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Have you tried with foam tips?
I honestly think he is having a seal problem which will make the highs messed up
I agree. When I first got them I had the same issue until I tried several different foam tips.
I've only rolled the tips that came with them. Are they no good?
I couldn't get a good seal with any of the ones that came with them. I found a foam tip from something else I had on hand and that did the trick. I'm sorry but can't remember what they came with. I suggest trying other tips until you can get a deep insertion with a good seal.
I feel you. Sadly, none of the stock tips worked for me either. Get these Ostry tips shown below, they should be easy to source from Aliexpress or Amazon (in case you can't find them anywhere, PM me and I'll send you some).
The comply ts 400 are best I use medium
I would first off, let your duke run at a medium to low listening level for over 200 hours before critical listening. Micro drivers really need proper burn in, longer than dynamic drivers like in the Zen, which I believe still need over 100 hours. After that play John Mayall "jazz blues fusion, live in Boston". I hear zero sibilance using chord mojo and a decent source 80 percent of the time. Yes you will get the occasional harsh recording, but the Dukes were built to be "Brutally honest". I would give your microdrivers a proper burn in.
With due respect - there is no evidence to suggest (other than anecdotal / subjective - which isn't evidence) that micro drivers, dynamic drivers, or BA drivers change at all from burn-in, and definitely none that suggests major changes.
Claiming it as fact is dis-ingenious at the very least.
I've measured plenty of earphones, BAs, hybrids, dynamics, micro--dynamics. Their frequency plots do not change. Shures engineers have already stated publicly that none of the earphones in their range (dynamic or BA) change - even after thousands of hours. Any change you think you've heard is merely your brain getting used to the sound (brain burn-in).
@laxtrax - we all have different frequencies which affect us as far as sibilance goes. My advice would be to try and get a deeper insertion, as this can physically alter the frequency plot (and its due to the narrowing and angles of your ear canal. This can sometimes help with sibilance. Otherwise move onto another earphone which does not hit your particular personal sibilance frequency range. Foam tips may be the other thing that could help.
Forget the physical burn-in though. It won't change a thing.
Any thoughts on why Duke measurements are the way they are? I suspect all the treble troubles (lol) can be identified somewhere in there.
The way they were tuned. That spike at 7 kHz (15 dB above 1 kHz) is the one you're finding sibilant. Many people won't - some people will. If the fixes I gave you don't work - then time to try something else. Everyone had a different sibilant frequency peak/threshold.
It's actually very spiky in a way I rarely see, and I'm curious what it means. The closest I know is this Ultrasone.
Agree to disagree on that. It's not night and day but the freq. extremes smooth out over proper burn in to my ears. No it's not something you can prove on paper, but depending on design some manufacturers do recommend it, if anything to protect the drivers. Never claimed it as a fact, but in my opinion it's worth giving gear the time to sound its best if the maufacture recommends it.
In that case I suggest you ask Lee directly. He's someone who I have immense respect for, cutting through a lot of the myth and audiophile BS many claim that they hear - yet are unwilling to prove (which can de done ridiculously easily) by measurement. Lee will tell you exactly what I have. Burn in will affect the Duke no more than any other of his earphones.
Manufacturers who claim it should be ashamed of themselves - or they should put up the measurements. These are not full sized speakers with a spider. We can (as you say) agree to disagree - but I would strongly suggest you conduct some experiments (properly controlled), measure the output, and then you might just change the way you're thinking.
How reliable are measurements when something like that Duke can sound good once you tame the sibilance (no success yet on my end, will find those foams) even though its FR is all over the place?