Bach 12E vs Kelly SYMPHONY-LS-SS
The Kelly SYMPHONY-LS-SS has a wider cup diameter, the Kelly SYMPHONY-LS-SS features a deeper cup.
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
Bach 12E
• Trombone
Cup diameter24.50 mm / 0.9646 in
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Kelly SYMPHONY-LS-SS
• Trombone
OrchestralCup diameter25.65 mm / 1.0098 in
Best suited for
Orchestral playing — large cup for full, dark tone
Symphonic trombone
Cup Diameter
The Kelly SYMPHONY-LS-SS has a cup diameter of 25.65 mm / 1.0098 in compared to 24.50 mm / 0.9646 in on the Bach 12E — a difference of 1.15 mm / 0.0453 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.