Well, the volume of air between the nozzle exit and my drums isn't exact. I'm not suggesting this is the IEMs fault, but I can hear different resonant peaks between 6k and 7.5k. As I use a controllable sine sweep I can hear the resonant peak first in the left, then right, then left again, then right a last time. They're very close together, but not spot on. But to be honest , they're not very big peaks at all, perhaps 3db at most according to my attempt at EQing for equal loudness. Honestly, I was afraid that the peaks would be pretty extreme, but as Piotr told me in email, nothing troubling would happen. I'm happy! The fit is just right and didn't take long to adjust to at all. I might also add that they respond to EQ just fine. That was another concern of mine, that the single driver wouldn't be able to hang with EQ change. But, keep in mind I'm only correcting 3 db here and there with pretty sharp Q values. oh man, you're a better designer than I am. yours look outstanding!