Bach 4 vs Bach 6½A (small shank)
The Bach 4 has a wider cup diameter, the Bach 6½A (small shank) features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 4
• Baritone / Euphonium
Cup diameter26.00 mm / 1.0236 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 6½A (small shank)
• Baritone / Euphonium
Cup diameter25.40 mm / 1.0000 in
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
Cup Diameter
The Bach 4 has a cup diameter of 26.00 mm / 1.0236 in compared to 25.40 mm / 1.0000 in on the Bach 6½A (small shank) — a difference of 0.60 mm / 0.0236 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.