeaker Industry must-read, the August 2018 edition features an updated directory on Voice Coil manufacturers, while James Croft reviews two patents directly inspired by the work of Dr. Oskar Heil on an Air Motion Transformer (AMT) woofer system. Finally, Vance Dickason characterizes three drivers in Test Bench, including the new Eminence Alpha-5-8 5” midbass driver; the TPL75, a compact pro sound AMT from Acustica Beyma; and a new pro sound compression driver from B&C Speakers.

In this edition, learn about Habitat Soundscaping and how biophilic acoustics can cure noise in an open office, get the latest on precise low-frequency absorption, and why you should be exploring acoustic modeling software and simulation apps. Richard Honeycutt writes about sound masking, Christopher Paul explains more on current feedback amplifiers, we report on the High End 2018 show in Munich and Neville Roberts heads to Venice, Italy, to report on a unique live recording experience!