Bach 12 vs Yamaha HR-SOMMERVILLE
The Yamaha HR-SOMMERVILLE has a wider cup diameter, the Bach 12 has a larger throat opening.
Cup Diameter
The Yamaha HR-SOMMERVILLE has a cup diameter of 16.93 mm / 0.6665 in compared to 16.50 mm / 0.6496 in on the Bach 12 — a difference of 0.43 mm / 0.0169 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a medium cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Bach 12 has a wider throat (4.50 mm / 0.1772 in vs 4.30 mm / 0.1693 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.