Bach 15 vs Bach 18
The Bach 15 has a wider cup diameter.
Mouthpiece A
Bach 15
• French Horn
Cup diameter16.30 mm / 0.6417 in
Cup depthMedium
Rim width—
Throat diameter4.50 mm / 0.1772 in
Backbore—
Finish—
Material—
Best suited for
All-round versatile — balanced cup for general playing
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 18
• French Horn
Cup diameter16.15 mm / 0.6358 in
Cup depthMedium
Rim width—
Throat diameter4.50 mm / 0.1772 in
Backbore—
Finish—
Material—
Best suited for
All-round versatile — balanced cup for general playing
High-volume projection — open throat for power
Cup Diameter
The Bach 15 has a cup diameter of 16.30 mm / 0.6417 in compared to 16.15 mm / 0.6358 in on the Bach 18 — a difference of 0.15 mm / 0.0059 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
Throat diameters are essentially identical at 4.50 mm / 0.1772 in, so resistance feel will be comparable.
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.