Bach 19 vs Yamaha SL-48DL
The Yamaha SL-48DL has a wider cup diameter, the Yamaha SL-48DL has a larger throat opening.
Cup Diameter
The Yamaha SL-48DL has a cup diameter of 25.25 mm / 0.9941 in compared to 24.00 mm / 0.9449 in on the Bach 19 — a difference of 1.25 mm / 0.0492 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Yamaha SL-48DL has a wider throat (6.62 mm / 0.2606 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.