Which has a bigger cup — Bach 18 or Kelly 25?

The Bach 18 has a cup diameter of 32.10 mm / 1.2638 in compared to 30.99 mm / 1.2201 in on the Kelly 25 — a difference of 1.11 mm / 0.0437 in. A wider cup generally produces a fuller, darker tone but requires more air support.

How does cup depth compare between Bach 18 and Kelly 25?

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

Bach 18 vs Kelly 25

Name: Kelly 25
Brand: Kelly

The Bach 18 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 18

• Tuba

Backbore—

Best suited for

📣High-volume projection — open throat for power

Mouthpiece B

Kelly 25

• Tuba

General

BackboreM

Best suited for

📋General tuba / euphonium doubler

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.