Which has a bigger cup — Bach 17C or Kelly 51D-EU?

The Kelly 51D-EU has a cup diameter of 25.40 mm / 1.0000 in compared to 24.20 mm / 0.9528 in on the Bach 17C — a difference of 1.20 mm / 0.0472 in. A wider cup generally produces a fuller, darker tone but requires more air support.

How does cup depth compare between Bach 17C and Kelly 51D-EU?

The Kelly 51D-EU has a — cup while the Bach 17C has a shallow cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.

Bach 17C vs Kelly 51D-EU

Name: Kelly 51D-EU
Brand: Kelly

The Kelly 51D-EU has a wider cup diameter, the Kelly 51D-EU features a deeper cup.

Overall Comparison Cup Diameter Cup Depth Rim Width Throat Diameter Backbore Finish Material

The narrowest point at the bottom of the cup. Affects resistance, volume, and tone color.

Mouthpiece A

Bach 17C

• Baritone / Euphonium

Throat diameter5.85 mm / 0.2303 in

Best suited for

📣High-volume projection — open throat for power

Mouthpiece B

Kelly 51D-EU

• Baritone / Euphonium

Professional

Throat diameter—

Best suited for

🎻Orchestral playing — large cup for full, dark tone

📋Professional euphonium

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.

Open in interactive tool + Add third mouthpiece Bach 17C details Kelly 51D-EU details Bach 17C equivalents Kelly 51D-EU equivalents

Bach 17C vs Kelly 51D-EU

Playing Characteristics

What Do These Model Names Mean?

What Changes If You Switch?

Which is better?

Compare Bach 17C with others

Compare Kelly 51D-EU with others

Popular Baritone / Euphonium comparisons

Bach vs Kelly

Browse by specification