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 Post subject: AMT Heil Air (large)
PostPosted: June 20th, 2021, 9:02 am 
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I have what I think successfully integrated (electrically) the AMT Heil Air Transformer to the Razz replacing the original horn tweeter that is mounted on the front baffle with its diaphragm a full eight inches ahead of the mid horn. The original tweeter is disconnected.
First the AMT is just a wonderful tweeter if used properly and not trying to extend the low crossover point.
I an using the stock crossover sans the padding resistors to match the levels.
Not that the original tweeter was bad in any sense. It never called attention to itself which is a deal breaker for me. But improvement I am hearing are very gratifying. It might be the better time alignment or just the fact it’s a much better tweeter.
Right now the AMT is sitting up on 1/2 inch blocks and back a good eight inches from the front in line with the mid horn’s compression driver.
I have a piece of felt under the tweeter to help with reflections from the top of the baffle.
So I am thinking of building an enclosure for the AMT..
Just wondering if there is an advantage to extend wave guide out all the way to the front of the baffle.


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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 10:38 am 
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here is a pic

Attachment:
AMTRAZZ.jpg
AMTRAZZ.jpg [ 548.94 KiB | Viewed 1401 times ]


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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 11:25 am 
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Pelliott321 wrote:
I have what I think successfully integrated (electrically) the AMT Heil Air Transformer to the Razz replacing the original horn tweeter that is mounted on the front baffle with its diaphragm a full eight inches ahead of the mid horn. The original tweeter is disconnected.
But improvements I am hearing are very gratifying. It might be the better time alignment or just the fact it’s a much better tweeter.

I would expect both. The stock tweeter is not time-aligned by any stretch of the imagination and the AMT is a dipole without cavity resonance problems.

Just wondering if there is an advantage to extend wave guide out all the way to the front of the baffle.

That would increase efficiency and give you an opportunity to lower the crossover point (bigger "horn") to give the AMT more responsibility.

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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 11:54 am 
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I would expect, perhaps incorrectly, that the speaker manufacturer designed the crossover to compensate for the difference in the location of the diaphragm centers. Do you have an oscilloscope? It's easy to create chirps in Audacity so you can measure the true time alignment. I ended up using 3.5 cycle chirps to help verify phase. You may be surprised at the difference in appearance coming out of the speakers.

I used a dual trace scope, mine is digital which helps. I triggered on the output of the DAC and measured the delay in the time the signal came out of the midrange, then the tweeter with a microphone. You keep the microphone the same distance from the speaker cabinet. I focused primarily on the crossover frequency since I'm using Linkwitz-Riley crossovers which should maintain phase match through the crossover region. I set Foobar to repeat track so I get a chirp a second. It worked quite well. It may be tough to do without a digital scope with measurement capabilities. Although you can also have both drivers on and move the tweeter back and forth until the waveform on the scope looks as close to the original as you can get.

I tried to attach a chirp file but .wav and .flac files are not allowed. Shoot me an email and I'll be happy to send you one, or two.

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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 12:13 pm 
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DaveR wrote:
I would expect, perhaps incorrectly, that the speaker manufacturer designed the crossover to compensate for the difference in the location of the diaphragm centers.

In an ideal world -- maybe. As I recall from discussions with Paul -- it was only a second order crossover. That corrects somewhat for driver phasing -- but definitely not for time alignment.

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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 1:40 pm 
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The crossover has no alignment components from what I see. Just a straightforward 2nd order on hipass


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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 1:45 pm 
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I do not think I want to lower the AMT,s xover point. The highs sound very pure as it is.
If I change the tweeter xover then I would have to change the mid xover.
Right now I can put the Razz back to stock by just add back in the pad resistors.
In case I want to dump them


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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 3:13 pm 
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I agree with not lowering the crossover point. The Heil AMT you are using has many advantages but linear volume displacement is not one of them. BTW, the original AMT did have a cavity resonance because the top and bottom plates went straight across and did not have the V shape yours does. However the way it is mounted on the top of the speaker creates a cavity on the bottom half. On the original ones I filled that space with wool based carpet underlayment to reduce the resonance. You may want to rest the AMT on a layer of that material.

Tom


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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 3:19 pm 
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tomp wrote:
I agree with not lowering the crossover point. The Heil AMT you are using has many advantages but linear volume displacement is not one of them. BTW, the original AMT did have a cavity resonance because the top and bottom plates went straight across and did not have the V shape yours does. However the way it is mounted on the top of the speaker creates a cavity on the bottom half. On the original ones I filled that space with wool based carpet underlayment to reduce the resonance. You may want to rest the AMT on a layer of that material.

Tom

Look again. Paul mounted it on "stilts." The bottom open area is open on all four dimensions. At worst case he may have parallel reflective surfaces under the AMT, but I doubt that could even discerned when playing music.

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 Post subject: Re: AMT Heil Air (large)
PostPosted: June 20th, 2021, 5:20 pm 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
I thought I heard a difference when I placed the AMT on blocks with a piece of felt underneath. So thanks for verifying that possibility.
I knew the top of the box in front of the AMT would be a problem. I am thinking a turned teardrop cut in half and placed in front of the tweeter with flat side against the box


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