Had a great time talking shop with Don Higgins of Periodic Headphones:
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The have the same IEMs made out of different material and a quick switch fixturey the have built themselves. Made for great science experience, pun intended

, on different driver material. They also have ultra small headphone amplifier with built-in battery that sounded really good. They gave me one to review. I was pleased that they had verified its performance using Audio Precision analyzer!
Their $99 IEMs are all built in Ventura County (California) and sounded pretty good!