If there were a musical equivalent of alternative history writing, Harry Partch would be its best-known author. A hobo in his teen years during the 1920s, Partch grew up to be one of the twentieth century's greatest speculative composers, who created his own set of 27 new instruments that could be played in his specially-designed symphony space. Influenced by the tonal scales of Asian and Native American music, Partch's instruments use the "Just Intonation" scale, which is composed of 29 tones. This scale is a more direct reflection of the tones we hear in nature, and was used quite commonly in the West before the 12 tone scale (which you know from pianos) was invented about 250 years ago.
Partch's idea was to return to a more natural set of musical sounds, but unfortunately all Western instruments are set up to use the 12-tone scale. So he just invented his own new orchestra that used the Just Intonation scale, including instruments called the "harmonic canon," the "chromelodeon," the "boo," the "quadrangularus reversum" and (my personal favorite) the "spoils of war." Many of these instruments make sounds that will remind you of classical Chinese music, and in some cases African music.
Essentially, Partch imagined an alternate history of Western music, in which composers never abandoned the Just Intonation scale, and instrument-makers used materials like bamboo in their work to create a more Asian sound.
The best part is that you can not only hear the alternate history orchestra, you can play in it. American Public Media has an amazing multimedia site devoted to Harry Partch, complete with Flash thingers that let you play Partch's instruments with your mouse or keyboard. I spent quite a while zooming all over the nernnerners and boops and KLARNGs of Partch's orchestra, and it was damn fun. Highly recommended if you want to experience the speculative side of music-making. Image by Michelle V. Agins/The New York Times.