Bach 15CW vs Yamaha SL-48S-GP
The Yamaha SL-48S-GP has a wider cup diameter, the Yamaha SL-48S-GP features a deeper cup, the Yamaha SL-48S-GP has a larger throat opening.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 15CW
• Trombone
Cup diameter24.40 mm / 0.9606 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Yamaha SL-48S-GP
• Trombone
Cup diameter25.25 mm / 0.9941 in
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Yamaha SL-48S-GP has a cup diameter of 25.25 mm / 0.9941 in compared to 24.40 mm / 0.9606 in on the Bach 15CW — a difference of 0.85 mm / 0.0335 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.