ESS AMT-1 Air motion transformers ?!

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Has anybody heard or even made some speakers using the AMT-1 Tweeters. Or better midrange tweeters ?
I really need some info on them.


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diyAudio Moderator Emeritus
Joined 2001
Apparently, the company is back in business.


Rick Garret posted the following question concerning ESS:
Can you provide any information on Heil ESS louspeakers? I have a pair and would like to find any information I can on them. Thanks for your assistance. Rick Garrett


J.M. Willigens posted the following answer on the Heil ESS:
These loudspeakers used specific transducers, called "air motion transformers", which have nothing to do with ESLs. More with a ribbon transducer, in fact a folded ribbon was subject to a variable electromagnetic field, thus folding or unfolding and "quenching" air particles, which were forced to move in a vibration. The Heil ESS was an hybrid, as the air motion transformer was only good from medium upwards. The bass was an ED loudspeaker, quite often downward-firing. I am not sure, but think that Oskar Heil passed away, but some german company has reintroduced an ESS recently.


Barry Waldron posted the following answer on the Heil ESS:
In addition to J. M. Willigens' response, here is some background on the company. The company was founded in the late 1960s or early '70s in Sacramento, California. "ESS" stood for "E)lectro(S)tatic S)ound" and its first products were indeed hybrid electrostatic loudspeakers. There were various bookshelf and small floor standing models that utilized a Transmission Line woofer and single electrostatic tweeter.

One or more models used the B-139 6" x 9" oval woofer*. The tweeter was a single ended oval driver complimenting the shape of the woofer. As I recall, the speakers actually sounded quite good; moreover, the use of a Transmission Line was unique and an ideal match for the tweeter. This combination was not used again, commercially, until the introduction of the InnerSound EROS in 1997. (Audiophile hobbyists began using long Transmission Lines to compliment electrostats in 1977 after the publication of Roger Sanders' first homebuilt speaker project in "The Audio Amateur" magazine.)

As remarkable as these speakers were they did have two major limitations. The first was that the line length was necessarily short that prevented really low bass reproduction. (Subwoofers and bass commodes were not popular for several more years.) Second, the electrostat was limited for use as a tweeter by its single-ended design. (Modern ESLs are push-pull and incorporate a front and rear stator working together, along with a "constant charge" on the diaphragm, to reduce distortion and widen the driver's useful range. A single-ended speaker uses just a backplate ) over which rests a metalized Mylar diaphragm. Because the electrostatic force can only influence and control one side of the diaphragm and its resulting travel, distortion increases as it moves further away from the backplate. It is for this reason that the design is limited to tweeters and is no longer popular. (I find it interesting that some popular ribbon and planar magnetic speakers continue to be manufactured using the s/e design approach.)

My educated guess (not having interviewed company personnel) is that the company recognized these performance restrictions and was looking for ways to improve their products. Enter Dr. Oscar Heil and his amazing A)ir M)otion T)ransformer. This is a driver that uses a pleated diaphragm mounted vertically within a very strong magnetic field and motor structure. The action of the diaphragm is to "wiggle" the pleats and "squeeze" (to use the company's definition) out the sound at high velocity.

The company manufactured a variety of speaker beginning with the popular AMT-1. The AMT drivers were made in different sizes. To the best of my knowledge, ESS was the only licensee of the good doctor's creative genius. As Mr. Willigens noted in his comments, there is also a German licensee perhaps having obtained it through ESS.

During the heyday of the AirMotion Transformer, the most remarkable, yet outrageous development was the Transar (please correct me if I have the model name incorrect). This was a Rube Goldberg device that used a multiple of tiny soft plastic cones mounted vertically, one above the other. Several stacks were attached to the front of a baffle, each driven by carbon fiber rods that connected the many cones together. A voicecoil motor assembly was mounted at the bottom of the assembly. This speaker was a full-range AMT. It never achieved any degree of popularity. If you can find one, it should be preserved as a museum piece.

ESS moved its manufacturing facility several times and went dormant for a few years. The company is back in business and sells its products through company stores on the West Coast and some dealers on the Eastern Seaboard. It is my understanding that they have a sizeable export business.

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Last modified: Thursday, December 13, 2001

*The KEF B-139 is a woofer frequently used for transmission line systems. It is no longer made. It's sensitivity was 84 dB/1M/1W. I do not know if the fact that the B-139 was matched with the AMT unit means that the AMT had a similar low sensitivity. High frequency units are often, not always, more senstitive than the woofers with which they are matched. Kelticwizard.
diyAudio Moderator Emeritus
Joined 2001
According to the website, the AMT can crossover as low as 800 Hz.

Also, some more information here:
CTRL+F "heil"

I would just add that I auditioned some speakers using a Heil back in the seventies. To be honest, I was not at an age where subtlety was what I was looking for, and I mostly noticed that the speaker did not put out much basswise. It was not terribly expensive, though.

I do remember reading that the critics of the time thought the Heil unit was very good.
I worked in a Hi-Fi repair shop that was part of a large Chicago area Hi-Fi shop chain, Midwest Hi-Fi. This was at the height of ESS's early years. Not only did they build some great speakers but they built preamps and power amplifiers, as well as powered sub woofers.
If I remember correctly the Air motion Transformer had distortion almost as low as an electrostat did. The transformer was super efficient due to its huge magnet structure. All of the components as well as charging of the magnets was done in-house at ESS at the time. I recently tossed an old AMT-1 transformer out as the pleats were melted together....a common problem of these. I was also not aware that ESS was still around. Had I known I'd have more likely kept the thing. It made a great doorstop! I'm also pretty sure that Dr. Oscak Heil was the inventor of the Magnetron tube back in the ole days for radar.

We also did a number of experiments with the transformer and we found that a small rear baffle to delay the rear wave a bit made for a much better midrange. I also remember seeing the prototype full range "contraption" at the Consumer Electronics show in Chicago in the mid 70's. ESS was really a prolific company. I'm glad to see they're back.
Mark Gulbrandsen
Salt Lake City
From what I have found, you can change the ribbon for 120$ or something if you manage to destroy it. I seriously think about using these drivers but the price is very high. It has 510 Euro in Europe i guess thats a little less than 500$. Its quite a lot of money for drivers. But the good part is you need no midrange, it goes down to 1000-1200Hz at more than 96 dB. Very good for a 2 way speaker. the only thing you need is a mid-woofer arrangement that is also as good.
I don't think the 500.00 per driver is too bad. When you consider you'd have to either go with a ribbon or electrostat and either of these would cost even more to get comparable performance. One has to remember that the AMT is almost as good as an electrostat or ribbon transducer in the first place and capable of handling gobs of power. Melted diaphrams were common back in the 70's with these but back then really high quality power amplifiers didn't exist. I think Mark Levinson was just appearing at the time.
I now design and install sound systems for move theatres and I am going to be trying out an interesting new system from Stage Acompany which is a Dutch fim. They use ribbon drivers in their designs. The cabinets are only 9" deep, about 4 feet square, and with two 12" woofers and the ribbon unit capable of handling 1kw peaks without fatigue. They claim 130db spl max at that spec. Almost all of the Hollywood film mixdown studios have now gone to these speakers. They are also competitivey priced with JBL and E-V which are the other two popular brands of theatre loudspeakers. The SA ribbon unit is priced at about 700.00 or so.
Mark Gulbrandsen
Salt Lake City, UT
Hi, I have been using these pulled out from an old 1982 ESS speaker. They work fine, see my project I am still playing with:
The Heils are very good, perhaps better than all dome tweeters, better than Scanspeak 9900 I used. Because they have such a large radiating area the treble is extremely lush, detailed and full, like listening to several dome tweeters at once. They are very easy to work with & no peaks etc (audible).
However, I compared them with a Raven R1 recently and sadly the R1 is better, more modern sounding, extended & transparent, hard to believe really.
The Heil is still very good, some people have thought of using it as a cheap Raven R3. For midrange it is really only best above 2000hz or more. I have tried it in 3 way & 2 way & prefer the 5000hz xo point.
My email is if you have other questions.
Heil History

The original Heil Air Motion Transformer was really quite spectacular. I was lucky enough to have a pair in the mid 70's and at the same time a pristine pair of KLH-9 electrostatics. The two made an interesting contrast: The AMT was more dynamic, but the KLH had a slight edge on transparency and sweetness. Given the price difference between the two; the AMT was even more impressive.

To the best of my knowledge ESS has never dissapeared.... they've just been a bit obscure.

Oscar Heil is indeed deceased but before his death sold his older design to Eton, and started a new speaker called the Oskar Aulos.

Just as by-lines the great Nelson Pass and his wife were part of the original ESS and I believe largely responsible for voicing some of their better product. Dr. Heil was a prolific designer, responsible for the FET and some dramatic changes in geological exploration hardware.

Ahhhhh, The good ole days.
I wonder if Nelson was the designer of the ESS electronics? They had a couple of power amps, a preamp, and powered subwoofer. I can remember repairing the 200 WPC amps quite frequently back in "74". The bias adjust on it was a bit temperamental at best. At 12:00 it was properly biased but at 12:01 it blew the outputs and went up in smoke. When properly set up it was the best sounding amp in ts class. Quasi output of course with minimal U shaped heatsink(fins).
Mark Gulbrandsen
Just me again.....Check out these E-Bay Auctions of older ESS items. Kind of interesting.

Also here is a blurb about Oskar Heil. I forgot that he was a sort of Henry Kloss look alike.

Note that in the top Auction he claims they sell the Monitor for only 640.00 each! The AMT 1 Speaker sold for more than that in 1973! Seems really reasonable to me if that price is correct.
Mark Gulbrandsen
If you don't mind taking info from a new guy. But there is an ad for the ESS AMT speakers at or go to the Directory ( bottom of DiyAudio page ) under Reference click on Links and then the first link, Audio Links -The Biggest (?) list of Audio Links?. It will take you to And there is an ad window for PIEGA of Switzerland. There is pictures of completed speaker with the tweeter you are interested in.
Look at the Raven R2 as well. I think it is about US$300, again cheaper than the Heil.

You really should get Heil out of your head, they are good but there are modern tweeters such as the Ravens that are better. The R2 has 2 times the radiating area as the R1 and should be more dynamic and better.

All Ravens can be used to crossover at around 2000Hz but higher is probably better. I will be exchanging my Heils for Ravens soon.

Trust me! :)
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