Recently I took advantage of a quite Friday afternoon to create an experiment/demonstration of a low frequency resonance being excited on the ESPEC Qualmark RS system. I took three different lengths of 3/8" all-thread rod and fixtured them parallel to the table top. I put masses on the ends of the rods to shift the resonant frequencies down. Take a look at the video to see the results, and feel free to post any comments or questions below.
Thanks for watching! And remember - if it isn't broken, you're not done yet!