The "sonic weapon"--a musical instrument that's also a machine of war--plays a minor role in The Last Protector, and a much larger role in my current work-in-progress, The End of the Song. So I've been doing research into the whole idea of instruments as weapons, and made some interesting and surprising discoveries.
The most famous "instrument of war" (there's even a video series with that title) is the bagpipe. It has quite a reputation--there are stories of pipers leading the Scots into battle, only to have the enemy turn tail and run at the first sound of the pipes. To my disappointment (since I play the pipes myself), these yarns seem to be little more than legend. In truth, the Scots fought mostly among themselves and against the English, both of whom were already familiar with the sound of the pipes and therefore not very likely to find it frightening. Worse, the pipes suffer from the "inverse-square-law" problem: because the sound radiates in all directions, its intensity drops off very rapidly with distance. What's deafening at ten feet is pleasantly melodious at twenty and almost lost in the background noise at a hundred.
So where did the legend of the pipes as psychological weapon come from? Part of it could be association. The Scots had earned a reputation as formidable warriors, and the sound of the pipes meant the Scottish fighters were close behind. It's not the sound itself that's terrifying; it's what the enemy knew was coming along with the pipers. It's also possible that on one or two occasions during the imperial period, some native peoples (who'd never before heard the pipes) actually were startled by this unfamiliar shriek and fled. By the time the people learned that the sound of the pipes couldn't hurt them, they'd also learned to fear the bullets and cannon that came with the pipes. Thus are legends born.
While the bagpipe's reputation as a terrifying sonic weapon seems largely myth, modern technology is creating real sound weapons. The US military has this thing called an "LRAD" (Long Range Acoustic Device, which strikes me as one of the most unimaginative names ever), which they've supposedly used in Iraq. It's supposed to be a non-lethal crowd-control device, making a sound that drives potential rioters to disperse. The Pittsburgh police used one of these during the G20 protests last month, though the results were mixed (Jon Stewart quipped that the anarchists are probably using the LRAD's sound as their ring tone by now).
While the LRAD appears pretty crude (it just emits a loud and unpleasant noise that seems to make people move away), it does display some important advances over the bagpipe. It's a lot louder, and it focuses its sound in a narrow beam, so it should have a much greater range than the bagpipe.
So, as I work on The End of the Song, in which both bagpipes and a more advanced "sonic weapon" play important roles, I'm spending a lot of time thinking about where this kind of technology might go, what might happen if it fell into the wrong hands, and how it might be countered. Stay tuned...