Bach 4 vs Denis Wick 6BM
The Bach 4 has a wider cup diameter, the Denis Wick 6BM has a larger throat opening.
Cup Diameter
The Bach 4 has a cup diameter of 26.00 mm / 1.0236 in compared to 25.40 mm / 1.0000 in on the Denis Wick 6BM — a difference of 0.60 mm / 0.0236 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 Denis Wick 6BM has a wider throat (7.12 mm / 0.2803 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.