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Bach 1B vs Kelly 4B-UK

The Bach 1B has a wider cup diameter, the Kelly 4B-UK features a deeper cup, the Kelly 4B-UK has a larger throat opening.

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
    Bach 1B
    • Cornet
    Cup diameter17.00 mm / 0.6693 in
    Best suited for
    🎻Orchestral playing — large cup for full, dark tone
    vs
    Mouthpiece B
      Kelly 4B-UK
      • Cornet
      Orchestral
      Cup diameter16.51 mm / 0.6500 in
      Best suited for
      📣High-volume projection — open throat for power
      📋Professional cornet; British brass band

      Cup Diameter

      The Bach 1B has a cup diameter of 17.00 mm / 0.6693 in compared to 16.51 mm / 0.6500 in on the Kelly 4B-UK — a difference of 0.49 mm / 0.0193 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 Bach 1B details Kelly 4B-UK details Bach 1B equivalents Kelly 4B-UK equivalents

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