Bach 12C vs Yamaha SL-51BL
The Yamaha SL-51BL has a wider cup diameter, the Yamaha SL-51BL has a larger throat opening.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 12C
• Trombone
Cup diameter24.50 mm / 0.9646 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Yamaha SL-51BL
• Trombone
Cup diameter25.23 mm / 0.9933 in
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Yamaha SL-51BL has a cup diameter of 25.23 mm / 0.9933 in compared to 24.50 mm / 0.9646 in on the Bach 12C — a difference of 0.73 mm / 0.0287 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.