Bach 18 vs Giardinelli 6M
The Giardinelli 6M has a wider cup diameter, the Bach 18 has a larger throat opening.
Cup Diameter
The Giardinelli 6M has a cup diameter of 24.50 mm / 0.9646 in compared to 24.20 mm / 0.9528 in on the Bach 18 — a difference of 0.30 mm / 0.0118 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 18 has a wider throat (5.85 mm / 0.2303 in vs 5.75 mm / 0.2264 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.