Yamaha Tuba Model No. Inner Rim Diameter (mm) Rim Contour/ Thickness Cup Depth Throat (mm) Backbore Playing Characteristics 64 30.45 standard/ thick standard 8.35 standard Small inner rim diameter with a medium cup. An ideal beginner's model for young players. Well-balanced rim configuration for flexibility and easy playability. 65 30.95 standard/ semi-thin standard 8.35 semi-wide Relatively small inner rim diameter and medium cup volume for easy playability. Excellent balance throughout the instrument's range, with a fairly dark tone. 66B 31.37 standard/ standard semi-shallow 8.35 semi-wide Shallower cup than the 66. Outstanding playability and flexibility. Fairly bright tone and facile response over a wide range. 66 31.37 standard/ standard standard 8.35 standard Voluminous cup. Fairly dark tone with plenty of power. Excellent resonance and clarity. Popular in ensembles and orchestras. 66D4 31.49 semi-flat/ semi-thick semi-deep 8.87 semi-wide Excellent matching with Eb brass band instruments. Very deep cup. Dark tone with plenty of volume. Symphonic sound. 67B4 32.06 semi-flat/ semi-thick semi-shallow 7.02 standard Large inner rim diameter with a shallow cup. Easy playability with a bright tone. Particularly easy high notes and clear lows. Perfect for F instruments. 67 31.93 standard/ standard standard 8.35 semi-wide Exceptional rim and cup balance for easy playability. Good match for Bb, C, and Eb instruments. Well-centered tone. 67C4 32.06 semi-flat/ semi-thick standard 8.10 standard A perfect match for Bb and C instruments. All-around versatility. Smooth, mellow tone throughout the instrument's range. Plenty of volume and power. 68B 32.72 standard/ semi-thick semi-shallow 7.50 standard Large inner rim diameter with a small cup volume and throat. Enhanced clarity in large Bb and C tubas.