Bach 10 vs Yamaha HR-32D4
The Yamaha HR-32D4 has a wider cup diameter, the Bach 10 features a deeper cup.
Cup Diameter
The Yamaha HR-32D4 has a cup diameter of 17.48 mm / 0.6882 in compared to 16.80 mm / 0.6614 in on the Bach 10 — a difference of 0.68 mm / 0.0268 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Bach 10 has a very deep cup while the Yamaha HR-32D4 has a deep cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 4.50 mm / 0.1772 in, so resistance feel will be comparable.
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.