Do you like AMT tweeters?

[Frunse]

I got my AMT25 Waveguide to the right spot and i guess i could use it from 1,8kHz with an Steep FIR Filter.
Here the Image with an 3,3uF and 4,7uF in Series!!!:

And here distortion with 3,3uF:

What do you say anything that i could do better??? Any Suggestions??? What happen if i shorten the Waveguide 10 or 20 mm on the Front???

For Now it is 78mm deep!

The Link for the whole Story you find above.

 

[Waxx]

I wonder why nobody thinks about MEH (multi entry horns) like the Danley Labs Synergy horns. That principe is patent free since a few years and can be done with all kind of drivers. Most use a compression driver as tweeter and smaller drivers for the rest. It keeps (when done right) everything within the passband of the horn in a constant directivity and works as a single point source like a fullrange driver, but without the limitations of those. It's what people i rate high in speaker design are studying now more (also on diyaudio) to solve directivty and phase issues in classic speakers.

(design: Scott Hinson. Build: Randy Parker. Source: DIY Loudpeaker PAD @FB)

Combine this with a (few) subs and you have what most search, constant in directivity and true point source, but with multiway. crossovers are dsp mostly for this kind of systems. This is not commercial availeble but from Danley Labs (targetted at pro audio) but there is no legal limitation to commercialise it as the patents are expired.

This will be hard to do with most AMT's, but could work with CD's and domes. The horn is actually a waveguide, not a real horn.

 

[Audionaut]

I wonder why nobody thinks about MEH (multi entry horns) like the Danley Labs Synergy horns

I find the speaker and its features very interesting, Waxx, but I think it's a bit out of place in this thread.

 

[Frunse]

Please show me Step Response , Frequency Response and so on, Is it working with an AMT????
What about Hornrsonances Non Linearitys ???

I dont Like Horns!!! for Home Hifi @ al , sorry never i have listen to an Hornspeaker and was satisfied, they most time Harsch and Agressive and sure Loud \o/

 

[Arindal]

What do you say anything that i could do better??? Any Suggestions??? What happen if i shorten the Waveguide 10 or 20 mm on the Front???

Measurements look excellent, and the concept is very promising.

I would not shorten the waveguide if there is no practical necessity to do so. As mentioned, these medium-diaphragm-area AMTs tend to open up in dispersion angle towards lower frequencies pretty quickly. The more you control that with the waveguide, the better.

Having quite some experience with AMTs, I would never give an advice solely based on measurements and geometry. My no. 1 recommendation would be to listen to as many recordings with vocals, spoken word and cymbals as possible trying to find an ideal EQ tuning for the treble region. Most of AMTs require a little bit of increasing level on axis above a certain frequency in order to compensate for narrowing directivity in and achieve balance in the room.

I wonder why nobody thinks about MEH (multi entry horns) like the Danley Labs Synergy horns.

I guess a lot of people are thinking about it, but can tell you from own experience that combining an AMT with a more or less trapezoid or linear horn/waveguide shape is the most difficult thing to do. As mentioned, the wavefront is rectangular, even and pretty big compared to the wavelengths. You can run into all sorts of resonances, horn colorations, interference and edge diffraction issues without noticing it. My guess would be a compression driver with very small chamber opening is much easier to handle.

Typical waveguides for AMTs, on the other hand, are often just controlling the horizontal pattern while taking advantage of the more or less linesource-like vertical dispersion.

 

[Waxx]

I guess a lot of people are thinking about it, but can tell you from own experience that combining an AMT with a more or less trapezoid or linear horn/waveguide shape is the most difficult thing to do. As mentioned, the wavefront is rectangular, even and pretty big compared to the wavelengths. You can run into all sorts of resonances, horn colorations, interference and edge diffraction issues without noticing it. My guess would be a compression driver with very small chamber opening is much easier to handle.

Typical waveguides for AMTs, on the other hand, are often just controlling the horizontal pattern while taking advantage of the more or less linesource-like vertical dispersion.

But then you get in trouble with matching it to a cone mid, because the center to center distance is to big. While when you use the MEH principe on that horn it may work better as the center to center distance is much smaller. The mid driver can be on each side of the horn, but get good pattern control trough the horn. I'm not skilled enough to make this work, but i think i understand enough to see that that could work, but i see nobody with the skills trying it.

 

[Audionaut]

I'm not skilled enough to make this work, but i think i understand enough to see that that could work, but i see nobody with the skills trying it.

The question is why, when there are solutions that work.
I have installed the Beyma TPL-200/H twice and was very satisfied both times.

Test Bench: Acustica Beyma TPL200/H Pro Sound Air Velocity Transformer

In this edition of Test Bench, Vance Dickason characterized a different high-frequency transducer: the TPL200/H, a horn-loaded pro sound AMT from the Valencia, Spain, company Acustica Beyma. The TPL200/H is one of the Air Motion Transformers (AMT, aka AVT Air Velocity Transformer) that Beyma has...

audioxpress.com

 

[Frunse]

The question is why, when there are solutions that work.
I have installed the Beyma TPL-200/H twice and was very satisfied both times.

View attachment 455383

Test Bench: Acustica Beyma TPL200/H Pro Sound Air Velocity Transformer

In this edition of Test Bench, Vance Dickason characterized a different high-frequency transducer: the TPL200/H, a horn-loaded pro sound AMT from the Valencia, Spain, company Acustica Beyma. The TPL200/H is one of the Air Motion Transformers (AMT, aka AVT Air Velocity Transformer) that Beyma has...

audioxpress.com

This was inspiring me to build an Waveguide for my AM 25, specialy at the very high Frequencies this TPL Waveguide Compo fall apart, i guess it is because of the Length of that Beyma AMT.

And the Price is also not DIY friendly ....LOL

also 100dB isn't something you realy need on Home Hifi and not easey to find an good Middriver for this too.

My Kombination with two 18W8434G00 (MTM Parallel) would reach the 95dB of the harwood AMT25 i guess. (two Parallel (4OHM) on one Front must be +6dB right)

 

[DavidMcRoy]

Both attenuating floor/ceiling reflections and keeping directivity index high are in general excellent ideas for home listening. But I found linearly attenuated reflections and reverb to be the most helpful. D´Apollito-style arrangements with a rather high x-over freq tend to show a medium-width dip caused by interference/lobing.



You mean the AMT allows 1.5k of lowest x-over point? May I ask what was the issue with this one choice?

In terms of vertical lobing, this from a theoretical point is surely the best way to go, and with two midrange drivers I would not overly worry regarding localization issues.

It often leads to a problem with directivity index, though, as most of broad-diaphragm, medium-height AMTs tend to have a steeply decreasing directivity index below 2.5k towards lower frequencies (as width and height get increasingly small compared to wavelengths). So crossing around 1.5k brings a lot of energy into the room between 1.5k and 2.5k making it sound very direct, present, bringing overly bright formants and shiny vowels, if that makes sense. This has to be addressed somehow, either with a waveguide, some directivity control via midrange driver, a slight additional on-axis dip, or whatever measure.

I am familiar with those issues and they have been addressed with an improvised waveguide, although you don't see it in the first photo:

 

[Frunse]

I am familiar with those issues and they have been addressed with an improvised waveguide, although you don't see it in the first photo:

View attachment 455569

You realy need to get some nice Allen Srews Man ....

For that, i use always this for my Driver:

on the back Side
Easier to get the right srew than.

 

[Arindal]

You realy need to get some nice Allen Srews Man

Torx is also your best friend!

Fully agree, these drive-in nuts or hammer-in nuts are the best!

 

[2020]

How good are the Adam AMT tweeters? View attachment 454868

People generally like them And remark that they are non-fatiguing. However Autumn does voice them a bit brighter or at least tilted which may cause people to not like the presentation of them.

Additionally, the original inventor of Adam Audio has a new company called HEDD, and I've seen multiple people say it sounds noticabley different. The HEDD tweeter is drier and softer, whereas the ADAM tweeter is harder and more "digital" sounding.

But it's all a continuum; one person will think the soft tweeter sounds more "natural", but for another person it may not have enough bite. I think it is nice to know that they can be potentially voice differently without having to audition them yourself.

 

[DavidMcRoy]

People generally like them And remark that they are non-fatiguing. However Autumn does voice them a bit brighter or at least tilted which may cause people to not like the presentation of them.

Additionally, the original inventor of Adam Audio has a new company called HEDD, and I've seen multiple people say it sounds noticabley different. The HEDD tweeter is drier and softer, whereas the ADAM tweeter is harder and more "digital" sounding.

But it's all a continuum; one person will think the soft tweeter sounds more "natural", but for another person it may not have enough bite. I think it is nice to know that they can be potentially voice differently without having to audition them yourself.

If they really sound different, it means they have a different frequency response and/or a different distortion profile. (Just like anything else.) As a group, AMTs seem to have low overall distortion.

 

[Arindal]

If they really sound different, it means they have a different frequency response and/or a different distortion profile.

Neither is the case with the majority of AMTs. You can EQ them to perfectly identical anechoic response and keep them well under heir threshold of producing audible distortion, they nevertheless can sound very very different. As they show no tendencies for resonance and compression issues as well as breakup (which is IMHO the main reason they in general tend to sound non-fatiguing and detail-resolving alike), it leaves basically two explanations for the very different sound:

directivity - although they do not have diaphragms following a pistonic movement concept, they nevertheless produce a pretty perfect even wavefront of rectangular pattern. As a matter of consequence, directivity pattern is highly dependent on diaphragm geometry and frequency. The transition between broad dispersion at lower frequencies thanks to diffraction and increasing tendency to narrow dispersion, is pretty suddenly, pretty angle-dependent and in most cases (as most of them are not quadratical), differing for vertical and horizontal behavior. In my understanding the reason why it is so difficult to design proper waveguides affecting both dimensions.

even response over a listening window - it is more or less a consequence of the same phenomenon. The closer you get to the frequency they start to narrow down dispersion, the response at angles being inside the window of even wavefront´ and those outside tend. to drift away forming pretty funny pattern. At this or that frequency, your listening window might touch this or that window of such behavior, resulting in pretty much unpredictable consequences for the perceived response.

As most of AMTs are tweeters with a more of less standard frequency range, their diaphragm dimensions vary between horizontal and vertical, but are tending to be bigger than comparable domes, you have pretty much all of the aforementioned effects well within the frequency bands defining sound quality.

To give you a visual impression of what I mean, this is a bunch or FR graphs at different angles (vertical) for one of the rather high AMTs:

Don´t get me wrong - this is IMHO one of the best AMT on the market in terms of sound quality. It is just an illustration of what any loudspeaker designer has to take into consideration, and in many cases this will lead to non-standards methods of optimizing tonal balance and combining it with a midrange.

Tonal issues differing over a narrow listening or measuring window might be also the reason why AMTs are attributed different sound characteristics. I never really experienced one sounding harsh or hard. If such impression occurred, it could be tracked down in most of cases to a narrow frequency band being overrepresented, so highlighting events in the recording which cause harshness. A sharp notch filter might fix this.

 

[Frunse]

To give you a visual impression of what I mean, this is a bunch or FR graphs at different angles (vertical) for one of the rather high AMTs:

And the longer they are the more Problems they get on Vertikal Angles right?!

How it is with MTM Konfiguration (Dapolito)?
can we say the shorter the AMT the better they work there ? So better use an short AMT with Waveguide than an 160mm Long Munddorf without Waveguide ???

You Ears need to sit at the AMT hight, so your are in the right listening Position.

 

[Audionaut]

And the longer they are the more Problems they get on Vertikal Angles right?!

The radiation behavior changes.
Desired by some, a problem for others.

 

[Arindal]

And the longer they are the more Problems they get on Vertikal Angles right?!

It is safe to say that the longer the AMT, the lower the frequency the problems and transition towards line source behavior start. But I would not support the claim of ´more problems´ coming with length, as a long AMT might also shift the tipping point, i.e. the sudden transition from wide dispersion to narrowing one, towards lower frequencies, hence far away from horizontal dispersion problems, if we are talking about a rather narrow diaphragm shape.

The directivity imbalance between lower octaves and how they behave at shorter wavelengths, I would see this as the main reason why it is so difficult to handle AMTs. and with the standard sizes of 4...8cm in height and a ratio of less than 2:1 (height:width,) directivity problems tend to pyle up within one octave, and increase in directivity index is too sudden and overly steep. In my understanding the main reason why many AMTs sound bright in some concepts.

Personally I would say long and narrow AMT is easier to handle, if you deal with horizontal dispersion issues separately, for example designing a waveguide.

can we say the shorter the AMT the better they work there ?

Guys from a German webshop offering DIY kits have been trying the 16cm AMT in such a concept:

Sofia AMT12 is the name, maybe someone has listened to is and can tell you more. Definitely an unusual concept as the x-over freq supposedly cannot be brought lower than x2K, so I would expect the two midrange drivers being some 40cm away from each other, to do pretty interesting things. Bringing the two closer to each other with the help of a smaller AMT, in theory would reduce lobing and interference problems. On the other hand, you are more likely to have too much off-axis energy in the AMT´s lowest octave playing more or less alone. A phenomenon which is even slightly audible with the Finkteam Kim, employing the more forgiving 11cm version of this AMT and some pretty clever x-over design.

From directivity and compromise point, I guess a triple strategy works best on paper: countering the AMT´s uneven horizontal dispersion with the help of a waveguide, getting the x-over frequency to the lowest point possible, and doing something with the midrange drivers to keep the directivity constant at lower octaves. The latter is in my understanding a reason why MTM dipoles or midrange line arrays are such a good match with bigger AMTs. Their directitivity and subjective dynamic behavior is very much alike, and the virtual coax does add coherent imaging.

 

[Frunse]

It is safe to say that the longer the AMT, the lower the frequency the problems and transition towards line source behavior start. But I would not support the claim of ´more problems´ coming with length, as a long AMT might also shift the tipping point, i.e. the sudden transition from wide dispersion to narrowing one, towards lower frequencies, hence far away from horizontal dispersion problems, if we are talking about a rather narrow diaphragm shape.

The directivity imbalance between lower octaves and how they behave at shorter wavelengths, I would see this as the main reason why it is so difficult to handle AMTs. and with the standard sizes of 4...8cm in height and a ratio of less than 2:1 (height:width,) directivity problems tend to pyle up within one octave, and increase in directivity index is too sudden and overly steep. In my understanding the main reason why many AMTs sound bright in some concepts.

Personally I would say long and narrow AMT is easier to handle, if you deal with horizontal dispersion issues separately, for example designing a waveguide.



Guys from a German webshop offering DIY kits have been trying the 16cm AMT in such a concept:

View attachment 456084

Sofia AMT12 is the name, maybe someone has listened to is and can tell you more. Definitely an unusual concept as the x-over freq supposedly cannot be brought lower than x2K, so I would expect the two midrange drivers being some 40cm away from each other, to do pretty interesting things. Bringing the two closer to each other with the help of a smaller AMT, in theory would reduce lobing and interference problems. On the other hand, you are more likely to have too much off-axis energy in the AMT´s lowest octave playing more or less alone. A phenomenon which is even slightly audible with the Finkteam Kim, employing the more forgiving 11cm version of this AMT and some pretty clever x-over design.

From directivity and compromise point, I guess a triple strategy works best on paper: countering the AMT´s uneven horizontal dispersion with the help of a waveguide, getting the x-over frequency to the lowest point possible, and doing something with the midrange drivers to keep the directivity constant at lower octaves. The latter is in my understanding a reason why MTM dipoles or midrange line arrays are such a good match with bigger AMTs. Their directitivity and subjective dynamic behavior is very much alike, and the virtual coax does add coherent imaging.

At the Red Cirkel it looks a bit strange.
The Crossover wont work right or the Mid driver has an Problem because of that MTM Distance between the Middriver.

 

[Arindal]

At the Red Cirkel it looks a bit strange.

That is horizontal 30 and 45deg? Looks like what I would expect from a pair of slightly bigger midwoofer cones. Vertical would be interesting.

 

[Frunse]

What about such crazy looking Design ?

Probably no Baffelstep Problem @ all too

I want to test this kind of Box: