Date: 1924. (Drawing)
The Wonderphone family of double bell front Euphoniums consists of the 56I/57I (picture here), 58I/59I and the 60I/61I (see separate listing). The 56I/57I are four valve top action instruments. The 58I/59I are four valve front action instruments. The 60I/61I are five valve front action instruments. Even numbered instruments are low pitch, odd numbered instruments are high pitch.
What Conn said in 1924:
In these models are combined the advantages of the curved bell, which is adjustable and detachable, and the extra bell, which enables the performer to use echo or trombone effects to give variety and life to the tone coloring. In one sense, therefore, these instruments represent the highest development in Euphonium improvements, for there is nothing lacking. To the smooth, accurately proportioned sound passages resulting from the hydraulic expansion process of manufacture has been added the famous Conn light acting valve mechanism.