You may or may not know, dear reader, that I've been poking at the problem of creating physical low-frequency resonance for some time now. I've tried a few things, including a subwoofer-driven Helmholtz resonator thrown together from Sono Tubes and Duct Tape (indeterminate results, some possibilities).
I fell back, during past haunts, on using bass-shakers bolted to the crawl tunnels and hand-tuning the frequency generator to get a good subsonic. When that works, it's an amazing and beautiful thing (people refused to go in on early tests, it "just felt weird"). Sadly, that system of open-loop resonance falls out of tune too easily. I should add a microphone or other sonic transducer to it and make it closed loop, and then I'll melt your brain in the tunnels! Bwahahahahahah!
::ahem::
Today, however, I finally succeeded in making an air-powered resonator out of about 32-feet of 4.5" diameter sewer pipe (and some duct tape, of course). It... resonated! First it squawks like a demon-tormented goose, and then if rumbles and shifts and then... tones! Not pure, but pretty nifty nonetheless.
An eight foot pipe produces a surprisingly high tone, and 32 feet of it isn't as low as I would like. However, there are a zillion things to tune -- airflow, back pressure (once I build a back-pressure chamber), elasticity of the membrane, sealing characteristics of the driving tube, and most important for good low frequency amplitude, diameter.
Yup yup yup... maybe a switchback of forty feet of 12" sono tube with tubable back pressure and a durable membrane... mmmmmmm yeah.
Posted by Edwin at July 6, 2008 05:09 PM