Replacement same model tweeters like a major component upgrade

1 - Usually the physical break-in is related to the suspension, and its worse for larger, traditional drivers. AMTs have no suspension to break in so there’s no history I’m aware of that those tweeters ever "break in" but certainly I’ve heard the capacitors in series break in.

2. I’m really surprised this happened, AMTs are incredibly reliable and consistent performers. More likely you are hearing a new model.

3. Drivers require a lot of careful analysis to properly integrate with other parts of the speaker. We often read in DIYaudio a story like "I have this 20 year old speaker my grandfather left me and I got these tweeters on e-bay, how do I put them together?" and often the answer is they are better of making a pre-built kit because the knowledge and measurement and care they will need to fit a random part into a speaker is too much for a first time attempt.

And oh, yeah, DIY speakers can be tremendous values. If you want to "upgrade" your fancy speakers, sell them and DIY a new kit. You’ll be better off in so many ways.  The only real benefit of this approach is how much you learn, but if you are modding a name-brand speaker your learning experience will often be a lot cheaper with a new kit.

AMT tweeters are far more delicate and easily prone to injury. I've often womdered about the crittical tension required for proper operation. There would be no way of knowing if the tweeter is out of spec. The effects of humidity, hot to cold or any type of air disturbence isn't good and could knock them out of whack. An innocent  vacumm cleaner across the face of the speaker would instantly ruin these delicate tweeters. How would you know?

However, I love the sound!!

@tlcocks  Do you mind my asking the price you paid for both tweeters?

$154 each

Yes, Erik it seemed like it was a new model. I’ll have to ask ML

I also love the sound of this tweeter. It’s a wonderfully smooth and natural yet articulate high end. Great recordings cymbals sound amazing with this AMT

1. I’ve replaced the tweeter on just one side of Tannoy Kensington SE, years after their purchase. Almost certainly a different batch of manufacture, but same part number. No break-in required - the drop-in sounded perfect and continued to do so! Old tweeter still sounded great too; just developed a VERY slight resonant ringing noise (only noticeable one in a long while, on certain loud piano notes) that possibly could have been addressed by a careful cleaning. Wish I’d tried. Spares are hard to come by now, though Lockwood makes new replacements.
2. Varies wildly by driver type & implementation. Planar magnetics are very different than other types. At issue there, I guess would be the coil’s "printing" on its VERY thin and delicate membrane material. Bad news if that starts to separate. Electrostats also have a very thin & delicate membrane, but without the complications of a printed "coil" - mainly, keep them away from dust or anything that could poke them. Many dynamic coil tweeters (the most common kind) could last decades or more with NO degradation (e.g. Tannoy "pepperpot" tweeters, like in the Kensington). Other dynamic coils (like Tannoy "tulip" DC’s) used ferrofluid in the gap, which can dry out (after say 20+ years?) - in that case, the old crusty fluid should be cleaned out and replaced with new fluid of a similar viscosity. Its performance can be degraded until this is done, but there’s no reason its lifetime has to be limited by this.
   
   The biggest risk to most tweeters is physical absue. 

I had  a pair of speakers years ago with this type of tweeter.  I had buzzing issues which continued even after replacement of the pleated membrane.

I'm sure some of these sound great but agree these can be less robust than traditional designs.

I am researching and it’s unclear to me if what ML calls an ATF transducer is actually an ATM, the latter of which requires not only a magnetic field but also a pleated diaphragm. I cannot see whether my tweeter has that pleated diaphragm. Help?  I see several of you have called my tweeter an ATM. Is it?

Sorry mean AMT

So the tweeters continue to sound brighter in a good way and more detailed. Perhaps the old ones were damaged or voice coil delaminating or something. ML verified the model of these replacements is identical to the original.