Bach 8½A vs Conn Imp. Precision 4
The Conn Imp. Precision 4 has a wider cup diameter, the Bach 8½A features a deeper cup.
Cup Diameter
The Conn Imp. Precision 4 has a cup diameter of 16.41 mm / 0.6461 in compared to 16.10 mm / 0.6339 in on the Bach 8½A — a difference of 0.31 mm / 0.0122 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 Conn Imp. Precision 4 has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Material
The Bach 8½A is described as unspecified, and the Conn Imp. Precision 4 as Silver-plated brass. 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.