Sound Cannons - Look out

Toronto police reported that they had purchased several 'Sound Cannons' to use for crowd dispersal at the G20 summit here in Toronto. These canons are capable of producing (according to the manufacturer's specs) 152dB SPL at a distance of 1 metre. That is certainly beyond the threshold of pain (~120-130dB SPL) and can cause permanant hearing damage. The inverse sqaure law predicts that the SPL will drop by 6dB per doubling of distance (although this does not take reflections/reverberation into consideration). So if it produces 152 dB SPS at 1 metre, it will produce 146 dB SPL at 2 metres, 140 at 4metres, 134 at 8 metres, 126 at 16 metres and 120 at 32 metres. So even at 100 feet away (roughly 32 metres), it's pretty darn loud and will certaibly be above the pain threshold for at least a portion of the population. Bottom line is: I would advise people to keep their distance (and the bigger the distance, the better!)