Bach 18 vs Bruno Tilz 230-D 2
The Bach 18 has a wider cup diameter, the Bach 18 has a larger throat opening.
Cup Diameter
The Bach 18 has a cup diameter of 32.10 mm / 1.2638 in compared to 31.00 mm / 1.2205 in on the Bruno Tilz 230-D 2 — a difference of 1.10 mm / 0.0433 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 Bach 18 has a wider throat (9.00 mm / 0.3543 in vs 6.50 mm / 0.2559 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.