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Positive Feedback ISSUE 71
january/february 2014


by Victor Chavira


The story of ESS is curious. Founded in 1972 and based in Sacramento, ESS produced speakers that featured an innovative mid-tweeter called Air Motion Transformer designed by Dr. Oscar Heil. The Air Motion Transformer was notable in that the very thin pleated membrane does not directly engage the air to produce a pulse as with all dynamic drivers. Rather, the AMT membrane squeezes together like an accordion that creates minuscule variations to the air in front of and behind the pleated membrane resulting in an amazingly transparent sound wave. The technology is very robust and can accommodate a crossover point as low as 800 Hertz. ESS is an acronym for electro static sound. However, ATM mid-tweeter does not require being plugged into an AC wall socket to charge its membrane like all electrostatic speakers.

Throughout the 1970s to the early 1990s, ESS experienced varying degrees of success. By that time, ESS had come under the ownership of a then popular home electronics chain called Leo's Stereo in Southern California. Challenging economic conditions in 1991 led to the consolidation of home electronic stores and shuttered many smaller audio specialty shops leading Leo's Stereo to eventually file for bankruptcy. Without an established outlet for its products, the ESS production facility in Sacramento closed its doors.

Meanwhile, the ESS AMT1 had amassed a loyal customer base throughout the world. Music lovers and audio nerds nostalgically recalled ESS in the same reverential manner as companies like McIntosh and Quad. Subsequently, the patents for pleated membrane technology have expired and other companies have been developing and applying the design in their products. Although, ESS still retains the rights to the Air Motion Transformer trademark.

One sunny Southern California day, I had the opportunity to visit the renaissance of ESS at a plant that previously produced subwoofers in South El Monte, about twelve miles east of Los Angeles. There I met a man named Rick Caudillo. Mr. Caudillo has been entrusted with the task of rebooting ESS. This task required relocating all of the ESS R&D, parts, and tooling from as far away places as Germany. Here in this nondescript shop, Mr. Caudillo and a small team of craftsmen painstakingly recondition and upgrade ESS speakers from all over the world in addition to making authentic and made to order AMT1 models. After spending some time around the shop, I loaded a pair of AMT Limited Edition speakers into my car and headed home for a listen.

Installing a pair of ESS speakers is no easy task. The cabinets are robustly built and weigh about 45 pounds each. Great care must be taken not to handle to AMT by the mid/tweeter module that protrudes from the top of the stocky woofer box. Fortunately my older son was available to help me ease the speakers from the car and set them down on the living/listening room floor. Despite their stout appearance, the AMT is a large speaker and can radiate massive amounts of sound in both directions with its bi-directional AMT module and 12 inch dynamic driver with rear mounded passive radiator. After some experimentation, the speakers were positioned about one third of the length of my 13 by 20 foot room.

One of the first selections I listened to was Man of Steel movie soundtrack by Hans Zimmer. Several of the tracks feature 10 of the world's top studio drummers playing full kits simultaneously in a 2 by 3 rectangle of percussive power. The AMT delivered huge, dynamic, and uncompressed sound that immersed the listener in a sensational experience. Other tracks focus on the sound of musical steel sculptures stroked with brushes or struck my soft mallets. The AMT revealing nature left no doubt in the listener's mind about the cool clang of steel and shimmery overtones brass. The overall sound of the AMT LE offered the ribbon like speed and transparency in the mid range frequencies and beyond skillfully blended with force and low end extension of modern dynamic systems.

The rear of the bass cabinet contains a high frequency adjuster called a brilliance control by ESS. The linear potentiometer attenuates high frequency prominence to suit the listener's needs. Therefore, the AMT LE can go from bright to mellow with a turn of the dial. Again, after some experimentation, I set the knob in the range between seven and eight o'clock for the duration of my home audition.

Solo piano works were superbly rendered with the AMT LE. Chopin's Etude No. 3 in E Major, Op. 10 as played by Idil Biret on Naxos sounded convincingly lifelike and present in the room. The soundstage was immersive and ultra transparent reminiscent of much larger and more expensive speaker systems.

If you followed my articles over the years, readers know than I like to recommend a Latin Jazz selection for your enjoyment. Two songs should make their way into your playlist this time. The first is Solid by trombonist Wayne Wallace form his album Bien, Bien! The electric bass lays down a fat and funky tumbao that propels and motivates with energy. Percussive attacks flashed with instantaneous speed and precision. Trombone sang agile grace and vigor. The second song is "Cachita by Candido & Graciela" from their 2004 Chesky recording Inolvidable. The recording was done live in studio with great regard for real space and decay of sound. The primary melodic instrument in this song is flute with accompaniment from piano, violin, tres, bass, and percussion. The ATM projects a panoramic of the proceedings and resolve fine details deep in the sound field.

I brought the ESS AMT Limited Editions home with the intent of not returning them for a very long time if at all. Alas, after about three weeks, I packed up the classics and returned them to the shop. As entertaining and satisfying as the AMT are, they were ultimately too much speaker for my situation. If I had a larger acoustically treated and dedicated listening room, the AMTs would be near the top of my list of speakers to audition under $5000. The AMTs are probably the most revealing speaker I've ever had the pleasure of listening to in my home environment. Fortissimo orchestral climaxes and movie special effects played back and very loud levels sounded effortless for the AMT. It's no wonder that in their heyday, AMT1s were considered essential tools for recording studios to evaluate their work.

If you value the great sounds of classic audio or are just curious about the amazing Air Motion Transformer module, give ESS a call to arrange and audition. Mr. Caudillo and his team are eager to build you a pair made to order.