DIY AMT: which of the three replacement diaphragms to use?

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Having seen that diaphraghms are once again available, I am thinking about taking up an old project of designing my own AMT. The motor will likely be similar to the sandwich design of most modern AMTs, i.e. a steel plate front and back with Neo magnets on the long sides. I was going to try and get a pretty open structure and optimize the radiation pattern with felt similar to the Neo3-PDR.

By printing the pictures from PE, I was able to derive the size of each membrane together with its radiating area. The f_s data were pulled from Strassacker.

part number 689-1107 689-1108 689-1109
width 30.16 44.45 31.75 mm
rad. width 21.54 24.81 20.89
height 141.29 119.06 74.61 mm
rad. height 112.79 93.53 55.53
pleads 13 17 17
f_s 550 ? 1400
according to Strassacker

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Sorry for the format, the board seems to eat all tabs and spaces.

#1107 is the replacement for the great AMT or AMT-1

#1108 is for speakers like the AMT-4 and AMT-6. The AMT-4 had a tweeter that looked like a slighty smaller version of the great Heil, i.e. same X profile. There seem to be two incarnations, one with the same very thin transformer sheet metal pole pieces and one where the individual sheets seem to be about 3 mm thick and actually have a slightly more complex shape. The AMT-6 uses 6 tweeters that are essentially the ferrite magnet version of today's common sandwich design, except that the two huge ferrite magnets were folded forward by 45°.

The #1109 is for the AMT-2 or Baby Heil, essentially a ferrite version of the Elac or Eton AMT.

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The big surprise was that both the 1108 and 1109 have 17 pleats as opposed to 13 on the original 1107.

If driver size, vertical directionality and NIB magnet cost are of no concern, the 1108 might actually be a better choice for a DIY project than the 1107, because
- it has more pleats limiting the displacement of each pleat (assuming equal depth, which is in fact unknown)
- it has roughly the same radiating area
- the plastic frame looks more solid

The 1109 lends itself for projects where size or cost or directionality (which might be better addressed by damping) are a concern.

Do you agree with the surprising result that the original design might not be the best choice?

[ThomasW]

email your question to Ricky at ESS, he has all the information regarding the Great Heil

ESS Laboratories USA