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Old 27th February 2009, 07:50 AM   #1
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Default Stacking Heil AMTs

Just wondering if anyone has tried stacking Heil AMTs?

They have a strong magnetic field and I'm wondering if that could cause issues between the drivers if they are stacked one on top of the other.

Came across this cool pic of a AMT-6 speaker.

They have the Heils mounted sideways in a horizontal array. Interesting!

Cheers

Lar
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Old 11th March 2009, 12:00 PM   #2
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Lar, there may well be a right and a wrong way to stack the Heils with reference to magnetic cancellations, but I don't think this will be as significant as acoustic considerations. Directivity is a function of acoustic size (the ka factor) ka=transducer dimension divided by wavelength (lamda). As frequency is part of the equation the directivity will vary with frequency.

Unlike a dome etc the Heil is acoustically small (fractional ka value) in the horizontal plane up to 20kHz, but in the vertical plane it becomes acoustically larger beyond 4kHz odd and has narrowing directivity. This is of a type where the extreme high frequency level tends to change between sitting down or standing up listening. By stacking Heils this is going to occur from lower frequencies and be more extreme.

In the photo of the horizontally arrayed Heils the vertical pattern will be quite broad, but I would have reservations about the horizontal pattern. It is likely to be rather "fingured" Sorry if I am telling you things you already knew, but acoustic knowledge is a very valuable asset in understanding loudspeakers. I actually own a pair of Heil tweeters and admire many of their attributes, but directivity is not one of them!

Keith
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Old 11th March 2009, 07:22 PM   #3
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Thanks for your response Keith!

Looking at the way the Heils are arrayed in the AMT-6s made me wonder about a similar set up where the two outside Heils are placed right side up and the inner two on their sides.

Would probably be cancellation issues though.

With di-pole cancellation as an issue I wonder about what some people have stated about improvements to the sound of the Heils made by dampening placed behind them.

Cheers

Larry
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Old 12th March 2009, 07:45 AM   #4
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Lar', My Heils are no longer in use as one of them needs a new diaphragm and I have the Linkwitz Orion dipole speakers. In the final use of the Heils I mounted them in enclosures in the belief that rear radiation was undesirable as it was going to reflect off the wall behind and comb filter with the front radiation. After reading up on acoustics and psycho acoustics I now realise I was mistaken in this belief, as what happens with binaural hearing is completely different to a microphone receiving sound from two sources such as a direct sound and a reflected version.

I think the decision monopole or dipole needs to be made in the context of the entire system design. If the only rear radiation in the system is from the tweeter the diffuse (reverberant) energy in the room is going to be rather "tizzy" (top heavy). Dipole cancellation and how they may behave with dampening behind them are two different subjects. Do you mean dampening on the wall behind the Heils or enclosing them in a box with damping materials added? When we enclose the rear we no longer have dipole operation and hence no dipole loss. www.linkwitzlab.com/ is a good read on dipoles.

In general, where tweeters are concerned "small is beautiful"

Keith
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Old 12th March 2009, 08:24 AM   #5
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I've done a bit of research on the Linkwitz dipole; interesting stuff! The crossover design is fairly complex. Did you ever consider pairing a Linkwitz dipole with a Heil?

Lar
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Old 12th March 2009, 04:50 PM   #6
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Did you ever consider pairing a Linkwitz dipole with a Heil?
It has occurred to me; there would be no need for the rear tweeter and the Heil should cope with the low crossover frequency quite happily. I still prefer the broader directivity of the domes.

Keith
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