Bach 6BM vs Bach 8½A
The Bach 6BM has a wider cup diameter, the Bach 8½A features a deeper cup, the Bach 6BM has a larger throat opening.
Cup Diameter
The Bach 6BM has a cup diameter of 16.20 mm / 0.6378 in compared to 16.10 mm / 0.6339 in on the Bach 8½A — a difference of 0.10 mm / 0.0039 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Bach 8½A has a very deep cup while the Bach 6BM has a deep cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Bach 6BM 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.