Bach 4 vs Schilke 53
The Schilke 53 has a wider cup diameter, the Schilke 53 has a larger throat opening.
Cup Diameter
The Schilke 53 has a cup diameter of 26.24 mm / 1.0331 in compared to 26.00 mm / 1.0236 in on the Bach 4 — a difference of 0.24 mm / 0.0094 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 Schilke 53 has a wider throat (5.95 mm / 0.2343 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.