Which has a bigger cup — Bach 12E or Kelly SKY-SS?

The Kelly SKY-SS has a cup diameter of 24.64 mm / 0.9701 in compared to 24.50 mm / 0.9646 in on the Bach 12E — a difference of 0.14 mm / 0.0055 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 SKY-SS?

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

Bach 12E vs Kelly SKY-SS

Name: Kelly SKY-SS
Brand: Kelly

The Kelly SKY-SS 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 SKY-SS

• Trombone

Lead

BackboreS

Best suited for

📋Professional lead trombone

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.