Kelly 18 vs Marcinkiewicz CH W1
The Marcinkiewicz CH W1 has a wider cup diameter, the Kelly 18 features a deeper cup.
Cup Diameter
The Marcinkiewicz CH W1 has a cup diameter of 33.66 mm / 1.3252 in compared to 32.77 mm / 1.2902 in on the Kelly 18 — a difference of 0.89 mm / 0.0350 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 18 has a — cup while the Marcinkiewicz CH W1 has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Material
The Kelly 18 is described as Lexan polycarbonate, and the Marcinkiewicz CH W1 as unspecified. 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.