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 width of the rim surface that contacts the lips. Wider rims improve endurance; narrower rims improve flexibility.

Mouthpiece A

Bach 12E

• Trombone

Rim width—

Best suited for

📣High-volume projection — open throat for power

Mouthpiece B

Kelly SKY-SS

• Trombone

Lead

Rim width—

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.