Are you ready to try an Air Motion Transformer Tweeter?

[Jeff B.]

I commented in my CEDIA report that the new fad is use the new Air Motion Transformer tweeters that are out there or "Air Striction" as they are sometimes called.

These tweeters were used extensively by ESS back in the 80's and were invented by Oscar Heil a few years before that. The larger ones are massive is weight and are generally dipoles. However, the smaller ones were about the size of a normal tweeter and were configured as monopoles. The new ones are very similar to this latter design. Eton has had one for sale for many years, but they are very costly. Now, we are able to get one that isn't any more money than most other good tweeters. After listening to them at CEDIA I have decided to build something using this tweeter and try it out. I liked what I heard and thought I would see just what it could do.

I am working with the Airborne RT-4001
It is available here:

http://meniscusaudio.com/airborne-rt4001-p-1201.html

Here's a pic of mine:


So, here's what I am going to do for those of you who may be interested in this idea too:

I measured the response of the tweeter and its distortion, and Mark K. did a great job of measuring its off-axis response, which is really very good. I will post all of that here.

So, what is the tweeter like? It has a heavy cast face-plate with slotted openings. Inside you see the accordian style Kapton diaphram. Think of the tweeter as a planar device that has been folded up. It has a very large radiating area in a tweeter not much larger than a 1" dome tweeter. As the voltage passes through the tweeter its pleats move in and out, thus "squeezing" the air out of the folds.

Here is vertical response family:


Here is the horizonal response family:


You will note that the tweeter is very well behaved off-axis to 30 degrees in both directions. This is exemplary dispersion.

The impedance is like that of a 3 Ohm resistor.


And finally here's the distortion plots I took this afternoon (ignore the data below 1khz):


All distortion, but especially nasty odd-order distortion remains remarkably low. It looks like an excellent tweeter to me.

And now, if you want to experiment a little I have attached the frd and zma files below. You just need to download them and change the extension from to .txt to the appropriate .frd and .zma, import them into your favorite crossover designer and go from there.

Isn't this hobby great?:D

Jeff B.

[framus]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I commented in my CEDIA report that the new fad is use the new Air Motion Transformer tweeters that are out there or "Air Striction" as they are sometimes called.

These tweeters were used extensively by ESS back in the 80's and were invented by Oscar Heil a few years before that. The larger ones are massive is weight and are generally dipoles. However, the smaller ones were about the size of a normal tweeter and were configured as monopoles. The new ones are very similar to this latter design. Eton has had one for sale for many years, but they are very costly. Now, we are able to get one that isn't any more money than most other good tweeters. After listening to them at CEDIA I have decided to build something using this tweeter and try it out. I liked what I heard and thought I would see just what it could do.

I am working with the Airborne RT-4001
It is available here:

Here's a pic of mine:


So, here's what I am going to do for those of you who may be interested in this idea too:

I measured the response of the tweeter and its distortion, and Mark K. did a great job of measuring its off-axis response, which is really very good. I will post all of that here.

So, what is the tweeter like? It has a heavy cast face-plate with slotted openings. Inside you see the accordian style Kapton diaphram. Think of the tweeter as a planar device that has been folded up. It has a very large radiating area in a tweeter not much larger than a 1" dome tweeter. As the voltage passes through the tweeter its pleats move in and out, thus "squeezing" the air out of the folds.

Here is vertical response family:


Here is the horizonal response family:


You will note that the tweeter is very well behaved off-axis to 30 degrees in both directions. This is exemplary dispersion.

The impedance is like that of a 3 Ohm resistor.


And finally here's the distortion plots I took this afternoon (ignore the data below 1khz):


All distortion, but especially nasty odd-order distortion remains remarkably low. It looks like an excellent tweeter to me.

And now, if you want to experiment a little I have attached the frd and zma files below. You just need to download them and change the extension from to .txt to the appropriate .frd and .zma, import them into your favorite crossover designer and go from there.

Isn't this hobby great?:D

Jeff B.

I've been working with this tweeter as well, and I've been a little less impressed. The 10 dB demarcations you show are a little flattering, and mine measured with a pretty humongous peak at 15 kHz on a typically sized 2-way baffle (see attached). Still, it's the best mini AMT I've used, and it's capable of good perfomance with some careful crossover work.

[[email protected]]

Re: Are you ready to try an Air Motion Transformer Tweeter?

are you thinking 3-way?

[neildavis]

Re: Are you ready to try an Air Motion Transformer Tweeter?

Isn't this hobby great?:D

Jeff B.

I bought some of the "raw" diaphragms that aren't even folded yet (hey--this is DIY, right? :D). I'll post some pictures tomorrow. It's good to see some favorable distortion measurements.

The diaphragms I got are for the RT2000 and the RT5000. The RT2000 diaphragms were on the order of $3 each. However, it cost me $35 to do a bank transfer to China, plus they charged my Fedex account a whopping $85 for shipping a very small box :eek:

Things are busy at work right now, but I'll be free at the end of the year. Four of the RT2000 diaphragms should fit nicely into the magnet structure on the left in picture below.

[Wolf]

Re: Are you ready to try an Air Motion Transformer Tweeter?

are you thinking 3-way?

Nope- you can use these to 2kHz, Lowell. $78 though.

I'm interested in the next model down, as it's good to 3kHz and is only ~$45.

Later,
Wolf

[Paul Carmody]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I've been working with a pair, too. I threw together a 2-way using it and a Seas Excel 5.5", crossed around 2 KHz. I really enjoyed the sound of the tweeter (woofer too ;))

I had a really cool idea for a 2-way with this tweeter, but the midwoofer I wanted to use is caught up in the current Neodymium crisis... so that project is on-hold.

[Jeff B.]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I've been working with this tweeter as well, and I've been a little less impressed. The 10 dB demarcations you show are a little flattering, and mine measured with a pretty humongous peak at 15 kHz on a typically sized 2-way baffle (see attached). Still, it's the best mini AMT I've used, and it's capable of good perfomance with some careful crossover work.

Hmmmm..... Well, I attached my frd file, and those are my actual measurements at 2.83V at 1 M on the tweeter axis *except for the added low frequency extending). I did not get that peak at 15 kHz. I have another sample that should be arriving today, I will have to see if it measures the same. Below the peak your measurement is pretty flat and matches mine fairly well.

[greywarden]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I'm really digging these new FRD-file posts, I wish my computer hadn't hiccuped now more than ever! I lost all of the designs I did, too! So I'll definitely have some time when I get settled in at home.

[JimHRB]

Re: Are you ready to try an Air Motion Transformer Tweeter?

Interesting. I heard the original ESS AMT3 "Rock Monitors" back in the 1970s and was very impressed. They were 3-way towers with the dipole AMT on top. I still have the brochure in my file cabinet.

[DoubleTap]

Re: Are you ready to try an Air Motion Transformer Tweeter?

Somebody I know put together a design using that Airborne AMT and said they love it ... since then I've had it on my radar as something to try.

Right now I'm just about finished with a design that has the Beyma TPL-150/H on front with a AE TD10M, and the Aurum Cantus AST2560 as an ambience tweeter. Both the Beyma and AC test extremely well, but I'll hold off on subjective thoughts until the design is complete and I can compare it side by side with a RAAL.

http://profesional.beyma.com/pdf/TPL150HE.pdf

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=276-440

[neildavis]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I'll post some pictures tomorrow.

This is what an unfolded and folded RT200X diaphragm look like:


The RT200X is smaller than the RT4001 that Jeff described. The RT5001 is the larger sibling. This is the unfolded RT500X diaphragm:


I used the pre-folded ESS replacement diaphragms for the larger cylindical Heil. Don't ask how it sounds, because it isn't done. You can see the large neo magnet sticking out the bottom. The magnet is actually 5 slugs glued together.



It's nerve-wracking to work on these, because I need to curve each plastic frame using a fixture that gets heated with a blowtorch. Heat the metal, then tighten the screws. It's odd using a blowtorch around a $60 plastic diaphragm, but sometimes you gotta do what you gotta do. I've got 2 assembled to the interior of the magnet structure--still need to finish two more and then assemble the outer structure.


The magnet structure is described in detail in this thread:

http://techtalk.parts-express.com/showthread.php?t=225219

It ain't DIY unless you cut your own steel :D

[winslow]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I have been using the RT-20021 for a couple of weeks now on top of some BG Neo-8Ss in my car. I think it's a perfect match. I am not missing the Scan D3004/6020s that was in there before..

[fastbike1]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I had a pair of AMT1's and absolutely loved them. "The Boss" ordered me to get rid of the monoliths when the first baby got mobile. Fortunately I had the sense not to ask if I could which went.:D

I'm very interesting in these new ones because the AMT1 still stick in my mind as filling the room with music.

Interesting. I heard the original ESS AMT3 "Rock Monitors" back in the 1970s and was very impressed. They were 3-way towers with the dipole AMT on top. I still have the brochure in my file cabinet.

[neildavis]

Re: Are you ready to try an Air Motion Transformer Tweeter?

I have been using the RT-20021 for a couple of weeks now on top of some BG Neo-8Ss in my car. I think it's a perfect match. I am not missing the Scan D3004/6020s that was in there before..

I used to have DIY Heils in all of my cars, going back to the mid-70's.

I think the next step up from a Heil is an omni-directional Heil. I've had an omni Heil in the project queue for several years now...just haven't had enough time to finish it off. But I'm going to retire at the end of the year, and start working off that long list of projects...

[winslow]

Re: Are you ready to try an Air Motion Transformer Tweeter?

Ruler flat impedance means easy crossovers. My case with the Neo-8S and the RT-2002 three components- .08mH coil, 15uf capacitance, and 1 ohm resistor wired in AR style series XO.