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Heil Air motion transformer for Cornwalls


jwgorman

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Yep that’s them!  I’ve even had good luck just sticking a 8uf cap on the amts and disconnecting the stock tweets. 

It is simply amazing how much just replacing the stock tweeters with high quality tweeters totally transforms these speakers (just using them from 6k up)

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On ‎12‎/‎6‎/‎2018 at 4:26 PM, ClaudeJ1 said:

Just think of how much easier it would be to do this to a Super Heresy (3.0???)

 

I disconnected the wires to the Heresy tweeter and squawker and taped the ends, then jumper wired at the binding posts up to the 50 uF cap and the AMT. Sounds very pleasant so far.

 

P1020861.JPG.eb1fc8d721641817340cc5326e2a2fa2.JPG

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8 hours ago, Khornukopia said:

 

I disconnected the wires to the Heresy tweeter and squawker and taped the ends, then jumper wired at the binding posts up to the 50 uF cap and the AMT. Sounds very pleasant so far.

 

P1020861.JPG.eb1fc8d721641817340cc5326e2a2fa2.JPG

Looks like a good first prototype. Now port the box and put a good woofer in there!!

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They played music for a continuous 100+ hours while I was away from home, so they should be broken in. Moved the AMT tweeters and jumper wires from the Heresy IIs over onto the Cornwall IIs, which provide a better SPL level match. I like the clear, sparkling high frequency response. Have not measured or adjusted yet, just listening and enjoying.

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7 hours ago, Khornukopia said:

They played music for a continuous 100+ hours while I was away from home, so they should be broken in.

That's probably a good bet.

 

7 hours ago, Khornukopia said:

I like the clear, sparkling high frequency response.

I like the whole thing: the sparkles, and the impulse response (time aligned with the AMT-1 set back about 6 inches (15 cm), and the coverage improvement in-room over the stock Cornwall.

 

Chris

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1 hour ago, Chris A said:

That's probably a good bet.

 

I like the whole thing: the sparkles, and the impulse response (time aligned with the AMT-1 set back about 6 inches (15 cm), and the coverage improvement in-room over the stock Cornwall.

 

Chris

What...wait...Chris, you're time aligning with a physical set back?  What about REW? the Xilica?

😁

Seriously,  can't wait to play with these this weekend!  Wish there was some way to be breaking them in while I am at work but I'm sure I don't want to be running a full range signal though them much.

How about some plush rug on  top of the cornwall bottoms (now tops) to hide wear and damp reflections?

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23 hours ago, Delicious2 said:

What...wait...Chris, you're time aligning with a physical set back?  What about REW? the Xilica?

😁

 

That's what I did with the tweeters on my LaScalas as I was using passive crossovers. Incredible difference.

 

Bruce

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On 12/10/2018 at 1:00 PM, Chris A said:

Okay, so based on my latest measurements today:

 

1) The delay value for the AMT-1 channels is about zero (0), so a passive crossover can be used, but I'd recommend a first order.  I'm using 6 dB/octave highpass and lowpass crossover filters centered at 800 Hz break-point frequencies.  This is good for the passive crossover guys--a simple capacitor and inductor is all you need--no more crossover circuitry is needed, according to what I just measured.

 

1464933137_CornwallbassbinAMT-16dBperoctSPLandphaseon-axis.thumb.jpg.adceea9be0a38e3509f984a91aece98c.jpg

 

This of course includes quite a few PEQs to smooth the response to ±2.5 dB (using psychoacoustic smoothing, as shown above).

 

2) I was fairly surprised by the difference between the left channel and right channel measurements, so I'd say that you would probably need to EQ in your own room via your own measurements.  I can certainly post mine here, but I have to say that the variability will probably nullify much of the gain that you might hope for. The good thing is that the frequency response without EQ correction is probably in the ±5-6 dB range, with about ±3 dB of ultra-smoothed central tendency wander of the response.  This is okay, but I would prefer a flatter response.  YMMV.

 

3) If you're measuring the AMT-1s within about 2 feet of the reflective wall behind it, be prepared to see some interesting measurements.  I found that I couldn't use the same EQ on the left channel as the right--and that's really a first for me due to the fact that my listening room is pretty symmetric, except for the bay window on the left.  Apparently, this is enough to significantly affect the output of the AMT-1 as measured by the microphone at 1 m...significantly...

 

4) I'm at a loss to explain the shift in measurements from last week to today.  Part of this is that I took a bit more time today to lay down absorption blankets, etc. so I could get much better phase measurements, but the delay values that I measured last week are not the same today.  I'd put a few hours of listening on the AMT-1s before trying to dial them in.

 

Good luck. 

 

Chris

 

Getting ready to measure these tomorrow.  I'll be using the Xilica 4080 which has just enough inputs and outputs left to biamp these surround channels.  If it's not optimal to max out the Xilica, I  could employ a mini-dsp 2x4 HD.  Sounds like I should measure left and right separately at 1m with starting xover at 800Hz low pass 1st order for the Cornwall woofer and high pass 1st order 800Hz for the AMT.  Is this a good starting place to run an REW measurement sweep?

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This is the first time, in my 14 years on the Forum, that I read die-hard Klipsch guys adoring a non-horn technology. I recall the original AMTs in the 70s. I need replacements for my hurricane-destroyed Dahlquist DQ-10s, which were my study speakers. (The Corns are fine). I have 2 Great Heils on order and I am thinking of using them with the DQ-10 Phillips midranges with some 12 inch woofers I have on hand, crossing at 250 and 1 KHz. These will have a foot print of no more than 14 by 14, reaching a height of about 34-36 inches. The mid will be in a felt-covered open back (as Dahlquist used them) which creates a sort of transmission line.

 

The study won't be back together for a few months, alas so I have plenty time to plan.

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1 hour ago, Delicious2 said:

Sounds like I should measure left and right separately at 1m with starting xover at 800Hz low pass 1st order for the Cornwall woofer and high pass 1st order 800Hz for the AMT.  Is this a good starting place to run an REW measurement sweep?

That's what I'd do, then take a sweep of both the bass bin and AMT together to get the relative gains and the polarity right.

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1 hour ago, boom3 said:

This is the first time, in my 14 years on the Forum, that I read die-hard Klipsch guys adoring a non-horn technology.

 

The AMT is actually a horn-loaded electro-dynamic diaphragm, i.e., permanent magnets holding a steady magnetic field upon which the moving folded metallized diaphragm film is alternately repelled and attracted while wrapped around the flat but spaced non-metallic diaphragm guides.  The modulating electric current flows through the conductive foil diaphragm to enable diaphragm motion folded around each diaphragm guide.

 

666653949_fig3blog.jpg.f1b90f9dbe0cd8d5ae3482f8cd89e052.jpg

 

US3832499-4.png

 

1711887309_fig4blog.jpg.29c5dcaba2c1affc192cc2dfaa506f92.jpg

 

366277004_fig7blog.jpg.17430283825bb0cc8b43879d7c74068d.jpg

The metallized diaphragm's impedance coupling to the coupled air mass is transformed via the trough-type horn with an open top and bottom--except where the surface upon which the AMT rests forms a horn closure. The trough horn nominally forms a 90 degree horizontal polar pattern. 

 

So the AMT is actually horn loaded...just without the same sort of horn that Klipsch uses.  If that horn wasn't there, the sensitivity/efficiency of the driver would be much lower.

 

Chris

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Actually the AMTs are just as much horns as the K-400 series of midrange horns on Heritage loudspeakers (i.e., K-260, K-500, K-600, K-700) except as they perform below about 2.2--3 kHz, where the horns lose vertical pattern control and start to paint your floor and ceiling with excess acoustic energy.  The AMT has increasing vertical directivity below about 2 kHz, too, and relies on the length of the AMT diaphragm area to control its vertical directivity above that frequency--just like a ribbon driver does. The horizontal direction is controlled via the "waveguide" straight-sided horn. 

 

I need to do a polar coverage plot of the AMT-1, but that's going to be delayed until after the holidays, I'm afraid.  In the meantime, here's a polar directivity plot of a Beyma CP25 tweeter for reference, first in the "vertical" direction (spheres top and bottom):

 

1135817266_CP25verticalpolarspectrogram.thumb.JPG.ea0d1b3448ea880d2cf3a588433e96ae.JPG

 

and then "horizontally", with the horn spheres side by side:

1067070587_CP25horizontalpolarspectrogram.thumb.JPG.7d2fa70b47055e220410ca67be30bfb0.JPG

 

All this says that you need to crossover the CP25 above about 5 kHz in order to avoid the polar narrowing in the preferred axis (called "vertical" but is actually the horizontal direction with the horn spheres top and bottom).  Just like other HF horns, the directivity seems to widen or wander around a bit in the other direction.

 

Chris

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With a basic first order HP/LP set on the Xilica I'll break these in as mains for a while.  Initial impression?  They don't give as pleasing a rendition of Seiji Osawa and the BSO performing The Nutcracker in Boston's Symphony Hall as do the K402/TAD/Khorn blend, but, OTOH they don't sound bad even switching back and forth.  Checkout the backlit AMT.  Perhaps one reason they say "sound as clear as light"😎

Break In As Mains.jpg

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