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jwgorman

Heil Air motion transformer for Cornwalls

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18 hours ago, Delicious2 said:

What are your other PEQs Chris?  I"d like to use your settings as a starting point for my tweaking.

1124368990_CornwallBassBinAMT-1PEQsettingsscreenshot.thumb.GIF.c74e2ab398fab9f09a20db183b97f4ca.GIF

 

Note that the first 2 PEQs are on the Cornwall bass bin channel, and the remaining 5 4 PEQs are on the AMT-1 channel (the 660 PEQ is not needed).

 

These are for my right Cornwall channel, and that box with the AMT-1 on top is up against the wall.  There's a doorway into the next room starting ~2 feet to the right of the Cornwall/AMT-1 (looking at the Cornwall).  The left side of the Cornwall/AMT-1 has a full wall rack of CDs/DVDs/BDs that's about 6.5 feet tall and 4 feet wide (6 inches deep).

 

[EDIT: That 660 Hz attenuating PEQ is not needed--that was an artifact of the normalization process.]

 

Chris

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Well my AMT-I's arrived and I have put some ends on the cables and hooked up to a refurbished upside down bass bin (sans sound dynamics 12" woofer) using Chris A's 1st Order cross but with 1.59mH for 8 ohm 12" woofer. Thanks Chris and others for some very informative posts. Will try the Corn bin at the weekend with the smaller 1.15 coil. I did try a 2nd order but I think a waste of time/money, the 1st order works fine.

 

My room is small 4m x 5m with a bus load of room treatments but still the AMT is finicky to get right. What currently works is about 2m from rear wall and 1m from the sides, slightly towed in. It sits on the woofer box about half way but it's amazing how the sound changes by putting it at the front or the very rear of the box (front to back of box is 30cm). very room sensitive. Reminds me of the Martin Logan Montis I had for a few years. Scary as it sounds, I think the AMT-1 with my woofer competes well against the Montis and I would say the AMT combo is certainly more lively! The woofer doesn't go as low as the Corn but it keeps up with the speed of the AMT.

 

I also found that AMT-1 snaps into life when the purple wire is used as the +. It may be that the woofer is wired wrong but when I use the blue wire (from AMT-1) the sound becomes dull.

 

Anyhow stay tuned

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I got fooled by the normalized polar plot on the 660 Hz PEQ.  In order to give everyone a little better understanding of the polar performance of the AMT-1 + Cornwall bass bin performance, here is an un-normalized polar plot of the same data, showing the relatively consistent polars in a very noisy off-axis environment.  Note that part of that off-axis noise is due to the dipole nature of the AMT-1 re-radiating off the wall behind the unit and coming out at wide polar angles (i.e., above the 800 Hz crossover point):

 

10623115_CornwallAMT-1polarplot(2D).thumb.jpg.499c39eacf7206ac9cd9da7d218d0323.jpg

 

Note the two semi-circular areas of higher SPL off-axis, one centered at 500 Hz and the other at 800 Hz.  This is again a testimonial of the dipole nature of the AMT-1, in closer proximity to the partially reflective rear wall.

 

Chris

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Chris thanks again for the test results. Your first directivity plot looks like a Chinese Mandarin in a big robe, with his hands tucked into his sleeves. The second, if turned 90 degrees counter-clockwise looks like the robot from Lost in Space.

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Added the AMT to the Corn box (Crites 15" woofer) with about 3 db of attenuation and it sings. The AMT is beginning to relax and find itself. Certainly a great tweak for the Cornwall, you simply don't need a mid and a tweet when you have the AMT, it is very much a 'horn'!

 

all the best

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So in summary, a picture of the PEQs I'm currently using on the mid-wall located AMT-1/Cornwall bass bin is posted below.  The first two PEQs are on the bass bin output channel, and the last four are on the AMT-1 output channel.  The 176 Hz PEQ compensates the apparent 1/4 wavelength cancellation to the wall behind the woofer.  If your loudspeaker is spaced farther from the wall, this cancellation will occur at a lower frequency:

 

598197913_CornwallBassBinAMT-1PEQsettingsfinalscreenshot.thumb.JPG.b56865533e6a44d651993b8bcf9df461.JPG

 

Chris

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27 minutes ago, Chris A said:

If ...

question... are the crossovers hooked up inside your CW … (to make the 600 to 800 cross)... I think I remember reading that the woofer was only connected directly to ur amp?

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I'm using an ElectroVoice Dx38 (DSP) crossover connected to two stereo amplifiers--a Crown D-75A for powering the woofer channels, and a ICEpower 50w amplifier for the AMT-1s-- whose outputs are directly connected to the woofer (one channel for each woofer) and AMT-1 (one channel for each AMT-1).  That's how I'm able to EQ the loudspeakers to flat response, the parametric EQ filters of which are shown above.

 

If you were going to use passive crossovers and mono-amplify each, you could use only an inductor in series on the Cornwall woofer, and a capacitor on the AMT-1 channel, whose values each are shown below.  Then you could use upstream parametric EQ somewhere in the signal chain to re-EQ each loudspeaker using values similar to the values shown in the above. 

 

XSim screen shot 1.JPG

 

Chris

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Posted (edited)

... o O (a 50uf cap get's within 10%) ... but is there a 56.2uf cap for a passive to be found anywhere other than using 2 or more in series ?

Edited by windashine
... cowboys won

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A 50 in parallel with a 6.2. Parts Express is your best source for these incremental values 

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15 hours ago, windashine said:

... o O (a 50uf cap get's within 10%) ... but is there a 56.2uf cap for a passive to be found anywhere other than using 2 or more in series ?

Using capacitors is series increases the Voltage rating and the ESR. Using them in PARALLEL is what increases the capacitance value. Boom3 is right.

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For the single seat hot rod effect to see how good it can get I set the couch off to the left and pulled the single stuffed chair out away from the window.  Listening is only with the heavy MoonDream brand drapes closed.  With Chris' settings minus the 176Hz bump and the front channels mixed together a bit for better center fill it's starting to sound very good.  Of course, it doesn't hurt that I'm discovering excellent new (to me) surround mixes such as Riverside's Love, Fear and the Time Machine and Steven Wilson's sampling of the first 3 Gentle Giant albums - Three Piece Suite.

Single Seat Away from Window 2.jpg

Single Seat Away from Window 3.jpg

Single Seat Away from Window 4.jpg

Single Seat Away from Window.jpg

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On ‎1‎/‎5‎/‎2019 at 11:54 PM, windashine said:

... o O (a 50uf cap get's within 10%) ... but is there a 56.2uf cap for a passive to be found anywhere other than using 2 or more in series ?

 

Parts Express has a 56 uf cap. 

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I cut 3 sheets of 30x60, 9 ply bb yesterday for one speaker cabinet using a kreg track saw device and a 60 tooth new saw blade, to the dimensions for a CW1... I can't believe how square everything came out... like I was expecting the outside of the cabinet to resemble a trunk on a tree when I was finished...  I went with this speaker to assist in the tuning, (and jwgorman's thread) which leaves me with an older Stephens speaker cabinet completely disassembled and off into the corner, out of the way....

 

The cabinet port location on the motorboard is so far following the inverted design (upsidedown) and left me wondering if it should be in the middle, or split in half on the side's, or use round plastic ports, among a few idea's... except for to the back, or on the bottom... I expect to follow Chris A's recommendation to keep it near to the AMT1 - but won't be routing the mid horn or tweeter cutouts, which relays into my next search to add a brick or extra cabinet bracing to maintain the enclosure volume... and more part's are ordered... Thank you too Khornukopia, as I was just logging on yesterday, and saw your PE idea... all in all, for the price, I'm game... whereas in the past, I had an idea about 5 jupiters !

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24 minutes ago, windashine said:

cabinet port location on the motorboard is so far following the inverted design (upsidedown) and left me wondering if it should be in the middle, or split in half on the side's, or use round plastic ports, among a few idea's... except for to the back, or on the bottom... I expect to follow Chris A's recommendation to keep it near to the AMT1 - but won't be routing the mid horn or tweeter cutouts, which relays into my next search to add a brick or extra cabinet bracing to maintain the enclosure volume..

Since this is custom for the AMT, keep the woofer as close to the top as possible and put the port near the floor, facing forward. The port produces only frequencies below 100 hz. so having it that far from the woofer is not a problem. It's actually better because you will have a floor mirror reflection of the low bass from the port which enhances it. Also, don't bother with the Bricks, only bracing, and don't worry about the extra volume from lack of midrange and tweeter horns inside, it works in your favor.

Untitled.png

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UPDATE

I have been fooling around with various xover networks and have found, to my ears at least, that a 2nd order Bessel with a Zobel across the woofer works best, if fact it opens up the AMT and helps it blend better with the woofer (Crites woofer). Still you may need to move the AMT around the top of the Corn box to get the best alignment for you room. It is an amazing combination

 

all the best

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