Bach 18 vs Giardinelli C12
The Giardinelli C12 has a wider cup diameter, the Giardinelli C12 has a larger throat opening.
Cup Diameter
The Giardinelli C12 has a cup diameter of 17.50 mm / 0.6890 in compared to 16.15 mm / 0.6358 in on the Bach 18 — a difference of 1.35 mm / 0.0531 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 Giardinelli C12 has a wider throat (4.80 mm / 0.1890 in vs 4.50 mm / 0.1772 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.