Bach 18D vs Yamaha AH-37C4
The Bach 18D has a wider cup diameter, the Yamaha AH-37C4 features a deeper cup, the Bach 18D has a larger throat opening.
Cup Diameter
The Bach 18D has a cup diameter of 24.20 mm compared to 18.60 mm on the Yamaha AH-37C4 — a difference of +5.60 mm. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Yamaha AH-37C4 has a medium cup while the Bach 18D has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Bach 18D has a wider throat (5.85 mm vs 5.25 mm). 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.