Conversation Starter - X Series AMT & Waveguide Driver

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Desertpilot

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Now that many of our members who regularly post have one of the X series models, I thought a thread dedicated to discussing the AMT & Waveguide driver would be helpful.

My understanding:
--Clayton says that this particular AMT driver is one of the best available (he hinted that there are lots of cheap "knockoffs" out there).
--My understanding is that he crosses over the driver at 1,000 Hz.  I'm sure there is a roll off involved to the mid-range driver.
--He employs the waveguide for "controlled directivity".

My research:
--A felt strip is used behind the driver to preserve the open baffle concept.  It is critical because mid and low frequencies will come into the rear of the driver causing chaos.  Some designers use a hard shell cap instead.
--The AMT design (moving similarly to an accordion) moves 4 times as much air as a dome tweeter.

My experience with my X3s:
--The AMT driver reproduces sound, in my opinion, much more realistically than a dome tweeter.  Especially horns, violins and female vocals.
--Clayton's design blends the AMT beautifully with the mid-range driver.  In other words, male (mid-range) and female (AMT) vocals sound natural and fully balanced.  No noticeable shift between drivers.
--The AMT is a complex mechanical structure.  Break-in is essential.  The more hours I get on my speakers, the better the AMT driver sounds.
--Brightness can be controlled through both break-in and shifting toe-in.  In fact, changing toe-in an inch at a time will produce noticeable results.

Choosing between the M series with a dome tweeter and the X series with the AMT driver & Waveguide can be a daunting decision.  What are your thoughts?  I was nervous selecting the X3s but now I have no buyer's remorse.  Every day I enjoy the sound better.

Marcus

Tyson

Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #1 on: 8 Nov 2021, 03:28 am »
Yes, this is probably the best tweeter in the world right now.  I did a lot of research before buying the X3's because I'd planned to DIY a 2 way speaker using whatever the best drivers I could find were.  The AMT tweeter was right up there with the very best, and I got to hear it in a few different designs.  I realized that I just really, really, really like the sound of horn loaded ribbon (or planar) tweeters. 

Once Spatial came out with the X3's, it also became clear that I couldn't really DIY something better than what Clayton had created.  So, order placed!  I'm very happy with my X3's.

abomwell

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #2 on: 8 Nov 2021, 07:21 am »
I think the crossover to the AMT is something like 1.5kHz if I remember correctly what Clayton told me.

Putting my ear up close to the tweeter sounds entirely different than with any dome tweeter I've experienced. I don't hear that high tinny sound with the AMT. In fact I really don't hear the tweeter at all but, of course, it's there and is VERY smooth.

Within the angular lateral range of the waveguide I've not experienced or measured much of a FR change by altering the toe in. I need to experiment more with that. The waveguide keeps high frequency spikes from piano and vibraphone to a minimum in my room which to me is a very big deal.

doggie

Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #3 on: 8 Nov 2021, 12:02 pm »
Good topic. This brings up a related design question that I have wondered about which is how each driver is crossed over.

I assume that the bass driver's Hypex amp has a built-in low pass crossover to keep it from trampling the midrange.

Does any one know how the tweeter and midrange are each crossed over? i.e. use a traditional network(LCR) or reply on "crossover-less" passive mechanical limiting?

Desertpilot

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #4 on: 8 Nov 2021, 12:48 pm »
Good topic. This brings up a related design question that I have wondered about which is how each driver is crossed over.

I assume that the bass driver's Hypex amp has a built-in low pass crossover to keep it from trampling the midrange.

Does any one know how the tweeter and midrange are each crossed over? i.e. use a traditional network(LCR) or reply on "crossover-less" passive mechanical limiting?

I am going from memory.  I believe the subwoofer is crossed over at 90 Hz.  It also employs DSP.  I believe the AMT driver is crossed over at 1,000 Hz.  Clayton does discuss crossovers in the interview.  If I understand him correctly, he does not use passive crossovers.

Desertpilot

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #5 on: 8 Nov 2021, 01:09 pm »
Adding to the discussion.  Traditionally, with dome tweeters, you want them at ear height and pointing towards your ears.  My seated ear height is 40 inches.  The center of my AMT driver is 47 inches (they are on Gaia II feet).  I have never felt the need to tilt the speaker forward to direct the AMT driver towards my ears (and I'm sure my speakers would fall over in this position).  Nor have I felt the need to raise my chair (wife would highly disapprove this anyway).  If I stand behind my chair, I have not detected any improvement.  I assume the wave guide helps.

Toe-in, however, is important.  For me, personally, I use a modest toe-in of about 15 degrees (AMT points several inches away from my ears).  If I point the driver towards my ears directly, I lose the speakers disappearing act.

mrotino332

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #6 on: 8 Nov 2021, 02:24 pm »
I'm fairly certain Clayton does not use any crossover from the mid to the tweeter and the mid just naturally rolls off at 1k or so where the tweeter is crossed over.  I had discussed on a phone call with him last year and that was my recollection.

Tyson

Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #7 on: 8 Nov 2021, 04:50 pm »
I'm fairly certain Clayton does not use any crossover from the mid to the tweeter and the mid just naturally rolls off at 1k or so where the tweeter is crossed over.  I had discussed on a phone call with him last year and that was my recollection.

That was true of the M series with the Sapphire tweeter, but I'm not sure it's true of the X series with the AMT tweeter. 

The bass woofer on the X3 does use an electronic crossover built into the Hypex amp I believe, to limit how high it plays.  In the interview, Clayton mentions he uses a 15uF Vcap ODAM in the crossover.  If he's using a 2nd order network, then that means the crossover point between the midrange driver and the AMT would be around 1khz.  That's VERY low, but crossing that low gives you a ton of advantages if your driver is robust enough to handle it.  The nice thing about the AMT is that it's developed for the pro sound market, so it is indeed very robust. 

The waveguide itself helps out here.  Most tweeters without a waveguide have a naturally gradual roll off as they get toward FS (their natural resonance point).  Often times you'd need some parts in the crossover to flatten this out.  But a waveguide (if designed well) can do that for you acoustically.  You not only get a flatter FR, you also get less distortion where it counts, near the crossover frequency. 

Fbczar

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #8 on: 12 Nov 2021, 11:24 pm »
Now that many of our members who regularly post have one of the X series models, I thought a thread dedicated to discussing the AMT & Waveguide driver would be helpful.

My understanding:
--Clayton says that this particular AMT driver is one of the best available (he hinted that there are lots of cheap "knockoffs" out there).
--My understanding is that he crosses over the driver at 1,000 Hz.  I'm sure there is a roll off involved to the mid-range driver.
--He employs the waveguide for "controlled directivity".

My research:
--A felt strip is used behind the driver to preserve the open baffle concept.  It is critical because mid and low frequencies will come into the rear of the driver causing chaos.  Some designers use a hard shell cap instead.
--The AMT design (moving similarly to an accordion) moves 4 times as much air as a dome tweeter.

My experience with my X3s:
--The AMT driver reproduces sound, in my opinion, much more realistically than a dome tweeter.  Especially horns, violins and female vocals.
--Clayton's design blends the AMT beautifully with the mid-range driver.  In other words, male (mid-range) and female (AMT) vocals sound natural and fully balanced.  No noticeable shift between drivers.
--The AMT is a complex mechanical structure.  Break-in is essential.  The more hours I get on my speakers, the better the AMT driver sounds.
--Brightness can be controlled through both break-in and shifting toe-in.  In fact, changing toe-in an inch at a time will produce noticeable results.

Choosing between the M series with a dome tweeter and the X series with the AMT driver & Waveguide can be a daunting decision.  What are your thoughts?  I was nervous selecting the X3s but now I have no buyer's remorse.  Every day I enjoy the sound better.

Marcus

The power handling of the X series is also important for those who use them in a home theater setting.

Desertpilot

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Re: Conversation Starter - X Series AMT & Waveguide Driver
« Reply #9 on: 13 Nov 2021, 01:12 am »
The power handling of the X series is also important for those who use them in a home theater setting.

Correct.  I do use them for home theater as well as music.  I can tell you, without a doubt, the X3s can handle movies right up to car crashes and bomb blasts.  An important note:  Getting the X series to volume match your other speakers can be challenge.  My X3s, of course are 97dB efficient.  But, my other speakers are 87dB.  Using Audyssey is almost worthless (it can't handle full range and highly efficient speakers).  I ended up playing pink noise and using an SPL meter to level match.  Plus a trusty tape measure for speaker distance.  This is for home theater applications only!  For music, I use a separate DAC going direct to my amp.  No Audyssey involved.

Marcus