Yup I would agree on most of that.Haven't heard the Expanse yet but I feel like this interview with mixing engineer Christoph Stickel has a nice description of the differences:
What I heard is Stealth having more "energy" more clarity in 1k-3k region and Expanse focusing more on the ~5k and above. And I'm not sure if it's only because of slight frequency differences or something else.
I let myself to make bold assumption that it's because stealth is more "damped" through AMTS. When you look at the Stealths driver AMTS is covering whole driver while on the Expanse AMTS has more "holes" in it and you can see more of the driver itself.
Looking at the group delay of both you can see some small differences in the range between ~1k - ~8k
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I know, the differences are small (probably on the edge of measurement error) moreover it's unknown how actually it affects sound - how we perceive it.
But I'm thinking that it's because less reflections/interactions inside the cup (that we can see from the graphs) Stealth has more "precise" images less "blurring" sound.
When you examine group delays of IEMs you see even clearer graph as there is even less reflections as you insert them deep into your ear canal - that's what I hear with IEMs, very clear images, something that only Stealth comes close in that regard.
Anyway as I said everything that I wrote above is my bold statement\assumption.
Would be nice to hear something from @mrspeakers if he has something to say on that topic (I'm always extremely curious about technical stuff)
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