Marcinkiewicz 18 vs Marcinkiewicz ETU1J. Self
The Marcinkiewicz ETU1J. Self has a wider cup diameter, the Marcinkiewicz 18 has a larger throat opening.
Cup Diameter
The Marcinkiewicz ETU1J. Self has a cup diameter of 33.15 mm / 1.3051 in compared to 32.77 mm / 1.2902 in on the Marcinkiewicz 18 — a difference of 0.38 mm / 0.0150 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a medium cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Marcinkiewicz 18 has a wider throat (8.20 mm / 0.3228 in vs 8.03 mm / 0.3161 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
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.