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Heil Air motion transformer for Cornwalls


jwgorman

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On 12/10/2018 at 8:33 AM, Chris A said:

Actually, you should get an increased backwave reflection from the corners since they form a (squashed) tetrahedral horn vs. the gain from a flat back wall. And since Khorns are typically placed in corners symmetrically, i.e., 45 degrees from each wall or false corner, you will get a fairly nice backwave reflection from the AMT and perhaps a little more diffusion from the tetrahedral surfaces that should increase the sense of depth of the resulting images. 

 

In any case, it's certainly worth a try on the Khorns.  Except for the three or so PEQs that I showed above (and reproduced again below) if you cross below 2 kHz, all you need to do is match SPL of the AMT with the midrange using a hand-held SPL meter. Note that I haven't had a lot of run-in time on the AMTs, so I reserve the right to update the PEQs below based on simply using them for a little while.

 

 

 

Chris

I ordered 4 of the big AMTs the other day :0) hopefully they wont' be back-ordered.  Picking up a 33 year old pair of Cornwall "1.5s" tonight on a local CL sale.  It will be fun to experiment with 

  • Cornwall stock surrounds
  • Cornwall AMT surrounds
  • Cornwall Stock center channel between K402 blends in living room and basement
  • Cornwall AMT center channel

Would the AMTs be worthwhile trying on top of the K402s perhaps augmenting the TADs or BMS full range or rolling them off and running the AMTs in the highest octaves?

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The problem with using any tweeters crossed above ~2 kHz is that the time misalignment starts to become extremely audible and sensitive to small changes in relative distance.  For instance, if you dial them in for sitting in chairs, suddenly, they're out of alignment if you stand, etc.  Additionally, the vertical distance between the horn axis centerline of the K-402 and that of the tweeter is usually several wavelengths, so polar lobing becomes a really audible issue.  This is why it's sooo much better to have a dual-diaphragm compression driver (like the BMS 4592ND) to go three-way instead. (The TADs don't need anything.)

 

As I type this, I'm watching Mahler's 1st with Claudio Abbado/Lucerne Festival Orchestra at concert volume (Blu-Ray 5.1).  I'm really impressed by the increase in the lateral sparkle of the surrounding sound stage due to the AMTs.  It's an immersive experience.

 

Chris

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lol, I opened my email when I got home from work tonight, and ESS says they shipped today via UPS, but the 32 lb notation makes me wonder... I just ordered one AMT... nevertheless, it's not a race for me... more like a work of art... also have a 1526C inbound also... picking up some 1/2" Birch sheets of plywood (24" x 30") at Rockler for 50% off, on Thursday and plan to glue-clamp together and trim up by Sunday... surfing for an xlica 2040 and an icePower amp for "research"... and now, a 58 something uf capacitor..... my calendar is looking like sometime in February

 

A couple of article's I'm missing to comprehend are:

  1. why does ESS call this speaker a transformer ?
  2. what kind of screw's hold the AMT to it's platform base... all the picture's I see, show two hole's through the top, but is this for a nylon tie, and something that wouldn't conflict with the thin diaphragms... regarding torque pressure or magnetics...
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Some great reading here guys thank you. I too have just ordered some ESS HAMT (great one) and will want to passively mate in a two-way with my Crites 15" woofer box I have made

(currently used in a 3 way with Altec 291 and Crites DE120 with my own crossover network that sings with this eclectic mix of drivers). I read that the ESS works better in a second order config. So I was thinking that for the woofer use 1.6mH (1st order) and for the ESS: 24.88uF and 1.6mH (2nd). I would obviously need to skirt around these values to fine tune and am also able to move the ESS around on top of the woofer box for better alignment. My room also has significant treatment that can be moved around taming nodal interference. My wife of course never enters the room!

 

Your thoughts would be much appreciated

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Remember that you'll have to reduce the sensitivity of your bass bin relative to the AMT by a few dB over and above the 1st order filter crossover values posted here.  How you do that is of course your call.  If you don't have any other way to check the levels, I'd recommend at least using a hand-held SPL meter in close proximity while playing pink noise in order to dial-it in. 

 

Since I'm bi-amping by Cornwall bass bin/AMT-1 arrangement, I simply use the gain control on the bass bin amplifier to attenuate down to flat response (using REW and a mike at 1 m).  I haven't calibrated the ICEPower (AMT-1) amplifier relative to the Crown D-75A (Cornwall bass bin) amplifier so I can't immediately tell you what that difference is in dB. If you find out what that measured difference is, it would be nice to know.

 

Note that the dipole nature of the AMTs relative to the bass bin will probably affect how you "voice" the AMT's level since the returning backwave is difficult to measure its psychoacoustic contribution to subjective loudness.  I find that this is also a function of standoff distance from the nearest room wall(s).  I do recommend a some absorption behind the AMT to attenuate the backwave if you find that you're placing it well within a metre/yard of said wall(s).

 

Chris

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2 hours ago, Chris A said:

Remember that you'll have to reduce the sensitivity of your bass bin relative to the AMT by a few dB over and above the 1st order filter crossover values posted here.

 

The AMT is rated at 96 db, so I will first try them with a pair of Heresy IIs, which should be a close match-up. Later, with my more efficient speakers, I could use some high watt L-pads for the woofers, or by going passive bi-amp and using an amp with gain control on the woofers. I also have a spare digital active crossover, but I want to try the passive systems first.

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Thanks for the tips Claude and I agree, voicing the integration will take time and I have a number of approaches including bi-amping, autoformers, l-pads but I like playing in this space, keeps me off the street. However I would have thought that the rating of the AMT is pretty close to the Cornwall bass bin and that my hearing would not notice much of a difference. I would think that the psychoacoustic interplay will take up more of my time. 

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Anyone that doesn't believe in drivers breaking themselves in within the first few hours of operation, here is a comparison of the step response of the AMT-1 plus Cornwall combination new out-of-the-box with 1.5 ms delay on AMT-1 (green trace) and after perhaps 12-24 hours of operation, no delay on the AMT-1 (red trace):

1039813272_AMT-1plusCornwallnewandbrokeninstepresponse.thumb.jpg.1b02c97fe88cf1ed3854fc13fbdb6506.jpg

 

 

That's about as much difference in response as I have ever measured from one driver (look at the negative going initial pulse near time 0).  Bottom line: get a few hours on your AMTs then recheck them to rebalance their DSP settings.  They apparently went from 1.5 ms delay (relative to the Cornwall bass bin) to zero delay.  The required EQ changed fairly extensively, too.

 

Chris

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4 hours ago, Chris A said:

Anyone that doesn't believe in drivers breaking themselves in within the first few hours of operation, here is a comparison of the step response of the AMT-1 plus Cornwall combination new out-of-the-box (green trace) and after perhaps 12-24 hours of operation (red trace):

 

883555950_AMT-1plusCornwallnewandbrokeninstepresponse.thumb.jpg.554deb47bedfaae9e176d960484c4428.jpg

 

That's about as much difference in response as I have ever measured from one driver.  Bottom line: get a few hours on your AMTs then recheck them to rebalance their DSP settings.  They apparently went from 1.5 ms delay (relative to the Cornwall bass bin) to zero delay.  The required EQ changed fairly extensively, too.

 

Chris

Good to know. That explains a lot. Thanks Chris. 

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,,, o O (Happy Hour kick's back in at 9pm) so I want to convey a thought that transpired earlier today, being the subject of a "Cornwall".... I was planning on building a cabinet... then I was planning on getting a used Cornwall... then I figured I could not "mess" with $1500 of a fine cabinet with Historical detail's.... and I found an old empty Stephens Speaker Cabinet on CL (maybe 1958 - san's all the components) so I actually made burn-off mark's in my old truck, on the street, getting to an atm and to an old storage building within 30 minute's of this revelation... $50 exchanged hands... but Khornukopia is still going to beat me getting his AMT wired up first lol cause I have to go back to work tomorrow....

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