Heil Air motion transformer for Cornwalls

[Chris A]

29 minutes ago, pzannucci said:

Am I reading that correctly?  You had to add 7db on the lower end of the heil but dropping the output around crossover of ~900?  Would inversing the polarity work to pick up some of the distance change?

 

I tried inverse polarity.  It resulted in a big suck-out at higher and lower frequencies from 800 Hz center crossover frequency. 

 

You don't have to use anything--it's entirely up to you.  In my setup, using my UMIK-1 calibrated microphone, Dx38, and amplifiers (an ICEpower for the AMT-1, and a Crown D75A for the Cornwall bass bin), using the microphone position and time gating that I used, this was the answer.  YMMV. I provided the information to you for information only.  The reason why I posted the plots above was to show its performance so that I wouldn't get second-guessing of my qualitative statements.  You be the judge.

 

Note that the stock Jubilee/two-way uses more PEQs than this and of larger overall gains (top to bottom).  This is really quite mild since there are no further PEQs on the AMT-1 that I'm currently using.  That's pretty spectacular, IME.

 

Chris

[pzannucci]

The info is much appreciated.  Thank you.

[Chris A]

A plot of the ESS AMT-1 electrical input impedance magnitude and phase vs. frequency.  (This isn't very exciting, but here it is):

 

 

[Delicious2]

On 12/6/2018 at 1:19 PM, Chris A said:

 

I'm listening to these surround Cornwall/AMTs right now playing a 5.1 Yellowjackets New Morning Blu-Ray.  It's pretty spectacular.  It's also possible to move the AMT-1 around to put the HF energy where you want it in-room. As surround loudspeakers in a 5.1--this is something that I've wanted for a long time.

 

Chris

So I'll be looking for compatible surround speakers for both my living room setup with K402/TAD/Khorn L+R and the HT setup with K402/BMS4592ND/Peavey FH-1 L+R.  Should I be looking into used Cornwalls?  At least buying 2 pair of these tweeters while on sale?  I get that they need some room to breathe.  The only thing better would be...?...K402 MEH?

 

[Chris A]

The Cornwalls are direct radiating/horn-loaded hybrids but they do pretty well for a bass reflex box--in my experience.  Full-range wide coverage MEHs will probably have the best overall performance including cleanness of midrange/midbass due to woofer-horn loading (the K-402-MEH or DIY wide-coverage MEHs being the only economically viable choices among those).  The K-402-MEH is my plan in the longer run for my main setup. 

 

But Cornwall/AMTs are a good choice if you're only using the surrounds as surround echo channels for movies.  They usually run at much lower SPL and are not as susceptible to modulation distortion issues.  Just look at the lineup of Klipsch cinema surrounds.  You won't find any with horn-loaded bass, and most are sporting extreme wide coverage for commercial movie theaters, but that is not really required for HTs because of the tighter spacing of seats in the HT relative to commercial cinema:

 

[Chris A]

I wasn't expecting much difference in the sound of the setup (in 5.1 mode) from the 3-way Cornwall vs. the Cornwall/AMT-1s, but I have to say that I'm floored.  The AMT's provide so much more sparkle and lightness of sound that I have to say that the surround experience is finally one that I've been looking to have for a long time. Even at low loudness levels, the clarity and lightness of the AMT-1s add significant performance. 

 

Chris

[windashine]

1 hour ago, Chris A said:

but I have to say that I'm floored

 

… this is all it took for me this morning, to order a single ESS AMT-1 … o O ( I hope they don't backorder )

[jwgorman]

 

If I could paint, I’d grab a black velvet canvas and paint Oscar Heil and Paul Klipsch shaking hands in front of the stairway to audio heaven. 

[Chris A]

Just thinking...

 

A stereo pair of new Cornwall IIIs at $2199.99 each = $4399.98

 

vs.

 

Used pair of Cornwalls in good condition (about $1000-$1500) + a pair of AMT-1s ($280) + an miniDSP 2x4 HD ($205) + an extra amplifier like an ICEpower ($180) = $1665--$2165

 

You could upgrade to a Xilica XP2040 (~$900) bringing the total to $2360-$2860. 

 

[I've got a set of miniDSP 2x4 HD EQ filters in a text file that you can use to import into the miniDSP or Xilica.]  If you buy Cornwalls, they will appreciate slowly over time to cover the depreciation on the AMT-1s, miniDSP 2x4 HD,  and ICEpower amplifier (especially if you recondition the wood cabinets on the Cornwalls...strangely enough), yielding a net-zero cost "listening trial".  If you've got a pair of Cornwalls in storage somewhere, this is a no-brainer upgrade, IMHO.

 

If you're into building boxes--a pair of K-33-like woofers (Crites 1526 cast frame) = $295, two pieces of veneered 3/4" 4'x8' plywood = $110). 

That brings the lowball price down to $1070 for the pair.

 

This puts the price/performance of the AMT-1s into perspective for me.

 

Chris

[jwgorman]

I like that analysis. 

[windashine]

7 hours ago, jwgorman said:

I like that analysis. 

 

my analysis curtails a single Crites Cast 1526, in a soon to be built 6 sided (or more) rigid dimensional enclosure... with the AMT-1 on top of the box... don't mean to change the topic so that's about it... besides figuring out the crossover and remaining employed for refreshment expenses during nice weather... the single build mono theory enable's my 1954 Klipschorn to chime into the non stereo aspects of my listening perspective...

[Chris A]

57 minutes ago, windashine said:

my analysis curtails a single Crites Cast 1526, in a soon to be built 6 sided (or more) rigid dimensional enclosure... with the AMT-1 on top of the box

If you're planning to cross over at 800 Hz to an AMT, I actually recommend one 15" woofer.  Two woofers would cause you to limit your crossover frequency to about half that frequency (400 Hz) in order to avoid polar lobing between the woofers, i.e., you're looking at a three-way loudspeaker if you use two or more K-33-type woofers.  As it is, you need to get the AMT itself as close to the woofer as you can to avoid excessive lobing of the woofer with the AMT in the crossover interference band.

 

JMTC.

 

Chris

[windashine]

figuring a modified Type B, with just a 2.5 mH Air Core to a single 1526C... san's the roadmap to the tweet for a 2 way project, then a ( ? uf) have a 6.8 on hand, capacitor and another air core inductor (?) to the AMT... but semi-interested in a La Scale type cabinet with one inch wall's, stretched to place a cast frame inside, that's another story... nevertheless... the cornscala type of cabinet with cornwall sound cutout's on the bottom (the 3 rectangles) further reduced in height, to eliminate the horn and hf tweet cutout's is also making it's presence under my palm leaf hat... to get the AMT closer to the woofer...  Thank you for the reply... I also enjoy Marshalls version of his $200 cornwall saga from 2009.

[profsbg]

Cost aside, how would the AMT-1 compare to using a K510 (and active crossover)? What is the downside compared with the latter horn loaded controlled-directivity approach?

[Chris A]

Well, if you ask me, my response would be the following:

 

1) I spent about 5 years total calendar time with tri-amped JuBelles having Belle bass bins, K-510 midrange horn/K-69-A 2" compression driver, and Beyma CP25 tweeter. [I eventually went to three-way from two-way because of the chattering of the K-69-A 2" compression driver, so I added a third amplification stage and the Beyma tweeter--albeit crossed at 8 kHz, and dialed in using REW.]  I can say that arrangement sounded completely neutral to the Jubilees/TAD 4002 drivers on either side.  The down side was the apparent source width of the acoustic image, which wasn't nearly as wide as the K-402s/TADs on either side.  That caused me to move on to the K-402-MEH design in order to get the same timbre/neutrality and apparent source width in order to seamlessly integrate a L, C, R array with the Jubilees (I can't fit a third Jubilee between the corner Jubs due to room restrictions.

 

The bottom line here is "apparent source width".  It's important to having a seamless front-of-room acoustic image.  From my reading of others with their experiences of narrower coverage horn-loaded loudspeakers (including Danley SH-50s/60s etc.) many people either don't have very large listening rooms (in fact, way too small), or they have been trained to listen with their "head in a vice"--a concept that is made totally obsolete with the K-402s.

 

2) I spent 20 years with dipole Magnepan MG-IIIa's and learned that their extremely low mass diaphragms sounded very transparent, but the limitations of their dipole nature and very large surface area causes issues with the wavefronts combining from across the height and width of the loudspeakers to be in phase, thus having a "head-in-a-vice" restriction (and you really cannot toe-in dipole loudspeakers without creating a huge "hole in the center" backwave pattern that is angled away from the listener in the center between the loudspeakers).  These loudspeakers have a ribbon tweeter that extends the full height of the loudspeaker on the inside edge closest to each other.  (A picture of those from ~25 years ago below--suitably decorated for the season and pushed back out of the way in their non-listening positions.  They need at least 6 feet from every wall surface to get their best sound.)

 

 

3) The ESS AMT-1s that I'm using have the transparency of the Magnepans, and the coverage of the K-510 horn with 2" compression driver.  This means that the restriction of the "head-in-a-vice" is not present in these drivers.  They also seem to be much more robust than the Magnepan ribbons (of which I sent back to Magnepan for repair several times over their service life due to the power required to get them to anything close to concert level).  That restriction is greatly relaxed in the AMT-1s which are much more electrically/acoustically efficient than the Magnepan ribbons (probably about 10+ dB or more sensitivity increase with the AMT). But they are still dipoles, and as such present a conundrum in terms of where to put them.  The back wave needs distance to the closest wall, while the bass bins need to be within 12 inches of the wall, or better yet, a corner, to increase and smooth their response as PWK designed them.  The Cornwall bass bins can be properly reinforced with a bass bin baffle extension (i.e., "false wall") to smooth out and extend the frequency response down low and overall smoothness of response, but that makes them significantly wider.  But this is easy to do.  [The K-510/2"compression driver in the JuBelle has no such restrictions, but then, it doesn't have quite the same reproduction lightness as the AMT-1 has.] 

 

4) The place where I use the AMT-1s is in the surround loudspeakers in a 5.1 array.  This means that I need the widest coverage pattern that I can get. The K-510/compression driver will do about the same as the AMT-1 in that role horizontally--so this is basically a wash in terms of K-510 horn vs. AMT-1. 

 

5) The AMT-1s cost $140(USD) each, while the K-510s/compression drivers cost ~5x that price in order to get a good enough 2" compression driver.  You can do the math. 

 

Chris

[Chris A]

By the way, it appears that the AMT-1 also has horizontal and vertical controlled directivity down to some frequency (horizontally probably 1500-2000 Hz based on the size of the "V" aperture, and about the same vertically).  I think a lot of people are missing this.  This is part of the story as to why the AMTs are so efficient--they're mounted on trough-type horns.  You could extend it further if it needs it by doing something like this:

 

 

I bet those sound really good, and this is entirely possible with a dual woofer approach.

 

Chris

[ClaudeJ1]

On 12/7/2018 at 11:17 AM, Khornukopia said:

Just trying to be funny. I have more speakers and parts than a normal person should own.

There's nothing "normal" about any of us....................silly boy! 

[ClaudeJ1]

On 12/7/2018 at 8:39 PM, windashine said:

 

… this is all it took for me this morning, to order a single ESS AMT-1 … o O ( I hope they don't backorder )

I have a couple of used ones I don't need if they run out. FYI.

[Khornukopia]

15 hours ago, ClaudeJ1 said:

There's nothing "normal" about any of us...

 

Yes, I have always considered my fellow forum members to be highly intelligent and very helpful.

[Khornukopia]

16 hours ago, Chris A said:

The back wave needs distance to the closest wall

 

Is there an ideal distance from the backside of the AMT to the wall surface behind it?