Bach 2½C vs Marcinkiewicz 306
The Marcinkiewicz 306 has a wider cup diameter, the Bach 2½C features a deeper cup, the Marcinkiewicz 306 has a larger throat opening.
Cup Diameter
The Marcinkiewicz 306 has a cup diameter of 17.20 mm / 0.6772 in compared to 16.40 mm / 0.6457 in on the Bach 2½C — a difference of 0.80 mm / 0.0315 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Bach 2½C has a medium cup while the Marcinkiewicz 306 has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Marcinkiewicz 306 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.
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.