Bob Reeves 11C vs Kelly 12C
The Bob Reeves 11C has a wider cup diameter.
Mouthpiece A
Bob Reeves 11C
• Trombone
Cup diameter24.80 mm / 0.9764 in
Cup depthShallow
Rim width—
Throat diameter—
Backbore—
Finish—
Material—
vs
Mouthpiece B
Kelly 12C
• Trombone
LeadCup diameter24.13 mm / 0.9500 in
Cup depthShallow
Rim width—
Throat diameter—
BackboreS
Finish—
MaterialLexan polycarbonate
Best suited for
Lead trombone; smallest cup
Cup Diameter
The Bob Reeves 11C has a cup diameter of 24.80 mm / 0.9764 in compared to 24.13 mm / 0.9500 in on the Kelly 12C — a difference of 0.67 mm / 0.0264 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a shallow cup depth, so the sound character from depth alone will be very similar.
Material
The Bob Reeves 11C is described as unspecified, and the Kelly 12C as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
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.