In the beginning, God created the heaven and the earth. Sometime later, as a kid, I was watching The Muppet Show when I witnessed a skit with actress Jean Stapleton (of Archie Bunker fame) and the Muppet named Crazy Harry. In the skit, Harry claims to be playing an "instrument" called the Explodophone. Ms. Stapleton sings "I'm Just Wild About Harry" and dances about the Grecco-industrial set while Harry pushes plungers on dynamos, setting off pyrotechnic charges at specific times with the music.
Part of the joke was the doubtful legitimacy of the "Explodophone", which seemed an excuse to blow stuff up, Harry's favorite pastime. But the Explodophone was actually used as a percussion instrument to punctuate pauses in the music. The charges were also choreographed to create visual interest, framed in each shot that followed Ms. Stapleton's dance.
I also recall the wonderful description of the fictional band Disaster Area in The Hitchhiker's Guide To The Galaxy, which was best heard "from within large concrete bunkers some thirty-seven miles away from the stage, whilst the musicians themselves played their instruments by remote control from within a heavily insulated spaceship which stayed in orbit around the planet - or more frequently around a completely different planet."
Years later, while watching an experimental music exhibition at the University of Utah, I was discussing a performance with a friend. Eight performers knocked pieces of lacquered wood together in rhythm. I struggled to enjoy the piece. My friend said he found it boring, because he was bored by percussive instruments that had no variation in pitch.
While an undergrad at Brigham Young University, I enjoyed listening to lunchtime concerts at the Carillon Bell Tower. This fermented with these other experiences to lead me to brainstorm about other massive instruments. The primary idea to come out of this was the Nuclear Steam Calliope, a steam whistle powered by a uranium reactor. To save money, instead of organ-like pipes, it would use a single vertical concrete tube that had holes at intervals like a large tin whistle. The holes could be covered in different combinations for different pitches.
Yet later, I was watching a video (sorry, can't find it) by Bay Area performance artists Survival Research Laboratories that blew stuff up with a device called The Shockwave Cannon. This used focused shockwaves from propane explosions to blow apart dolls, windows, a model house, and various other things, and it was remotely controlled by people on the Web. It came to me that tuned explosions could strike recognizable notes, turning the "boring" Explodophone into a tonal percussive instrument that would be interesting.
Scaling it back umpteen times, I hit upon using toy caps for controlled explosions and empty Pringle's potato chip cans for tuning. I cut the cans to a few different lengths, creating the Explodophone 0.1. I then inflicted an impromptu concert on my siblings for the Fourth of July one year. I arranged the cans upright on a table, then fired the cap gun into the mouth of the appropriately-sized tube for each note. The tune was something very simple, like "Mary Had A Little Lamb" or something, and there were many misfires. Afterwards, I sought feedback from a stunned audience. One remarked that they didn't expect an actual tune, but there it was. That was all the encouragement I needed. I had created a tonal percussive instrument using explosions. It was no longer "boring".
UPDATE: Since publishing this log, I have become aware of few related ideas out there. I failed to acknowledge the inspiration of SRL's hovercraft, which was propelled by a pair of twin pulsejets that are slightly detuned to create a very loud, musical throb when fired together. I also recently learned of the pyrophone, a concept similar to the Explodophone. Also, I stumbled across an issue of New Scientist from February 1973 where columnist "Daedalus" outlines a device he calls the Explodophone, or Internal Combustion Bassoon. (There is a follow-up mention here.) This would use many carefully timed explosions to resonate at a note, similar to a valveless pulsejet. Note that pyrophones and pulsejets all operate continuously and can be played "legato"; my Explodophone is a discrete pulsed device that must be played "staccato."