Bruno Tilz 211-58 F vs Kelly 31
The Kelly 31 has a wider cup diameter, the Kelly 31 features a deeper cup.
Cup Diameter
The Kelly 31 has a cup diameter of 17.53 mm compared to 17.00 mm on the Bruno Tilz 211-58 F — a difference of +0.53 mm. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Kelly 31 has a — cup while the Bruno Tilz 211-58 F has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 3.80 mm, so resistance feel will be comparable.
Material
The Bruno Tilz 211-58 F is described as unspecified, and the Kelly 31 as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
Which is better?
The Bruno Tilz 211-58 F is designed for catalog playing, while the Kelly 31 targets general use. Your best choice depends on your musical context.