A pulse jet becomes an insane trombone with a slide to change the length of the exhaust pipe.
First experiments with this was done by Tobias Lukassen and I at illutron, after I had been doing various experiments with getting propane to explode in different ways.
I started out doing a "plumbers pulse jet" using standard pipe fittings. That made it easy to play around with different configurations of pipe. Doing that, I noticed how different pipe length gave different tone to the "noise"/"sound" of the pulse jet.
Later this evolved into the pulse jet trombone concerts with Lars Kynde and others.