Bach 1 vs Yamaha TR-15E4
The Bach 1 has a wider cup diameter, the Yamaha TR-15E4 has a larger throat opening.
Cup Diameter
The Bach 1 has a cup diameter of 17.50 mm / 0.6890 in compared to 16.92 mm / 0.6661 in on the Yamaha TR-15E4 — a difference of 0.58 mm / 0.0228 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 TR-15E4 has a wider throat (3.88 mm / 0.1528 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.