Bach 18 vs Yamaha BB-67
The Bach 18 has a wider cup diameter, the Bach 18 has a larger throat opening.
Mouthpiece A
Bach 18
• Tuba
Cup diameter32.10 mm / 1.2638 in
Cup depthMedium
Rim width—
Throat diameter9.00 mm / 0.3543 in
Backbore—
Finish—
Material—
Best suited for
High-volume projection — open throat for power
vs
Mouthpiece B
Yamaha BB-67
• Tuba
Cup diameter31.93 mm / 1.2571 in
Cup depthMedium
Rim width—
Throat diameter8.35 mm / 0.3287 in
BackboreSemi-wide
Finish—
Material—
Best suited for
High-volume projection — open throat for power
Cup Diameter
The Bach 18 has a cup diameter of 32.10 mm / 1.2638 in compared to 31.93 mm / 1.2571 in on the Yamaha BB-67 — a difference of 0.17 mm / 0.0067 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 (9.00 mm / 0.3543 in vs 8.35 mm / 0.3287 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.