This Bass Xylophone add-on is used together with your diatonic Orff instruments to form full chromatic xylophones. Order these instruments after your students have become sufficiently skilled on the diatonic Orff instruments. The chromatic keyboards come with resonator box and 2 C# 2 D# & 2 G# bars. Combine the spare Bb & 2 F# bars from your diatonic instruments with the chromatic notes to form full chromatic keyboards.