The first devices Dr. Gavreau implemented were designed to imitate the "accident" which first made his research group aware of infrasonics. They designed real organ pipes of exceedingly great width and length. The first of these was six feet in diameter and seventy five feet long. These designs were tested outdoors, securely propped against protective sound-absorbent walls. The investigators stood at a great distance. Two forms of these infrasonic organ pipes were built. The first utilized a drive piston which pulsed the pipe output. The second utilized compressed air in a more conventional manner.
The main resonant frequency of these pipes occurred in the "range of death", found to lie between three and seven cycles per second. These sounds could not be humanly heard, a distinct advantage for a defense system. The effects were felt however. The symptoms come on rapidly and unexpectedly, though the pipes were operating for a few seconds. Their pressure waves impacted against the entire body in a terrible and inescapable grip. The grip was a pressure which came in on one from all sides simultaneously, an envelope of death.
Next came the pain, dull infrasonic pressure against the eyes and ears. Then came a frightening manifestation on the material supports of the device itself. With sustained operation of the pipe, a sudden rumble rocked the area, nearly destroying the test building. Every pillar and joint of the massive structure bolted and moved. One of the technicians managed to ignore the pain enough to shut down the power supply.
An envelope of death. Hmm. These things are huge, but if someone built enough of them around a major city, disabled communications and such with EMPs, it could be pretty devastating. It could kill everyone within a 5 mile radius within a few seconds. And destroy buildings/infrastructure. Plus be remotely activated.
EDIT: oh yeah, someone mentioned using sections of sewage pipe or drainage pipe, said they'd successfully created infrasound generators this way. I suppose you'd want to block off a section around 75 in length, with your equipment at the blocked end so that the open end is pointed towards the city, buildings, etc. Actually sounds a lot more reasonable now that I think about it. No need to build massive pipes. Just hijack existing ones.
EDIT2:
In an attempt to achieve more compact and controllable infrasound generators, Dr. Gavreau designed and tested special horns and "whistles" of various volumes. These were each remarkably simple flat circular resonant cavities, having a side output duct. They were simply the large analogues of foghorns and police whistles. These flat forms were volumetrically reduced in successive design stages because it was found that their output was far too great. The infrasonic foghorns could produce a frightening two kilowatts of infrasonic energy, at a pitch of one hundred fifty cycles per second.
The flat "police whistles" were more easily designed to required specifications. Their overall characteristics were quite simple to determine, a mathematical formula being devised for the purpose. The whistle’s resonant pitch was found by dividing its diameter into a numerical constant of 51. Increasing the depth of the whistle effectively increased its amplitude. A whistle 1.3 meters in diameter produced an infrasonic pitch of 37 cycles per second. This form violently shook the walls of the entire laboratory complex, though its intensity was less than 2 watts infrasonic power.
Aaaand the compact form.
Tesla often went to great lengths in describing the effects of infrasounds to newspaper reporters who, behind his back, scoffed at the notion that a "little sound" could effect such devastations. Yet, it was precisely with such a "little sound" that Tesla nearly brought down his laboratory on Houston Street. His compact infrasonic impulsers were terribly efficient. Tesla later designed and tested infrasonic impulse weapons capable of wrecking buildings and whole cities on command.
Whole cities you don't sayyyy
“The US military was playing with a helicopter mounted sonic device back in the 70’s I think. You dropped a pickup on top of a concrete pill box, three helicopters would position out of range
and bombard the pill pox with a sine wave. Once the resonant freq was dialed in, the concrete crumbled to dust in a minute or two. Very effective but dange-rous as a minute is an eternity on a battlefield.”
Gasoline trucks are basically just giant bombs. You could also pour the fuel down the sewers to see what infrastructure gets rekt when it ignites.