Bach 15D vs Bach 18
The Bach 15D has a wider cup diameter, the Bach 18 features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 15D
• Baritone / Euphonium
Cup diameter24.40 mm / 0.9606 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 18
• Baritone / Euphonium
Cup diameter24.20 mm / 0.9528 in
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Bach 15D has a cup diameter of 24.40 mm / 0.9606 in compared to 24.20 mm / 0.9528 in on the Bach 18 — a difference of 0.20 mm / 0.0079 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.