The idea of destroying things by tuning to their resonant frequency is well known, and even works in some cases. However, the totality of the task at hand is more complicated than that.
The idea behind destroying something by emitting sound at its resonant frequency is to transfer energy into the system at a "resonant" frequency, which is one that the material naturally continues to oscillate at rather than bleeding the energy off into some other form like heat. Any medium that is behaving elastically (like glass) has a resonant frequency which can be calculated from its properties.
The destructive bit arises when the energy reaches a point where non-linear effects start to take effect. In the case of a glass breaking, its because bonds get broken at the region of the highest stress and that causes an avalanche like effect which destroys the material. However, this is not the only non-linear effect that can be achieved. Any system wastes energy into heat. No system is perfectly elastic. As an example, a glass that is tapped, causing it to ring, will eventually stop ringing because the energy is emitted into the air as sound vibrations. You need to put enough power into the system at that resonant frequency to reach catastrophic effects before the object under attack can bleed the energy off into heat or emit it elsewhere.
In the case of a glass, this can be done with a simple loudspeaker. The loudspeaker can generate enough power to overwhelm the attenuation of the glass and cause it to reach its breakdown point. In other cases, you may need much more power. Galoping Girdie famously collapsed because the wind was capable of causing the bridge to resonate wildly enough to break down. That took more power, though. It took a mighty 42mph sustained wind to take her down.
Modern engineered products tend to be aware of such effects and are designed to be immune to them. We have many ways to bleed off vibrational energies into heat before they become an issue. For example, you may have seen these little guys on power lines:
They're called Stockbridge dampers and they're designed to stop a catastrophic failure of the wire due to a resonance associated with the wire rolling in the wind. They are tuned just out of tune with the wire so that they couple strongly with the wire and then turn that energy into heat as they change shape. This bleeds resonant energy off of the wire so that it doesn't fail.
In theory you can still attach such a system by attacking the GCD of all of its frequencies. If you have an object that resonates at 500Hz and it is coupled to an object that's tuned to 495Hz, you can still cause the whole system to resonate at 5Hz. However, this can quickly lead one into a region of frequencies where the assumption that materials are elastic is not so valid. If you have many many coupled resonators together, their common resonant frequency might be thousandths of a hertz. As you get into those ranges, the elastic assumptions get tricky. More and more of the energy can get turned into heat by inefficiency. This is why you can't find the resonant frequency of a human and have them explode.
Well, you could, but it would involve pumping enough power into the system to overwhelm our ability to dissipate that energy as heat. At those frequencies, you might as well stop thinking in terms of loudspeakers, and start thinking in terms of hitting them with a baseball bat!
Or a sword! Swords are very good at this sort of thing!
