Bach 12E vs Bruno Tilz 306-1 1/2 C
The Bruno Tilz 306-1 1/2 C has a wider cup diameter, the Bruno Tilz 306-1 1/2 C has a larger throat opening.
Cup Diameter
The Bruno Tilz 306-1 1/2 C has a cup diameter of 27.00 mm / 1.0630 in compared to 24.50 mm / 0.9646 in on the Bach 12E — a difference of 2.50 mm / 0.0984 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a shallow cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Bruno Tilz 306-1 1/2 C has a wider throat (7.00 mm / 0.2756 in vs 5.85 mm / 0.2303 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.