Bach 8½A vs Kelly 6V
The Bach 8½A has a wider cup diameter, the Kelly 6V features a deeper cup, the Kelly 6V has a larger throat opening.
Cup Diameter
The Bach 8½A has a cup diameter of 16.10 mm / 0.6339 in compared to 16.00 mm / 0.6299 in on the Kelly 6V — 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 Kelly 6V has a — cup while the Bach 8½A has a very deep cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Kelly 6V has a wider throat (4.06 mm / 0.1598 in vs 3.66 mm / 0.1441 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Bach 8½A is described as unspecified, and the Kelly 6V as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
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.