Although non-octave music is not a well-known subject among composers or musicologists, “the avoidance of octave doubling” was deemed especially important by the Modernist composer Arnold Schoenberg. This article introduces composers and performers to two non-octave tunings invented by a German engineer named Heinz Bohlen plus two octave-based tunings that can be used to approximate Bohlen’s tunings. The principal aim is to encourage further practical experiments, not to indulge in phenomenological speculation. Relevant texts by William Brouncker, Walter O’Connell and Kees van Prooijen are briefly discussed.