Kelly 7C vs Marcinkiewicz 10
The Marcinkiewicz 10 has a wider cup diameter, the Marcinkiewicz 10 features a deeper cup, the Marcinkiewicz 10 has a larger throat opening.
Cup Diameter
The Marcinkiewicz 10 has a cup diameter of 16.84 mm / 0.6630 in compared to 16.51 mm / 0.6500 in on the Kelly 7C — a difference of 0.33 mm / 0.0130 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Marcinkiewicz 10 has a deep cup while the Kelly 7C has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Marcinkiewicz 10 has a wider throat (3.73 mm / 0.1469 in vs 3.66 mm / 0.1441 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Kelly 7C is described as Lexan polycarbonate, and the Marcinkiewicz 10 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.