Do you like AMT tweeters?

[Stokdoof]

The ones I've heard have been very nice sounding, but do seem to lack a certain bite or sharpness (compared to a waveguided metal dome, for instance). They don't quite seem to convey the reality of sound to the same extent, seems a bit too good, if you know what I mean.

What are your thoughts on AMTs?

AMT = ASR Measured Tweeter ?

 

[Digby]

Air Motion Transformer - Wikipedia

en.wikipedia.org

 

[fpitas]

One moderately expensive speaker (low four figures) was the Hedd 07 mk2. It has adjustments on the back for tweeter brightness. I could get it bright enough, even too bright, but it didn't sound just so. There was something a bit, I dunno, "flat" about the presentation. It sounded nice, but when it was supposed to sound harsh or aggressive (as denoted by the music), it couldn't do it.

I've never played with those. But I will say, in voicing my own speakers, it's been more than possible to achieve that (undesirable) effect.

 

[617]

Fundamentally there is nothing that unusual about AMTs - they are small format, generally low-power high frequency transducers. At a given price point, they are a little worse than good dome tweeters, but this can probably be explained by the fact that they are a less mature, more complex technology.

Most of their sound differences can be explained by:

• Size: the radiating area of most AMTs is larger then a dome tweeter. Large size = narrower dispersion
• Distortion: probably not very audible, but if a small AMT is used lower down, it will distort more
• Marketing. AMT's have a distinctive appearance which incentivizes designers to use them. They then need to 'highlight' this technology by running the tweeter a bit hot, or otherwise shaping the frequency response.

In a good design not overly constrained by cost or 'showroom sound', the only factor that really matters is the first. In a 3 way, with a small AMT, the differences between the AMT and a dome will be minimal. In a large 2 way, with a huge AMT, the sound will be somewhat distinctive due to the wide horizontal and narrow vertical radiation. The former is still a viable design, but using a big AMT in a big two way is not really a state of the art design in 2022.

The 'crossover' used doesn't make a difference, really. Same tradoffs with a dome tweeter (or ribbon.) Impedance and stuff like that is different, but that doesn't matter much, or matter at all in an active crossover. Cross low and you get potentially smoother directivity match with a woofer at the expense of higher distortion due to LF excursion for the tweeter. Cross high for more output but greater directivity mismatch.

The narrow dispersion is not a bad thing, and I like the use of AMTs in small monitor speakers such as those from ADAM.

The one potentially unique feature of the AMT is that they are dipoles but I don't know of any commercial speakers using them this way, and the best dipole designs seem to rely on forward/backward facing domes (or various planar drivers.)

 

[Digby]

I've never played with those. But I will say, in voicing my own speakers, it's been more than possible to achieve that (undesirable) effect.

I don't mean that you run from the speakers, just that it accurately reproduces the, how would you say, violence/aggression/turbulence of the particular passage in the music. The rest of the time, as dictated by the music, it doesn't sound that way.

I am loathe to use the term dynamic, as I will get told off for using it wrongly, but perhaps a broader ability to represent the swings of music. I felt like the peaks were too reserved/constrained for my liking with AMTs, turning up the dial on the back didn't help, then I had extra brightness (tizz), but not extra forwardness (if these subjective terms do any justice to what I am trying to say).

 

[fpitas]

I don't mean that you run from the speakers, just that it accurately reproduces the, how would you say, violence/aggression/turbulence of the particular passage in the music. The rest of the time, as dictated by the music, it doesn't sound that way.

I am loathe to use the term dynamic, as I will get told off for using it wrongly, but perhaps a broader ability to represent the swings of music. I felt like the peaks were too reserved/constrained for my liking with AMTs, turning up the dial on the back didn't help, then I had extra brightness (tizz), but not extra forwardness (if these subjective terms do any justice to what I am trying to say).

Surprisingly small changes in the shape of the frequency response curve can make a big difference, depending on the track.

 

[puppet]

I use the older (original) heil in a 2 way design over a 15" woofer (Faital 15pr400) crossed around 840hz. The design is active DSP (EV DX34a) For the last dozen years or so I've worked with that particular AMT I've found this design to work best for me. I fabricated a wave guide for it which allows for the lower cross over. Any lower and these particular diaphragms (newer offerings from ESS) will start to distort with elevated second and third harmonics. Interestingly, a 4th order filter applied as a lo-pass will yield an 8th order acoustic response. Down low, the diaphragms natural roll off gets pretty steep.

I can't really tell through FR measurement or actual listening where the crossover is. The two drivers blend nicely. The Heil can take a lot of power as well. I often drive the system to very realistic SPL's and they are clean w/distortion levels typically -50db. The older housing design uses the focus plates to compress the output somewhat making these a bit more sensitive and highly efficient.

As was stated above, handling the rearward output is important. I've found that some attenuation in the form of insulation and thin foam applied to the back changes the forward FR. My thinking is the added resistance influences the diaphragm positively or negatively. Finding the right thickness combination does help to yield a better overall FR. Mundorf does something similar I believe. No doubt Mundorf is state of the art for AMT's these days.

For home HIFI these are a nice compromise for those that don't necessarily want to go down the CD/horn trail.

 

[2020]

I've only used AMT 1 time in a completely rather than ideal scenario, so my opinion is moot, but I go based off this post when I think of them now: https://forum.audiogon.com/posts/1815634 (I have edited this quote)

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 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.

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.

Nearly every AMT tweeter I've seen looks like it has really tight vertical dispersion and this kills them to me, so I think they should be stuck on a substantial waveguide to improve this. I hate having a tight sweet spot and am sensitive to it. Humans move, speakers should take this into account.

 

[Jim Shaw]

I have a pair of desktop monitors with AMTs. [Now, that's a small sample.] I have mixed emotions about them. I say, use them to suit your hearing and program material. Mine do not become annoying over the long term, as horns surely do. Some simple observations:

1. They seem effortless at reproducing very high frequencies. But, by not going very low, they strain the design of the other system drivers, eg: mid-woofers may have to play to higher frequencies than optimal. And adding another mid-range driver really complicates the system, especially interference.

2. They seem to NOT color high frequencies, which is evidenced in other types of tweeters by designers laboring to decide from a range of different dome materials. I don't think the measuring state-of-the-art provides a reliable and repeatable measurement of tweeter coloration. Yet coloration is a major factor in subjective evaluation. Some call it "timbre." I think human hearing may be more aware of timbre than numbers suggest.

[Feel free to argue amongst yourselves. Hard data seems scarce.]

 

[Chromatischism]

• Marketing. AMT's have a distinctive appearance which incentivizes designers to use them. They then need to 'highlight' this technology by running the tweeter a bit hot, or otherwise shaping the frequency response.

This is also my experience. Most of them seem to be made that way. It seems most speaker makers are afraid to perfectly integrate an AMT because then the cat would be out of the bag and people would wonder why they are paying more for something "exotic" when they can't hear a difference.

 

[mhardy6647]

AMTs are OK. Never been a favorite of mine for treble reproducers, either way back when (Heil) or now today. Today we have a proliferation of generic AMT designs at all price points (for better or worse).

 

[2020]

I love the extremely wide range of reactions. Not just even good or bad, the in-betweens. What can we even conclude from this?

 

[mhardy6647]

I love the extremely wide range of reactions. Not just even good or bad, the in-betweens. What can we even conclude from this?

Probably a roughly Gaussian distribution, with a mean of meh.
Not unlike our (late) puddy cat, Zappa.
Zappa was grey on the average.



I guess the SD would be interesting to calculate.
(for AMT preference, that is, not Zappa)

 

[morpheusX]

Beyma TPL-150H is an amazing AMT used in several high-end designs.

I've used them in my DIY speakers, and they are extremely detailed without sounding fatigated.

Here's a GP measure, including distortion figures @ 100db:

 

[tw 2022]

I've never heard one which properly integrates with a cone bass-mid driver. There always seems to be some added 'tinsel' on top, more than a well integrated dome/cone can do...

my guess is that you haven't heard a @Dennis Murphy amt design yet.. i have , in my living room... the emotiva b1 mod he did... it works, well......

 

[Chromatischism]

Dennis isn't running a show room and cares more about you getting affordable accuracy.

 

[617]

I love the extremely wide range of reactions. Not just even good or bad, the in-betweens. What can we even conclude from this?

There is one correct conclusion. They are okay, but for a given price point, tend not to be as good as a dome tweeter, but have niche applications where specific units make sense.

Jim Holtz and Kurt Campbell have a speaker called the Bordeaux which uses a fairly substantial AMT. Why? Because the combination of tight vertical directivity and low distortion which came from this tweeter melded with the semi-dipole operation of the mid-range in that design. Is it a cost effective way to build a speaker that will sound good to everyone in every room? No, but I bet those speakers sound incredible.

Long story short they're just direct radiators like ribbons and domes and almost everything else.

There's only one modern driver technology which does something remotely interesting and which has had any real-world impact - the balanced mode radiator. Someone correct me if I'm missing something.

 

[tw 2022]

Dennis isn't running a show room and cares more about you getting affordable accuracy.

Dennis is good at what he does, and he's less concerned with maximizing profit than putting out a good product... Another little secret: he offered to do it unsolicited.. That about says it all.. He's a good guy....

 

[Anonamemouse]

I have these ones in my dipole system and think they are absolutely fabulous.
They do require being in a three way to really do their job well though

 

[sfdoddsy]

I love AMT's in my limited use with them. I built a 3 way box with a B&G Neo PDRW and I love how it sounds. It disappears more than Ribbons that I have used. Ribbons often add nice sizzle and even though I like that, it doesn't sound as natural. High quality domes are great but don't seem quite as transparent as the AMT's. But I do think that the design and crossover has a lot to do with it. The way in which the AMT is mounted in the box can greatly change it's characteristics, which can make it challenging to design a crossover for. Plus, you have to consider how well any of these speakers fit in a given room. There are a lot of variables at play. I love mine though and my next design will incorporate some Mundorf AMT's.

The Neo is very good, but it isn't an AMT. It is a planar magnetic. I've had both the Neo and now an AMT (AST2560, same as the Bordeaux) in my DIY speakers and slightly prefer the AMT both objectively and subjectively.

Not sure if they are better than regular tweeter, but I run them dipole.