Are you ready to try an Air Motion Transformer Tweeter?

[CUtiger]

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

Thanks Jeff, not all that bad for a limited application scope I guess but disapointing none the less. I am planning a three way with the morel cam558 dome mid and I suppose with some stretching this could be made to work. I really wanted to use a non-dome tweeter in this build, just because. Based on those graphs I think my task will be made easier by the neocd1.0, or possibly go with the larger airborne but now I'm in a higher price bracket. The measurements of the latter suggested they may offer better dispersion characteristics relative to the mid with a lower crossover point but the dropoff to its smaller sibling is larger than I expected.

[winslow]

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

Maybe I should bump them up to 6k...

But these little AMTs were just enough crack to get me wanting to try some bigger ones in an 8" two way.

[Jeff B.]

Re: Measurements of the Airborne RT-20021 AMT

5k? That's a little disapointing was hoping it would be good down to at least 4k, with that in mind I may opt for the small fountek ribbon. Can you post the measurements?

Here's the frequency response of the Airborne RT-20021 AMT tweeter, -10dB by 4khz.


Here's the Distortion plot - not really all that bad, once I looked at it again. It's mostly -50dB in its operating range, but not as good as a lot of other tweeters out there.

[winslow]

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

Been running RT20021s with Neo-8Ss in my car for 4 months or so. They are crossed at 5k and up.

[dlneubec]

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

I have a pair of Aurum Cantus AST2560's on their way that should arrive this week. I might have a chance to do some IB type measurements next weekend.

I'll start a new thread on them when I get some measurements, just so the results are easy to search for and find and post a link here.

[neildavis]

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

For me the Airborne RT20021 has much more limited usefulness compared to its bigger sibling

All depends on what you are trying to accomplish. I've been using Heils for many years, but was always disappointed by diffraction issues due to the large radiating area. The smaller RT20021 could open up some new possibilities for more non-directional designs.

I've still got a test fixture I used to switch over a 2-1/2" tall Heil to a very small dome (3/8") at 6K using an 8-pole active crossover. It's interesting to hear how the non-directional position of the switch has more "spaciousness" and is much less fatiguing to listen to.

I'll be using the Eton 3" mid, so I was hoping that the published frequency response curve for the RT20021 was correct. If it only goes down to 5K I might have a problem.

Of course, If I need more excursion I could always use the larger diaphram with a small magnet structure, like what's in the picture below. Notice that only part of the diaphragm is in the magnetic field. The part that is not in the magnet structure has a special name: it is called a "resistor" :D

[gowa]

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.

I owned a set. Big ESS fan.

[CUtiger]

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

5k? That's a little disapointing was hoping it would be good down to at least 4k, with that in mind I may opt for the small fountek ribbon. Can you post the measurements?

[Jeff B.]

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

At the bottom of the faceplate, at the diagram, the opening is 20mm x 18mm. The opening in the faceplate is beveled, and at the top the opening is 25mm square.

I got the Eton 3" mids to go with these. Should be a nice combination. Probably won't start working on them for a while--got several other projects ahead of it.

For me the Airborne RT20021 has much more limited usefulness compared to its bigger sibling. When I measured the frequency response of it, it dropped off very rapidly below 5kHz. Distortion rose pretty quickly below that too. It's going to need a small midrange or mid-tweeter to work well.

Jeff

[neildavis]

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

Thanks Neil, I'll be awaiting your impressions after you get a chance to get them out of the box. Quick question are they really as tiny as listed, the PDF is hard to read but looks like the frame is 75mm? Need a tweeter to pair with a dome mid and was previously looking at the neocd1.0 but this has got me interested.

At the bottom of the faceplate, at the diagram, the opening is 20mm x 18mm. The opening in the faceplate is beveled, and at the top the opening is 25mm square.

I got the Eton 3" mids to go with these. Should be a nice combination. Probably won't start working on them for a while--got several other projects ahead of it.

[CUtiger]

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

Thanks Neil, I'll be awaiting your impressions after you get a chance to get them out of the box. Quick question are they really as tiny as listed, the PDF is hard to read but looks like the frame is 75mm? Need a tweeter to pair with a dome mid and was previously looking at the neocd1.0 but this has got me interested.

[neildavis]

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

Edit:

Nevermind found it, always forget about our friends north of the border.

Meniscus carries the RT20021--they just don't have them listed on their web site yet. Got two for Christmas, and when I enquired they had a total of 4 but where planning to get more.

Mine are still in the box. Looked at them, but that's as far as I got.

I think there is a lot of potential in using small Heil drivers that still hasn't been explored. I made a "mini-Heil" over 35 years ago, and I've been interested in getting back to explore that potential ever since.

[CUtiger]

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

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

Where can one find this model? The only thing I see listed at meniscus is the 4001.

Edit:

Nevermind found it, always forget about our friends north of the border. Now a better question has anyone measured / listened to one, hoping it is similar to its brother in this thread.

[JimHRB]

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

Anyone got any progress to report on using these?

[neildavis]

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

I have a stack of these still here-

http://www.kjmagnetics.com/proddetail.asp?prod=DC2

The DIY AMT might be fun to try.

There was an article about 35 years ago in Audio Amateur that described several different magnet structures, but with strong neo magnets there are a lot more possibilities. Someday I may update that article. The grade 42 magnets you bought are just the right thickness for a very simple magnet structure that doesn't require too much metal work.

A rather poor scan of the original article is at this link: http://www.audiodevelopers.com/misc/AA_article/

Jeez, who in their right mind would still be making DIY Heils after 35 years? Uh oh :o