I simply want powerful subsonic frequencies that can be heard a mile away. I don't know why but I guess it's the joker in me that wants to stir up people in thinking there's an earthquake. I dream of having a cube truck with a black curtain hiding the secret contents and when people are least expecting it, provide them with a burst of thunder! I would just hope law enforcement wouldn't make a big deal over it.
The design of using a volatile mixture of gas and air has been devised and is vastly more complex than I would want. If you are interested in the internal combustion speaker, here is a link that may lead you in the right direction: Internal Combustion Speakers. I do know that just a few drops of alcohol, if ignited and channeled appropriately, the sound can be immense. While living in the Philippines, kids (as well as some adults) would make home-made bazooka looking devices using cardboard tubes or pvc pipe, typically 2-3" diameter, with an attached metal can with bottom punctured and then attached to this would be an upper half of a water bottle. The devices would be taped together and though I never saw any accidents, they are apparently dangerous. Within the cap they would place a cigarette lighter igniter. The fuel they used was atomized alcohol or liquid that they'd have to shake for a few second to allow to volatilize. When ready they point their tube, often at passer-byes, especially if foreign, and give them a deafening blast. Those really were loud. I was shocked at how loud they were. As a little test of the air pushed out, I held a plastic water dipper near the end and it blew it to pieces. If I had a 10-year old kid, I surely wouldn't want him playing with one of these! Even though the devices are illegal and sometimes confiscated by police, they're used everywhere, notably around Christmas and New Year.
Though not a subwoofer, this powerful long horn speaker was developed by Wyle Laboratories. At 30kW and 165 db, it may be the loudest though not used to reproduce music. It is claimed that the power of the sound waves is 5 times greater than when the space shuttle takes off. It is used by the U.S. military for battlefield simulations. See Wlye Laboratories "Was 3000" (#1) and Wlye Laboratories "Was 3000" (#2)
For music reproduction probably no one went to the extent of building a masonry subwoofer compression chamber in a basement like Italian gent, Roberto Delle Curti. It's a perfect location for providing shaking since vibration is transferred with greater efficiency than if just through air. There are ports from the basement up through the walls to deliver the impact of 16 X 400W subwoofers. See The Royal Device Audio Room
This is an example of simply stacking, or adding speakers together yet technologically not supplying anything meaningful. Just buy many speakers and hook them together. Nothing ingenious about it. Still, it has to be admired and appreciated, for who wouldn't want to get close up to it if given the opportunity? Dubbed "The Matterhorn" it consists of 40 subwoofers along with 40 X 1000W amplifiers. The Matterhorn
