Bach 8½A vs Yamaha CR-9ES
The Yamaha CR-9ES has a wider cup diameter, the Yamaha CR-9ES has a larger throat opening.
Cup Diameter
The Yamaha CR-9ES has a cup diameter of 16.44 mm / 0.6472 in compared to 16.10 mm / 0.6339 in on the Bach 8½A — a difference of 0.34 mm / 0.0134 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a very deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Yamaha CR-9ES has a wider throat (4.50 mm / 0.1772 in vs 3.66 mm / 0.1441 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.