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Double Stack ESS AMT-1 with Wings--Possible Kit for Heritage


Chris A

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Well, looking at the measurements that Rudy has done for his stacked (two-high) AMT-1s with wings, it's clear that the two-high configuration does very well down to a crossover frequency of 450-500 Hz, which means that the AMT-1s can be used to replace the midrange+tweeter assemblies in any Klipsch Heritage loudspeaker, if bi-amping using something like a miniDSP 2x4 HD ($205 US for a stereo pair of two-way loudspeakers) to match sensitivities and do a little EQ flattening and time alignment.  The following is Rudy's implementation of a winged double high stack of AMT-1s:

 

Wings Forward.jpg

 

The two-high configuration mitigates the effect of crossing below 800 Hz in terms of harmonic distortion rise at high SPL (105+ dB at 1m), so the two-high AMT-1s with the little wings shown above will keep up with Klipsch Heritage (Khorn, La Scala, Belle, Cornwall, Heresy) in all versions (i.e., I--IV for Cornwall, I-II for La Scala, I-IV for Heresy, etc.) and years of manufacture.  The two-high, winged stack also mitigates the narrow vertical polars of the AMT-1 in that the double-height ribbon radiator doubles the vertical direct-arrival acoustic energy polar coverage field and the wings controls the spread of horizontal polars below 2 kHz down to 450 Hz.  Below is the raw (un-EQed) response of the above double-stack with wings AMT-1 assembly on-axis at 1m and at very high SPL:

 

1258935813_DoubleStackAMT-1withFrontWingsSPLandPhase.thumb.jpg.80758170e92d9589c4a81c9497c7a3ab.jpg

 

And a plot of the above measurement's harmonic distortion at 105 dB (nom):

1911837728_DoubleStackAMT-1withFrontWingsHarmonicDistortion.thumb.jpg.dc2ca68fc0ff78c09343dea8079277a8.jpg

 

And the real coup de coeur, the spectrogram of that assembly at 105 dB on-axis:

689613685_DoubleStackAMT-1withFrontWingsSpectrogram.thumb.jpg.a0d214d850c04e25fb6927ad25ec7557.jpg

 

The bumps in response at 10 kHz, and 5 kHz are due to the local rise in SPL on-axis.  Once the SPL vs. frequency is EQed flat, those two regions will show a smooth decay that's consistent with the frequencies just above and below those two areas of response rise (raw).

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A kit could be produced to do this conversion for a stereo pair of loudspeakers very easily:

 

Qty 4 -- ESS Air Motion Transformer (AMT-1) midrange-tweeter drivers (pairs wired in series for a 8 ohm loading to each midrange-tweeter amplifier channel)

Qty 2 -- wing assemblies (DIY shown above) for mounting stacked AMT-1s

Qty 1 -- miniDSP 2x4 HD DSP (to cross over to the bass bin and do some EQing/time aligning of the AMT-1s and bass bin to flatten response)

Qty 1 -- added stereo amplifier to bi-amp, with associated speaker wires and two RCA cables

 

(about $830 total assuming a bass bin amplifier is reused by the owner that is already owned, and not counting the cost of the wood in the wing assemblies)

 

The passive crossover in the loudspeaker would be completely removed from the circuit.

 

If you like the AMT sound (dipole radiator), this is a serious upgrade in sound quality.

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In the case of Klipschorns, if you are using a collared version of the Khorns with the removable top hats, the Khorn top hats can be removed so that the bass bin only is used with the double high AMT-1+wing assemblies, thus moving the midrange-tweeter drivers closer to the bass bin, and shortening down the overall height of the AMT-1/Khorn bass bin assemblies.  The sensitivity of the double-high AMT-1s with wings is extremely close to the bass bin sensitivity, and can be crossed at 450 Hz without any caveats.  In fact, the dual stack AMT-1s will be able to handle much more input power than the K-77 tweeters, and double the input power rating of the K-55 midrange to 80 w. Note the vertical scale in the REW EQ correction plot below (1 dB/division):

 

154495714_StackedandWingedAMT-1AssyPEQsfromREW.thumb.JPG.1bd4816e043fa0118ea2268e76333c75.JPG

 

EDIT:  I posted the above PEQ filters using bandwidth units--like the Xilica processors use.  If using a miniDSP, those PEQ filters use "Q" or quality factor units to specify the width of the EQ filters.  The above figure is updated below to show those filters using the miniDSP "Q" units:

774238196_StackedandWingedAMT-1AssyPEQsfromREWminiDSPQPEQs.thumb.JPG.733e76b3ad07c56999a3638a0310b1a0.JPG

 

Chris

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I suppose a description of the "why" is probably in order...

 

A single-height AMT-1 from ESS without wings has response down to 610 Hz without any modifications.  The issue with the AMT-1 in this configuration is that it begins to show phase lag below ~2 kHz, its polars widening horizontally and vertically, and experience a sudden rise in harmonic distortion above ~95-100 dB (1 m) below 2 kHz.

 

Meanwhile, there is another discussion of horn-loaded AMTs that describes the Hawthorn Audio (now defunct) "Rainier" loudspeaker which used a third party AMT with an integral horn as its midrange/tweeter driver, crossing at 350-450 Hz:

 

Rainier-Back-Angle.jpg

 

https://web.archive.org/web/20121030134740if_/http://www.hawthorneaudio.us:80/docs/RainierAnnouncement.pdf

 

https://web.archive.org/web/20140404005044/http://www.coreaudiotechnology.com/the-rainier-by-hawthorne-audio/

 

 

 

 

All this gives a clue as to what is occurring with the ESS AMT-1: it's running out of horn support at 2 kHz and lower frequencies and its polars widen, and then the diaphragm reaches the end of its available displacement at lower frequencies when played at higher SPL at lower frequencies.  So the solution to using an AMT-1 below 2 kHz is to add more ribbon support in the form a horn extension on its side walls and to double the height of the ribbon in order to give it more support in the vertical axis (and it turns out, no horn walls are needed in the vertical axis when the AMT-1 is doubled). 

 

After chasing down the AMT (with horn) used in the Hawthorn Audio Rainier loudspeaker, a full-range dipole, it became obvious that the ESS AMT-1 would also benefit by the addition of trough-type horn by adding side wall extensions and also by doubling the height of the ribbon by doubling up on the vertically--since the AMT-1 is so inexpensive at $155 each. The results are shown above, and are encouraging to say the least.

 

When it became clear that the double-stack AMT-1s with horn side walls or wings could also reach a lower cutoff frequency and also present much lower harmonic distortion levels below 2 kHz due to the added acoustic support of the ribbon(s) in both the horizontal and vertical directions, it became a no-brainer to try it.  This is exactly what Rudy did over his holidays and is what you see in the pictures.  Many thanks to Rudy for taking the ball and advancing it thus far. 

 

I see a lot of potential for this configuration in kit form to solve many complaints that Klipsch Heritage loudspeaker owners have on this forum.  The "fastness" of the horn loaded Klipsch bass bins, also described as very narrow spectrograms--indicating fast rise and particularly fast decay times relative to direct radiating woofers used in all the ESS loudspeaker models, etc., make these bass bins prime candidates to successfully mate with the winged/double height AMT-1assembly. So the Khorn, La Scala, Belle, and I suppose Jubilee bass bin (if you want to go that route) make these prime candidates for a particularly spectacular sounding hybrid dipole/horn-loaded bass loudspeaker configuration that can really knock your socks off in terms of resulting sound qualities. 

 

In addition, Klipsch loudspeakers having direct-radiating woofers are typically designed to be more efficient than other manufacturers' direct radiating woofers, and this also benefits the use of the above stacked/winged AMT-1 assembly such as the Cornwall, Heresy, or any other Klipsch loudspeaker having direct radiating woofers that extend their output into the 1-2 kHz region.  Using a stacked/winged AMT-1 assembly will enable crossing over at a much lower frequency to the woofers (typically 800 Hz or lower, if desired).  This improves the sound quality of the entire loudspeaker due to the added directivity control of the AMT-1 to lower frequencies (sort of like Palladiums) as well as providing a dipole sound that increases the apparent depth of field substantially.  The back wave can be absorbed at the stacked/winged AMT-1 assembly if it is not desired to have a dipole radiation effect.

 

In addition, the midrange polar coverage of this doubled AMT-1 with wings does not experience "pattern flip", or the loss of vertical polar directivity below 2 kHz like the stock Klipsch Heritage midrange horns.  Using AMT-1 assemblies instead will alleviate issues with floor and ceiling bounce that are problems for older Heritage loudspeakers using K-400 series midrange horns. 

 

There have been many "audiophiles" also which seek to enhance the depth of field via use of dipole-type radiators, and this configuration with its lower crossover frequency capability (down to Khorn and La Scala crossover frequencies of 400-500 Hz) brings a planar-type of depth of field and delicateness of presentation to the older Klipsch Heritage designs for those owners that are dissatisfied with their current stock or "upgraded" third party loudspeakers. 

 

The downside?  Not much if you've got the ~$830 to spring for the complete "kit", an extra amplifier lying around to power the bass bins, and a little time to knock out a couple of wooden wings (shown above) to hold the AMT-1s.

 

Chris

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On 1/2/2020 at 12:47 PM, Thaddeus Smith said:

So, presumably, these will still work really well with low listening levels?

Yes.  One of the corollaries of the high efficiency/low distortion observation that PWK made--is the realization that "the higher the efficiency of the loudspeaker, the better is sounds at very low listening levels". Very low effective moving mass of the drivers means outstanding low level listening, especially when coupled with controlled directivity of at least the higher frequencies.

 

My current application for AMTs is on my surrounding Belle bass bins in my 5.1, which means that 99.99% of the time, they are playing as echo channels for the front three (L, C, R) loudspeakers.  It's only during DVD-A music discs that make each channel an independent channel for instruments/voices, and Blu-Ray movie discs having a lot of LFE in the surround channels (in which playback distortion is probably not discernible) that the surrounds get to anything around 100-105 dB, and even then, the midrange/treble is at least 3 dB down relative to the bass bin SPL.  So virtually all the time, my surrounds do not have any issues playing well below 90 dB (1m). 

 

But I've got a pair of Khorn clones in my computer room that have been gathering dust.  If I retrofit a pair of the stacked/winged AMT-1s for the top hats, my guess is that they will completely blow away any set of Khorns that you've ever heard--because they will have:

 

  • consistent controlled directivity from 100 Hz to 20 kHz, at least 90 degrees of coverage horizontally,
  • the absence of ceiling and floor bounce,
  • flat phase,
  • vanishingly low modulation distortion even when playing very loudly (as most all fully horn-loaded loudspeakers have),
  • full time alignment of the drivers,
  • SPL vs. frequency flattened to within ±1.5 dB on-axis, and
  • the output above 400 Hz will all be via dipole radiator having almost no moving mass.

 

...all for the grand total cost of $620 for four AMT-1s and a little elbow grease in the garage to make the two wings.  I already own the DSP crossovers and related cabling and amplifiers, so this is a no-brainer. 

 

Anyone that has heard Khorns before will probably be mesmerized by the sound of these AMT-1/Khorn bass bins.

 

Chris

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1 minute ago, Chris A said:

Yes.  One of the corollaries of the high efficiency/low distortion observation that PWK made--is the realization that "the higher the efficiency of the loudspeaker, the better is sounds at very low listening levels". Very low effective moving mass of the drivers means outstanding low level listening, especially when coupled with controlled directivity of at least the higher frequencies.

 

My current application for AMTs is on my surrounding Belle bass bins in my 5.1, which means that 99.99% of the time, they are playing as echo channels for the front three (L, C, R) loudspeakers.  It's only during DVD-As music discs that make each channel an independent channel for instruments/voices, and Blu-Ray movie discs having a lot of LFE in the surround channels (in which playback distortion is probably not discernible) that the surrounds get to anything around 100-105 dB, and even then, the midrange/treble is at least 3 dB down relative to the bass bin SPL.  So virtually all the time, my surrounds do not have any issues playing well below 90 dB (1m). 

 

But I've got a pair of Khorn clones in my computer room that have been gathering dust.  If I retrofit a pair of the stacked/winged AMT-1s for the top hats, my guess is that they will completely blow away any set of Khorns that you've ever heard--because they will have:

  • consistent controlled directivity from 100 Hz to 20 kHz, at least 90 degrees of coverage horizontally,
  • the absence of ceiling and floor bounce,
  • flat phase,
  • vanishingly low modulation distortion even when playing very loudly (as most all fully horn-loaded loudspeakers have),
  • full time-alignment of the drivers,
  • SPL vs. frequency will be flattened to probably within ±1.5 dB on-axis, and
  • the output above 400 Hz will all be via dipole radiator having almost no moving mass.

...all for the grand total cost of $610 for four AMT-1s and a little elbow grease in the garage to make the two wings.  I already own the DSP crossovers and related cabling and amplifiers, so this is a no brainer. 

 

Anyone that has heard Khorns before will probably drop their dentures (due to continued gaping of the mouth while listening at any volume).

 

Chris

 

I want to hear them first, but I'll probably be selling my LS top end upgrades and go down this route. Might have to bribe Rudy for some shop time.

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3 hours ago, Chris A said:

Using a stacked/winged AMT-1 assembly will enable crossing over at a much lower frequency to the woofers (typically 800 Hz or lower, if desired).  This improves the sound quality of the entire loudspeaker due to the added controlled directivity of the AMT-1 to much lower frequencies (sort of like having Palladiums on steroids) as well as providing a dipole sound that increases the apparent depth of field substantially (which can be absorbed at the stacked/winged AMT-1 assembly if that backwave is not desired).

I have 2 pairs in boxes, and an FH-1 bin, as well as a modified FH-1 for OB use with 4 Alpha 15's. I know what I'll be doing in my basement this winter!

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10 minutes ago, Chris A said:

.all for the grand total cost of $610 for four AMT-1s and a little elbow grease in the garage to make the two wings.  I already own the DSP crossovers and related cabling and amplifiers, so this is a no brainer. 

I'm very happy with the price drop for these AMT's. I paid about $800 for 4 used ones, so getting them for $150 each is a steal!

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4 hours ago, Thaddeus Smith said:

Looks like I need to take a trip over to Rudy's Playhouse for a demo..

 

Any time sir!  Should have them hooked up and running in about 2 weeks.  Work keeps getting in the way, but just finished painting the waveguides.

 

 

paint_single.jpg

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1 hour ago, Thaddeus Smith said:

So, presumably, these will still work really well with low listening levels? That was a big factor choosing not to go with something such as the pro 396's.

 

It was the performance at low listening levels that attracted me to these strange drivers.  I ordered a pair just out of curiosity.  I still can't believe how good they sound for such an inexpensive driver.  Thanks to @Chris A, I have been able to get the driver to a place where I can comfortably cross with my bass bins and maintain a two way speaker. 

 

Originally I created a prototype which was a full horn type of device for the stacked AMT.  That configuration showed some problems and also killed the incredible open and 'airy' sound these things make.  When I removed the top and bottom, the performance returned and the sound was back to what I expected.  I now have six of these drivers for my front mains and will start my listening tests in the coming weeks.

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I’ve been a fan of this driver for many, many years. Max Potter used for his driver with his Heresys and swore by it. I’ve been speaker shopping, and have just been inclined to buy one of their finished products - but this is extremely cool. 

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42 minutes ago, Tarheel TJ said:

Rudy and Chris,

   How would you compare the sound of the AMTs to a more traditional compression driver + horn combo?  In what ways is it an improvement?  Does it fall short in any areas?  Thanks.

 

 

 

I have not used compression drivers for many years now and currently use my Oris horns, so that is what I can compare with. Although, I do have a pair of Heresys in my workshop.

 

The driver is not a perfect driver and does have some areas where it falls short.  Keep in mind that I have nowhere the expertise that Chris does, although I have been messing with horns and speakers for many years as you can see by my many builds.  These are just some of my impressions.

 

Positive:

- Incredibly 'open' and 'airy' sound compared to my very modest Fostex drivers.  This driver is an Open Baffle lover's dream!  It is OB sound on steroids.  I have built and used many OB types and styles and loved the sound as compared to horns or other drivers.  Problem is that a standard driver in an OB has some limitations. This crazy looking thing produces amazing soundstage with crisp fast, sound.  The last time I was this impressed with any speaker was when I first heard the Oris horns.  But, the Oris I heard had some very high end drivers.

 

- Based on what Chris has taught me to look for in Group Delay and Spectrogram graphs, nothing I have comes close to this driver's performance.

 

- Now that we have been able to lower the crossover point, this thing is a real winner when stacked. Although, it is plenty amazing with just a single per speaker.

 

Negative:

- It will need some EQ to get good performance below 1kHz. You can search and find folks that don't feel the driver has enough mid-range to satisfy.  However, the use of an active crossover and EQ should make that complaint a mute point.

 

- It's HF coverage is very directional, so sounds optimum if you are seated for listening vs. walking around the room  and expecting great off-center performance.

 

- If you don't have an active crossover, you will need to build a crossover for it I suspect.

 

- It needs space behind it and I don't think it will sound good if it is too close to the wall behind it since it is a dipole type of setup.

 

For me, the pluses way outweigh any negative. The sound these things make is just outrageous!  You owe it to yourself to listen to one.  1970s technology to boot!

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So if I've read through this correctly, the testing that has been done with this top end configuration will outperform the top end of everything else I have and keep it a 2 way configuration and be incredible with any worthy bass section?  I may be trying to over simplify all of the data but that's my takeaway from all of it.

5 hours ago, Chris A said:

If you like the AMT sound (dipole radiator), this is a serious upgrade in sound quality.

Never having heard "AMT sound" can anyone expand on that a bit?  Currently, my favorite rig consists of @jwc mini punch in a 3 way configuration with Faital pro HF200's on goldwood 450 horns and Daves LMAHL V2 tweeters with B&C DE10's and they sound very good.  Already have mini DSP's and plenty of amps so it's a $300 question as to weather or not it's worth it to try and improve upon the current set up.  Obviously, it would be $600 if that becomes the final (if there is such a thing) configuration for the mini punch bass bins.  

 

Some times I really hate that I joined this forum.  LOL

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4 minutes ago, Rudy81 said:

You owe it to yourself to listen to one.

So what are you doing April 2nd through the 5th?  It's an easy trip to Hope, they're easy to transport and there will be plenty of BB's to hook these up to.  

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6 minutes ago, Pete H said:

So what are you doing April 2nd through the 5th?  It's an easy trip to Hope, they're easy to transport and there will be plenty of BB's to hook these up to.  

 

Possible.  Will have to see what work has in store for me. If I can, I would be glad to take my DIY project up there.

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34 minutes ago, Pete H said:

So if I've read through this correctly, the testing that has been done with this top end configuration will outperform the top end of everything else I have and keep it a 2 way configuration and be incredible with any worthy bass section?  I may be trying to over simplify all of the data but that's my takeaway from all of it.

Never having heard "AMT sound" can anyone expand on that a bit?  Currently, my favorite rig consists of @jwc mini punch in a 3 way configuration with Faital pro HF200's on goldwood 450 horns and Daves LMAHL V2 tweeters with B&C DE10's and they sound very good.  Already have mini DSP's and plenty of amps so it's a $300 question as to weather or not it's worth it to try and improve upon the current set up.  Obviously, it would be $600 if that becomes the final (if there is such a thing) configuration for the mini punch bass bins.  

 

Some times I really hate that I joined this forum.  LOL

 

I'll let Chris handle this comparison.  Although I have owned the Faital Pro HF200's and those very horns, it was a long time ago and my 'audio' memory is not long lasting.  Chris has more gear similar to what most Klipsch aficionados own. FWIW, my wife who appreciates good sound, but is not 'into' it came in to the media room while I was doing A/B testing with my Oris vs. a single AMT. I asked her to sit and listen and give me her impressions.  After just a couple of minutes, she looked at me and said "that's a no brainer and left".  Mind you, she had been ribbing me over even contemplating selling my Oris.

 

I'm honestly perplexed and can't understand why more people have never heard of this AMT thing.  I never would have known had Chris not used that driver to help explain some measurements he was teaching us to make.

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On 1/2/2020 at 2:35 PM, Tarheel TJ said:

How would you compare the sound of the AMTs to a more traditional compression driver + horn combo?

The dipole effect of opening up the sound (i.e., artificial depth of field) can be breathtaking. 

 

It is wise to remember that this Magnepan or MartinLogan type sound is not in the original recording, however.  Some don't think twice about this and welcome the added soundstage effects (including a perception of lightness of sound and extreme speed of the tweeter), but I oftentimes desire my sound to be as accurate to the recording as I can get it.  It is quite easy to kill that backwave by "stuffing a sock in it", so to speak, on the backwave side to absorb the rear wave. 

 

But on the surrounds where I have the AMT-1s currently positioned on top of Belles, that extra amount of backwave sparkle is actually very welcome, since the job of the surrounds are to provide an added sense of depth and immersion. 

 

In terms of polar directivity up high--it's actually pretty good.  What's not good is the vertical polar coverage, which was the driving reason for suggesting a two-stacked AMT instead of just one.  It turns out that the two-high stack also is a significant contributor toward lowering the cutoff frequency from 610 Hz to 450 Hz.  I did a polar sonogram in-room on a single AMT-1 on top of a Cornwall bass bin in a pretty noisy environment (as you can see below in the polar sonogram).  Everything above 650 Hz is the AMT-1, which actually shows that the horizontal coverage on centered level axis is actually very good out to 45 degrees off the central axis (i.e., 90 degrees of coverage)--all the way up to 20 kHz and beyond (where the measurement sweep amplitude was closing down just as it gets to 20 kHz, as you can see in the plot below):

 

2114005964_CornwallAMT-1normalizedpolarplot(3D).thumb.jpg.66437aa33dec8708d3cc2b83a627abfe.jpg

 

 

So the real Achilles heel of the driver itself is very narrow vertical directivity.  However, I expect the two-stack AMT-1s with wings to be much better in this regard (in terms of increasing the vertical band of direct arrival coverage in-room, rather than the single height AMT-1). 

 

I checked the on-axis spectrograms of the TAD TD-4002 and the BMS 4592ND against the AMT-1, and they are pretty much dead even in terms of their internal damping characteristics, but the AMT-1's backwave reflecting off the wall usually distracts the listener into thinking that these have a long decay tail.  They don't have a long decay trail--in fact, it is quite fast.

 

So to sum up: I actually think that the AMT-1 has no other downsides than the narrow vertical coverage, mentioned above.  In fact, it's performance above 10 kHz is at least as good as the TAD  TD-4002 and the BMS 4592ND--which is the discriminator for other less expensive compression drivers, especially those with titanium diaphragms.

 

On 1/2/2020 at 2:54 PM, Pete H said:

So if I've read through this correctly, the testing that has been done with this top end configuration will outperform the top end of everything else I have and keep it a 2 way configuration and be incredible with any worthy bass section...?

This may be true depending on what you're talking about that you already own, and it is true that you can keep it two-way if using a stacked/winged AMT-1 assembly, even for a La Scala or Khorn.  But remember that the caveat is that it will be bi-amping using a DSP crossover. I would not presently advise anything passive.  There are just too many downsides to them, and the time spent on trying to get everything balanced against the bass bin output would likely be excessive.

 

On 1/2/2020 at 2:54 PM, Pete H said:

Never having heard "AMT sound" can anyone expand on that a bit?

If you've ever heard planar dipoles in-room (such as MartinLogans or Magnepans), you've pretty much got the AMT sound in your mind's eye.  In fact, the AMT-1 is even a bit more convincing, in my opinion, since it has so much more dynamic range than a planar dipole of any configuration.

 

On 1/2/2020 at 2:54 PM, Pete H said:

...Obviously, it would be $600 if that becomes the final (if there is such a thing) configuration...

🤣

 

Chris

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