Bach 12 vs Bach 15
The Bach 12 has a wider cup diameter.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 12
• Baritone / Euphonium
Cup diameter24.50 mm / 0.9646 in
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 15
• Baritone / Euphonium
Cup diameter24.40 mm / 0.9606 in
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
Cup Diameter
The Bach 12 has a cup diameter of 24.50 mm / 0.9646 in compared to 24.40 mm / 0.9606 in on the Bach 15 — a difference of 0.10 mm / 0.0039 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.