I'm looking to learn about Air Motion Transformer technology

I'm curious about Wharfedale's use of Air Motion Transformers in their new Elysian line.  See http://www.wharfedale.co.uk/elysian4/

I'm admittedly in the dark about this technology even though other manufacturers have used it.  I'm curious about its use, potential benefits, sound signature, etc.
An air motion transformer is like an accordion. It has a pleated diaphragm that squeezes air out of the pleats when it vibrates so very little vibration will produce a lot of air motion. Just another way of matching impedance with air. They are easy to make as tweeters and will go down lower than most dome tweeters. Some of them run as low as 500 Hz. They will also go very loud. It is much harder to make a woofer with this technology but I think people are working on it. If you go to Parts Express you can see that there are many of them for sale and most are cheap. They have also been around since the 70's. My experience with them is very limited. The high end speaker industry has mostly avoided them for some reason preferring dome tweeters.  
AMT's are great designs IF you pay some attention to one thing. It is by far best for sound quality if the Diaphragm Former is made, as it usually is in any good design, from a silk material. The Former provides the physical support structure for the diaphragm material. It is meant to be as audibly transparent as possible and in fact has to be in order to do its job without resonating itself and adding its own coloration to the sound. The silk-derived Former is recognizable from its gray/whitish fibrous appearance, fairly semi-opaque or semi-translucent looking, although in some designs this might not be visible until the tweeter is disassembled. 

The problem is that some companies that make cheaper ATM's (often Chinese) use Kapton for the Former material. It's visibly a red colored plastic material and is pennies to produce. But, Kapton is not Nearly as audibly transparent as any silk-derived material and will noticeably color the sound, at least up to about 10kHz or so at which point it seems to no longer be resonating...but anything below that point is trouble.

Just avoid anything that advertises using Kapton and look for those ATM's that mention silk and you should be fine. This will bump up the price range your looking in, but it will be the difference between an ATM that lives up to its promise vs one that plainly doesn't.
In general, ribbon tweeters may sometimes have that last nth degree of uber detail or resolution compared to ATM's, but not by much at all. The difference may only make it a little easier to blend ATM's with the mid or woofer compared to ribbon. Ribbons tend to "beam" vertically more than ATM's - another thing that makes for easier driver integration for ATM's. 

Ribbons by design have the ribbon itself that is replaceable. It needs to be replaceable because it can get stretched if played too loud, at which point it can lose performance or even break. The cost of a new ribbon is much cheaper than the cost of a new tweeter.  ATM's don't have this problem, but they can take SPL's similar to ribbons without damage...but if you go Too far, you'll need to replace the whole tweeter - but, that's mostly only a problem if you're a metalhead or something :>)
FWIW, I took a peek at Wharfedale’s site and the Former shown in the exploded diagram of their AMT didn’t look familiar to me. It appears to be a yellow colored material and may possibly (I’m guessing here) be a more recent attempt to come up with a suitable Former material that performs better than Kapton, but is not quite as expensive to make as silk. Your guess is as good as mine on how good that one might sound.
In general, ribbon tweeters may sometimes have that last nth degree of uber detail or resolution compared to ATM's, but not by much at all. The difference may only make it a little easier to blend ATM's with the mid or woofer compared to ribbon. Ribbons tend to "beam" vertically more than ATM's - another thing that makes for easier driver integration for ATM's.

Ribbons by design have the ribbon itself that is replaceable. It needs to be replaceable because it can get stretched if played too loud, at which point it can lose performance or even break. The cost of a new ribbon is much cheaper than the cost of a new tweeter. ATM's don't have this problem, but they can take SPL's similar to ribbons without damage...but if you go Too far, you'll need to replace the whole tweeter - but, that's mostly only a problem if you're a metalhead or something :>)

I would imagine a Ribbon tweeter produces far more treble detail than any ATM. I usually don't hear any sound from ATMs other than a beeping when the buttons are pressed or the card is ejected. 
Dyslexia is known to strike at random, but it's rare that you see it so consistently when it does.
Ivan, thank you. You have really helped give me some knowledge to work with. I knew AMTs existed but have never confronted one. I like learning about what I don’t know.  
I own the Lawrence Audio Violin SE speakers which uses a front firing AMT tweeter and a rear firing ribbon tweeter for ambience.  I previously owned their earlier model which used a front firing ribbon tweeter only. The AMT tweeter is warmer and smoother sounding than the original ribbon tweeter. As stated above, ribbon tweeters, may have a higher range of detail but at times can sound fatiguing especially on poor recordings. I also experienced this with beryllium tweeters when I owned Focal speakers. Like all things, it comes down to equipment matching and your preferences. 
Hey there, I'm listening to some right now.

The potential is high, but not always realized. There are some damn awful sounding AMT speakers.

The one thing they all share is very low stored energy compared to dynamic tweets. However, their frequency response, and power handling can vary a great deal. The $2 Chinese units are not nearly as good as the top of the line European units. 
At the top end, AMT's are as good if not better than any other tweeter tech. At the low, they hurt.

Listen for yourself.
I also want to point something out.

The attention we pay to tweeters, and the amount we pay for tweeters, is really out of proportion with the amount of sound that comes out of them, especially in a 3-way speaker, only about 3 ish octaves.

There’s a lot more to a speaker than having a magic tweet, especially in terms of the total energy output.

Of course, being a geek about tech is what this forum is for. :)

Eric...you need to rethink that emphasis on those 3 octaves to also include the CRITICAL harmonics....see the imperfect amp thread..but ya, there are some AMT that are listenable, and antime the ATM is puking out cash, I am all ears...dyslexia or not...
also there is a decent wiki on AMT w links to the 8 patents...and ESS appears ro still manufacture the tweters in various sizes and complete speakers, might be a fun winter project...
A lot depends on the quality of the AMT ,in the Wharfe Dale 
maybe $50 each  top AMT can go over $400 each the bigger ones 
operate from the midrange to high frequency , I have had Dayton $70 AMT that were ok but lacked refinement, I have a Monitor audio Studio , which took a lot of technologies from its $25k flagship and its very refined and reasonably priced under $2k 
since I rebuild the Xover even in speakers over $14k many times it is the weak link using cheap Xover parts  just to save money .
80%  of speakers under $10k use what I consider at best average grade a Xover parts. Since it is the heart of your Loudspeakers 
everything goes through there are greatly determines the detail and refinement you get. I had the owner of Harbeth hang up on me 
when I questioned him on a $4k speakers using $3 Taiwan capacitors, being in the U.K. another $100 and using local Clarity capacitors would gain much more realism that is just one example 
even the $80k Martin logan using under $10 capacitors , I called them on it ,when spending good money like that you should get the top Of the line brand they choose to use. Makes no sense to me have some pride ,to me I would rather pay a little more for higher quality ,or just upgrade the Xover  .
Heil speakers used the AMT ribbon tweeters in their speakers back in the early seventies, if I’m remembering correctly. Those were the first AMT tweeters I’d ever heard of. They were ESS made I believe. You can still find them for sale on Ebay. They were German made (hence the Heil name of the inventor) so I seriously doubt they had any cheap Chinese plastics in them.


In full disclosure, we manufacture our own AMT drivers and AMT based loudspeakers here in the USA. We have lots of experience with ribbon technology as well.

As you may already know the ingenious AMT drivers were invented by the late Dr. Oskar Heil.

As with most things in audio there are many solutions to most design challenges. In many cases the implementation of a technology is more influential on sound quality than which technology is used. Yes, different driver designs have different characteristics but how they are used in the overall loudspeaker design is what's important.

The AMT design is fairly versatile but is almost exclusively used for tweeters. Generally speaking, I would say that a well engineered AMT can be just as detailed and resolving as the best ribbon drivers and would describe them as "lively" or "high energy". This is one of the reasons some speaker manufacturers find it difficult to integrate them into their loudspeaker design.

We designed our AMTs to be extended range drivers. In our Apollo line the AMT array covers from 120Hz to 24KHz. IMHO, AMTs can be excellent M/T drivers. As low mid-range and upper-bass drivers they are even more excellent but they have to be designed and built for the task.

IMHO, I wouldn't get caught up in what they are made from or whether the substrate is Mylar, Kapton or cardboard. Go experience a pair. Only you know if they are right for you. 



I just meant that relatively we overspend. Is a $2K tweeter with a $300 mid-woofer really a good balance?

P.S. - I am guilty of this myself. :)

So something like the Piega C711 is a real outlier.  Interesting technology, though.


"IMHO, I wouldn't get caught up in what they are made from or whether the substrate is Mylar, Kapton or cardboard. Go experience a pair. Only you know if they are right for you." 

Mike, FWIW, I had no intention of saying that 'only I know what's right' for @jbhiller and I don't think I'd ever want to say such a thing to anyone here. He asked a direct question and I gave him my best answer.

I'd like to think we mere mortals are allowed that sort of thing in a forum.

He's connected with Arion Audio, in Charlotte. 

I'm not trying to attack anybody at this point, I'm just hoping to get some clarification of what it was he meant to say, is all.


That comment wasn't aimed at anyone. Sorry if it offended you.

I was just trying to express the thought that a driver can't be judged by the materials it's made of. Sure, high end or exotic materials are cool and sometimes are required to achieve a design goal. Sometimes very common materials perform just as good or better than exotic materials. We use some very interesting adhesives and some very common ones. What's important is the use of the correct materials for the job.

All I am saying is it would be unfortunate for someone to avoid a good product because they don't understand this.

BTW, Kapton is often used in PRO AMTs because of its properties where durability is just as important as sound quality.

We don't use Kapton in our AMTs and our membranes are easily replaced if need be.


I'm far from the last word on AMT's and agree that little if anything should ever be prejudged in audio. OTOH, I just think it also is at least of some benefit to have as broad of a technical discussion as one is willing to entertain in a forum with its members. 

It was just that it appeared from what you posted earlier that you might have been implying that, despite the OP's clearly technical question, we should not consider any of these things and only concern ourselves with what we hear firsthand. (And if we were to apply that to the OP here, then why not anyone's technical inquiry, and so on)...it was a bit like we should dispense with the whole idea of discussion and just rely on firsthand listening only.

mijostyn1 ,

I'm with Arion Audio and Analysis Audio USA. We have been building AMT drivers since about 2009 mostly for custom apps. We are currently launching a loudspeaker line based around our AMT drivers.

I have a DIY pair of 2-ways and used the "Great" Heil AMT (the big AMTs, almost certainly from an old pair of ESS speakers) along with Altec 416s. After a couple of years I switched to the Beyma TPL150 AMTs. The Heils are bipoles with an open back, and sound a bit more airy than the Beymas. The Beymas are closed back and have a bit more meat, more bite on sax and horns and such. I prefer the Beymas but could easily live with the Heils which I keep for backup.

I think AMTs sound great, but of course I’ve heard many other tweeters that sound fantastic as well. The advantage for me is that the AMTs can go down to where the Altecs drop off (1K-ish), so a pretty good combination in a 2-way.
As many are aware, ELAC purchased Oscar Heils' AMT tweeter patent
in 1993, and took it much further with design upgrades that has resulted
IMO the finest tweeter on the planet. Their current jet 5 tweeter is killer.
During the past six months, while recovering from a massive heart attack,
I spent well over a hundred hours listening to HD videos on Youtube of 
the best high end speakers using my Koss Pro headphones on my HP computer with the Altec Lansing processor. I came to the conclusion
after listening to the ELAC FS series with the jet 5 tweeter, that it is the smoothest, richest tweeter I have ever heard during the past thirty years.
I test a tweeter with three musical instruments only, the violin, the piano, and the trumpet. Especially the violin where the jet 5 really shines resulting in the richest, smoothest and most natural tonal character I have ever heard to date through a tweeter and true music lover's of Classical and Jazz who own ELAC's with the AMT jet 5 know exactly what I'm talking about and would agree with my conclusion.
Most on here will most likely disagree with me about amt vs ribbon tweeters.  They do have separate patents, but that doesn't dismiss the FACT that they are different applications on a similar design.  
An AMT is a ribbon that has been folded.  This can change frequency, dispersion patterns etc,  but none the less dissect them both and you will find that a Air Motion Transformer is in fact a folded ribbon.
 Like a horn or dome or any design,  there are many variations and most sound different from one another.  To directly answer your question,  they are fast, typically fairly smooth, often, but not always have a rise on the top end.  Used properly,  AMT's are normally a very satisfying driver to listen to.  Like Ribbons,  you will find some excellent examples and some that can make your ears bleed.  So Not all are created equal,  good luck, Tim    
An AMT is not a ribbon.

In a ribbon the moving part is entirely conductive, and very low impedance so much that they usually require a matching transformer.

In an AMT the conductor is longer, much thinner and attached to a moving membrane which provides the actual moving surface area.  As a result the impedance is much more reasonable.

Further, AMT's have amazing power handling and linearity and lower distortion than most ribbons which tend to be delicate diva's by comparison.

Buy what you'd like!! :)


Post removed 
Any way you look at it, the transducer on amt is a ribbon that is folded. 
Yeah, if you ignore the shape, material, impedance. flow of current, source of opposing force and radiation pattern, I guess you are right, it’s a ribbon.

Ok the shape of material? AMT is folded. Impedance on  both are quite flat. Flow of current varies by the source of opposing force on both, we call these magnets. Radiation patterns are effected on both by mouth shape, horn load felting etc.  Don't let some cute answer fool you. Heil himself on occasion called his original AMT a ribbon dirivative. I own heil, and mundorf amts as well as fountek ribbons right now. 
Impedance on both are quite flat.

If you need to clutch at the shape of the impedance curve to call it a ribbon, while ignoring the impedance magnitude of the driver, and the transformer a true ribbon needs to be usable, and every other detail of the driver construction to be happy, please do.

Also, it’s "derivative", not "dirivative."
Arion, I just came from your web site and I really like a lot of what you are doing. Using the Trinnov for bass management duties is brilliant. I would never use an analog crossover in this position. Crossing at 120 Hz is also great. I cross at 125 Hz from ESL line source speakers to subs. IMHO people tend to cross too low were there are a lot of room problems which makes integration difficult. What I would like to see is Apollo 14's supplied with 4 sub woofers. The Apollo 12 is not quite tall enough to act as a line source down to 100 Hz where it still probably has significant output. So, as you move away from the speaker the mid bass will fall off. Two subs can only act as a point source so the low bass will also drop off as you move away from the speakers. You would need at least 4 sub woofers to create a linear array and balance the output.
With that efficiency rating you should be able to replicate a jet aircraft with 100 watts! I would love to hear them.

No, I don't need to clutch at the shape of an impedance curve. I clutch at the fact to make an amt, you take ribbon basic design and fold it. I've not argued differences. And once again you turn smart aleck. 
Semantics. IMHO, a ribbon and an AMT are very different. They may both be long and narrow so by some definitions they might be in the same category. They are both part of the light membrane transducer category as are planars and electrostats. Typically, in the audio world, the ribbon membrane is attached to its support structure only at the top and bottom. In AMTs the diaphragm is attached to its support structure at four sides. In this regard they are more like a planar. Some people call long narrow planar drivers ribbons. Some believe that a true ribbon driver uses only one metallic element as the membrane and the composite ribbons are not true ribbons. Others believe both are true ribbons. Features, construction and specs may be shared or be close but AMTs, planars and ribbons are all different.
Mike, Please excuse our old and outdated website. A new one with lots more info is in the works.

We use the Trinnov ST2 to control the AMT towers as well as the woofers. Our systems are designed with full DSP and room correction in mind. All filters and EQ is done by the DSP. The drivers are directly coupled to the amplifiers. The core is our AMT design and its ability to cover an extended range. Our 9 AMT driver Apollo tower can reach 80 Hz and below. Our 12 AMT driver Apollo tower just has more output. We have selected 120 Hz as the default crossover point for a variety of reasons. It can be easily changed through the DSP but we discourage it. Our woofers are designed to be stacked so room height is the limit. With their high sensitivity the Apollos can play to astonishing SPLs but no one should listen to those levels. Where their high SPLs count is with music peaks. Minimal dynamic compression.

Anytime you want to hear them just let us know.
And I would think Arion would know as he makes both types of speakers.
Having owned Apogee Divas I can relate to ribbons. His Analysis Audio speakers are strangely reminiscent of Apogee speakers. Mike, is there any connection to Apogee? I know, Apogee used a quasi ribbon woofer and it appears your speakers are using a design more like Magnepan. Ribbons are not just aluminum foil but aluminum foil traces laminated to a plastic. I think Apogee used very thin Kapton but I am not totally sure. The traces are connected in series which raises the impedance to somewhat reasonable levels. The impedance curve is extremely flat so in realty ribbons are a very easy load for an amp that can tolerate lower impedance's. Magnets run down both sides of the ribbon. A ribbon 6 feet long is very floppy so even though it is firmly connected at it's ends there are usually foam blocks placed at intervals to support the ribbon. You can not tension the ribbon too high or you will damage it. 
The Apogee bass ribbon was very easy to damage so I think the use of a planar magnetic design is smart. It is a much tougher driver. 
Thanx Mike I would love to. You wouldn't happen to have any dealers in New England?
Right now I use a TACT 2.2x for my front end which is more like The Trinnov Amethyst which is an ST2 with a few more inputs and a volume control. The room correction is identical. If my TACT were to fail that is what I would get at this moment in time.
I had a close relationship with Radomir Bozevic the DSP wizard behind  TACT. Do yourself a favor and do not sell anyone the microphone. Have your dealers set up the system, show the customer the basic stuff and remove the Mic. Boz got buried in phone calls. People were getting entirely lost in his program and coming up with inferior results which gave him a bad name aside from driving him crazy. His mistake was that he was direct purchase only and did not have any dealers to rescue the customer.
Anyway, stacking the woofers would be expensive. They would have to go all the way from the floor to the ceiling to create a line source that would go down to 20 Hz and match the output of the towers. You could take 4 subs and spread them across the front wall into the corners and achieve the same results. You have a horizontal line source! I do this with my ESLs with great results. No mater where you are the sound balance remains the same. Now my ESLs will not go as loud as your towers. Right now I use 4 12" subs. I would think 8 10" drivers would do the trick up to reasonable levels. To do  vertical line sources you would have to stack 6 or seven subs on each side? If you were to put them right into corners you might have output to match the towers which is academic really as nobody in their right mind would play it that loud.
There are no connections between Analysis and the now defunct Apogee brand. Analysis has been in business since about 1990. All Analysis M/T ribbons are designed with aluminum traces on a Kapton substrate. The main difference is the implementation. Most (all that I know of) ribbon membranes of the composite type are pleated through meaning the aluminum / Kapton composite are pleated together. Once done and suspended in the driver frame you basically have a spring. During assembly slight tension is applied mostly for symmetry. Over time they will sag. There are some negative consequences to that. Analysis ribbons are built differently. The Kapton substrate is not pleated. It is attached to the structure at the top and bottom with one to three cross-supports depending on which model and with slight tension. The pleated aluminum traces are applied to the substrate. Analysis ribbons never sag. There are several other benefits to the Analysis design. The Analysis bass panels are probably more like Magnepan panels but are, too, very different. They are also 3D in profile and have a complete suspension. Like most large ribbon or planar drivers they are an easy load on amps. Partially because of the design and the quality they are very stable and robust speakers unless you poke the membranes with sharp objects.
My car audio system uses AMT's ...I guess they're smaller to fit them all in the dashboard, kickpanels, etc.  There are good and not so good in all designs.  
Mike, Sorry that I missed your post. No dealers in New England but the VPI showroom in central NJ does have an Apollo System in house. Harry Weisfeld purchased an Apollo12 system for his home. His 12 will be at the VPI showroom for a few weeks before being delivered to his house. We are scheduled to deliver the Apollo system mid November. They have lots of very cool equipment there besides their turntables. It's worth a trip.

We do offer the Trinnov Amethyst as well. You make a good point about the mic and setup. At this point in time our systems do come with the mic to set up the system. The Trinnov does have remote setup capabilities. We are also available for on site assistance.

You are correct about the need for multiple woofers for SPL to match the Apollo towers but no one should be exposed to those levels. It's all about no dynamic compression. AMT based speakers can be great for HT too.

Don't know much about car audio but having good output for their size and being very clear, AMTs should work well in a car audio system.
The latest Elac  Jet 5 AMT Tweeter is made in Germany where the original AMT tweeter was developed not China like most,it is exception very fast ,detailed and very smooth using Neodymium magents all around 
and and folded pleated diaphragm . This works like a bellows,for the  folded tweeter they use a robot To solder the contacts to the mem brain .i believe theyuse a treated mylar membrain  it is very well thought out and complements their excellent mid-Bass crystal composite driver 
Aluminum  facet.sandwich with a pulp paper rear using 3 types of  adhesives  glue mid Bass driver  the Oder Elac I was not a big fan the new Vela seres Excellent .