Bach 4 vs Kelly 5G-EU-SS

The Bach 4 has a wider cup diameter, the Kelly 5G-EU-SS features a deeper cup.

Overall Comparison Cup Diameter Cup Depth Rim Width Throat Diameter Backbore Finish Material
Mouthpiece A
    Bach 4
    • Baritone / Euphonium
    Cup diameter26.00 mm
    Cup depthMedium
    Rim width
    Throat diameter5.85 mm
    Backbore
    Finish
    Material
    Best suited for
    📣High-volume projection — open throat for power
    vs
    Mouthpiece B
      Kelly 5G-EU-SS
      • Baritone / Euphonium
      General
      Cup diameter25.40 mm
      Cup depth
      Rim width
      Throat diameter
      BackboreL
      Finish
      Material316 Surgical Stainless Steel
      Best suited for
      🎻Orchestral playing — large cup for full, dark tone
      📋Euphonium general use

      Cup Diameter

      The Bach 4 has a cup diameter of 26.00 mm compared to 25.40 mm on the Kelly 5G-EU-SS — a difference of +0.60 mm. A wider cup generally produces a fuller, darker tone but requires more air support.

      Cup Depth

      The Kelly 5G-EU-SS has a — cup while the Bach 4 has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.

      Material

      The Bach 4 is described as unspecified, and the Kelly 5G-EU-SS as 316 Surgical Stainless Steel. 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.

      Open in interactive tool + Add third mouthpiece Bach 4 details Kelly 5G-EU-SS details Bach 4 equivalents Kelly 5G-EU-SS equivalents