I gave the above demonstration of my self-built portable acoustic hailing speaker (similar in concept to the LRAD) at a gathering of audio enthusiasts in northern Indiana over the past weekend. It uses four 2"-exit, 200W compression drivers with 4" voice coils, fabric-reinforced phenolic diaphragms, and big 6"-diameter neodymium magnet assemblies, mounted to 4 plastic horns with 400hz flare cutoff frequency in a prototype MDF cabinet. Sensitivity for this system is about 125dB at 2.8V/1meter with a 2-ohm impedance. Power was supplied by an amplifier that can deliver 125W into 2 ohms, powered by a sealed lead-acid battery. Signal was fed from an iPhone 6 running the HyperSpike player app. I was clipping the amp somewhat, but the overall clarity and perceived sound level was reported to be very good at a distance of 500 feet away. I expect to be able to use a 3000W RMS automotive amp and 12V car battery to drive this system to full power - I just haven't bought those yet.
In the video, you see a roadway that disappears under some trees in the distance; I am standing just in front of those trees beside a white car, at a distance of 500 feet to where the video was taken.