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Kelly 12C vs Yamaha SL-48L-GP

The Yamaha SL-48L-GP has a wider cup diameter, the Yamaha SL-48L-GP features a deeper cup.

Overall Comparison Cup Diameter Cup Depth Rim Width Throat Diameter Backbore Finish Material
The internal diameter of the cup, measured at the widest point inside the rim.
Mouthpiece A
    Kelly 12C
    • Trombone
    Lead
    Cup diameter24.13 mm / 0.9500 in
    Best suited for
    📋Lead trombone; smallest cup
    vs
    Mouthpiece B
      Yamaha SL-48L-GP
      • Trombone
      Cup diameter25.25 mm / 0.9941 in
      Best suited for
      📣High-volume projection — open throat for power

      Cup Diameter

      The Yamaha SL-48L-GP has a cup diameter of 25.25 mm / 0.9941 in compared to 24.13 mm / 0.9500 in on the Kelly 12C — a difference of 1.12 mm / 0.0441 in. A wider cup generally produces a fuller, darker tone but requires more air support.

      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.

      Open in interactive tool + Add third mouthpiece Kelly 12C details Yamaha SL-48L-GP details Kelly 12C equivalents Yamaha SL-48L-GP equivalents

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