Yamaha CR-11A4L vs Yamaha CR-11B4L
The Yamaha CR-11B4L has a wider cup diameter, the Yamaha CR-11B4L features a deeper cup.
Cup Diameter
The Yamaha CR-11B4L has a cup diameter of 16.64 mm / 0.6551 in compared to 15.99 mm / 0.6295 in on the Yamaha CR-11A4L — a difference of 0.65 mm / 0.0256 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Yamaha CR-11B4L has a shallow cup while the Yamaha CR-11A4L has a very shallow 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 3.65 mm / 0.1437 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.