Inconsistent Heil AMT measurements

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Hi All, I have seen graphs on the great Heil AMTs that go out past 20khz and others that start dropping off at 10khz. Here are two examples I pulled off the web. What is your experience?
 

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There are 'great AMTS' of various vintages out there, and unspecified changes to the membrane material . Not to mention the normal variances in measurement conditions, gating, etc. And the manufacturer has made no real effort to resolve this, by sending samples of the current production to audioxpress/voicecoil or even any of the prominent DIY measurement sites. Thus it's very hard to compare them to other modern tweeters and HF transducers.

My impression is that ESS is happy to sell these based on reputation and audiophile nostalgia, which is likely a workable strategy, though one that means I'm unlikely to buy a pair anytime soon.
 
Great heils have had a lot of different diaphragm designs, as well as frame and magnet. They're generally similar in the same way that multiple seas tweeters have a lot of similarity. Some are more or less efficient, have different peaks etc.

There's a kapton version, an aluminum and polyethylene version (first), and other iterations in between. There's also the magnet- different plastic frames, different magnet setups (black coated steel v. raw, other design choices)
 
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