Ultrasonic fat burners don't melt anything, I don't expect that a bunch of sound energy would transform into thermal energy without serious losses. I think the proposed timescale is unbelievably optimistic. But even with a more realistic 1-10 seconds until serious damage, we still have to place the seal on the Dragon and then activate it, a difficult prospect.
Remember that Jiraiya didn't get farther than 175 dB, I am not confident of Hazou's ability to get even that far, especially with our terrible Calligraphy. Going even further would be extremely hard, since we won't have examples to work from.
We have a system that probably works better all ready to deploy right now. I don't this is worth the extremely significant time investment to develop the seal without testing implosion seals first. If we get nowhere with that, maybe we can try this.
Fat burners create cavitation, which kills the adipose cells by rupturing their membranes. As for sound to heat power, all forms of energy decay to heat with 100% efficiency. As the transmission losses are 1E-3, once it is on the meat, most of the power stays there, then goes to heat.
Let's say no seal research on this, so 175 dB, which is 5E4 W. Half of that, then take away 3 orders of magnitude from transmission losses, then halve it for the hemisphere, we have 25 W per seal. Now, plaster a 20 by 20 m wall with seals, which gives 3600 seals at 9 seals per m2. So 9E4 W. Then the parabolic dome reflector in front focuses that down to 1 m2 because it is not perfect, also maybe we lose 1 order of magnitude because of the geometry. That results in 9 kW/m2 of sound at focal point. From non-coherent sources, so a pretty broad spectrum will result. High frequencies for cavitation, low frequencies for blending, mids for dubstep.
Even without cavitation and organ bursting, the heat from this can get 2 Kg of water to boiling temp in one second. On humans, you only need to warm the heart a couple degrees to cause a heartstroke.
The power level near the seals should be survivable by normal nin, as long as they have hearing protection.
It also can be shot as many times as needed, unlike doing the same with implosion seals.
If the soundblerizer is destroyed by the dragons, the massive seal failure will be interesting, and maybe marks them for the Watchers.
Want more power? Layer banshees on top of each other.
Want directionality? Use a water ninjutsu to connect the focal point with the target (and a disposable ninja depending on jutsu).
Do not want to carve? Layer seals on even floor, use air dome as hemispherical lens (requires some testing). Air dome works as lens? Create invisible 3D soundblerizer maze.
Y'know? When a storage seal fails and doesn't dump its contents it's not like they disappear. They're still floating out there in a frozen bubble universe. That must have happened a great deal of times over the centuries. It shouldn't be too difficult to create a seal which links up to the most metaphysically close bubble universe and dumps them out.
I fully admit that this is just the urge to see Hazou's office door with a "Gon fishin'" card on it.
First thing that comes to mind is most of it must be from failed seal research, so expect a lot of berries and the occasional researcher to come out of it. Then this being MfD, obviously some of the local wildlife evolved to feed on these pockets. First on the food, then on the actual spatial anomalies. Working storage seals are not more metaphysically stable, their jagged 13-D edges make them difficult to feed on. Pity the pure world is (was) so smooth and chewy.
