Bach 5V vs Kelly 6V
The Bach 5V has a wider cup diameter, the Kelly 6V features a deeper cup, the Bach 5V has a larger throat opening.
Cup Diameter
The Bach 5V has a cup diameter of 16.25 mm / 0.6398 in compared to 16.00 mm / 0.6299 in on the Kelly 6V — a difference of 0.25 mm / 0.0098 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 5V has a very deep cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Bach 5V has a wider throat (4.09 mm / 0.1610 in vs 4.06 mm / 0.1598 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Material
The Bach 5V 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.