Hi: I'm watching this hour lecture on YouTube by the Naval Postgraduate School (NPS) for information about Helmholtz Resonators, but recommend it here because there's excellent demonstrations of time related ideas. Helmholtz Resonator and other Maintained Oscillators https://youtu.be/y86QhzesYok -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html