Bach 10 vs Yamaha HR-31B
The Yamaha HR-31B has a wider cup diameter, the Bach 10 features a deeper cup, the Bach 10 has a larger throat opening.
Cup Diameter
The Yamaha HR-31B has a cup diameter of 17.47 mm / 0.6878 in compared to 16.80 mm / 0.6614 in on the Bach 10 — a difference of 0.67 mm / 0.0264 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-31B has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Bach 10 has a wider throat (4.50 mm / 0.1772 in vs 3.90 mm / 0.1535 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.