Bach 10 vs Marcinkiewicz 15
The Marcinkiewicz 15 has a wider cup diameter, the Marcinkiewicz 15 has a larger throat opening.
Cup Diameter
The Marcinkiewicz 15 has a cup diameter of 17.42 mm / 0.6858 in compared to 16.80 mm / 0.6614 in on the Bach 10 — a difference of 0.62 mm / 0.0244 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a very deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Marcinkiewicz 15 has a wider throat (4.57 mm / 0.1799 in vs 4.50 mm / 0.1772 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.