When I played the Yamaha Baritone for the first time, I also had the feeling that nothing works in high range. Above C concert it became exhausting. I actually expected the baritone to be a specialist in high notes. Anyone coming from the euphinium must first familiarize themselves with the changed air flow and resistance. After playing the baritone almost exclusively in the last few months, lo and behold: Suddenly the high notes on the euphonium seem more arduous than usual. When I play both instruments every day, the range is exactly the same for me (highest usable note is F, fingering 13). So far, I haven't given any thought to the felts on my Yamaha instruments. But I'll have the instrument maker check it out.
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Sterling Virtuoso / Giddings Kadja
Yamaha 642 II / Giddings Kadja
Yamaha YBH 831S / Giddings Kadja S
Yamaha Flügelhorn 631GS / DW2FL