Bach 12E vs Yamaha SL-51C4S
The Yamaha SL-51C4S has a wider cup diameter, the Yamaha SL-51C4S features a deeper cup, the Yamaha SL-51C4S has a larger throat opening.
Cup Diameter
The Yamaha SL-51C4S has a cup diameter of 25.23 mm / 0.9933 in compared to 24.50 mm / 0.9646 in on the Bach 12E — a difference of 0.73 mm / 0.0287 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Yamaha SL-51C4S has a medium cup while the Bach 12E has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
The Yamaha SL-51C4S has a wider throat (6.92 mm / 0.2724 in vs 5.85 mm / 0.2303 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.