Which has a bigger cup — Bach 12E or Kelly 12C?

The Bach 12E has a cup diameter of 24.50 mm / 0.9646 in compared to 24.13 mm / 0.9500 in on the Kelly 12C — a difference of 0.37 mm / 0.0146 in. A wider cup generally produces a fuller, darker tone but requires more air support.

How does cup depth compare between Bach 12E and Kelly 12C?

Both mouthpieces share a shallow cup depth, so the sound character from depth alone will be very similar.

Bach 12E vs Kelly 12C

Name: Kelly 12C
Brand: Kelly

The Bach 12E has a wider cup diameter.

Overall Comparison Cup Diameter Cup Depth Rim Width Throat Diameter Backbore Finish Material

The taper behind the throat leading to the shank. Affects projection and tone character.

Mouthpiece A

Bach 12E

• Trombone

Backbore—

Best suited for

📣High-volume projection — open throat for power

Mouthpiece B

Kelly 12C

• Trombone

Lead

BackboreS

Best suited for

📋Lead trombone; smallest cup

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.