Thanks for your reply.
What about as a trigger to detonate a (crude) bomb.
Ideally I'm trying to think of some sort of scenario wherein the playing of a particular sound could lead to the detonation of a nearby explosive; maybe not directly, as suggested before (in that the frequency itself ignites the explosive), but as a trigger.
I'm wondering if it would be possible, without the physics of it being overly-complicated; the technology involved would have to be relatively simple.
Well it does remind me of a schoolboy prank one of my friends told me of, when we studied chemistry together at Oxford. In their final week at school, he and some schoolfriends managed to make either picric acid (trinitrophenol) or nitrogen tri-iodide (I forget which it was) and paint it onto the felt hammer of one of the piano keys in the school hall. The idea was that the school song would be sung at the final assembly and they had found that in the bridging passage between the two verses, there was one key that would struck only during this passage. So they soaked this one hammer felt in the explosive.
He told me it worked a treat. Everyone sang as usual and then, during the bridging passage, there was a loud bang, amplified by the sound board of the piano, accompanied by an emergence of a cloud of dust from within, followed by a nervous silence, after which the pianist hesitantly resumed.
Nitrogen tri-iodide is sensitive enough to be set off by sound I think, but it would not be sensitive to a particular frequency. I cannot think of any explosive that would be that selective.
I'm sure an electronics engineer could build a circuit that would produce a signal only if one specific frequency of sound were detected. That signal could be used to activate an electrically triggered detonator.