A few clarifications.
Grenades and bombs give a loud bang, but the way they damage stuff is not by sound. The shockwaves are from gases expanding violently, not from the sound of the explosion. If you want a blast, you want explosives, not sounds.
Sound weapons do exist and are used by armed forces and law enforcement. The technology most popular nowadays has existed since at least 2003 and is called LRAD. The sound "cannon" looks like this:
Source: the wiki I linked above.
It's the drum shaped thing that the guy in the picture is holding.
This doesn't "blast". It is used in two modes: it can either make a sound so loud you can hear it from three kilometers away (that's almost two miles, about 9,800 ft), or in crowd control mode you can just use it to cause discomfort to a lot of people that are in front of it. According to this article it can cause pain at 20 meters, and even hearing loss.
Of course, since you are going for the kill, you can start with this technology and fiddle with it to come up with something lethal. Take a page from nature too.
Sperm Whales are the loudest creatures on Earth. Depending on your sources, they can reach up to 230 decibels with their natural sonar. Some biologists suggest that their loud sound is weaponized in order to stun their prey, though last I checked there was no consensus on this. However, there is anecdotal evidence that a sperm whale's clicks can and will cause bodily harm on other creatures. Some people like swimming along the critters, and at least two guys have booped sperm whales on the nose.
James Nestor was being approached by an adult sperm whale and put in his hand to protect himself. He made contact, and his hand was paralyzed for four hours. He detailed his experience in his book Deep. His colleague Fabrice Schnöller also touched the nose of a calf, and similarly got his hand paralyzed. If you look at Youtube videos where they describe their experience, you see them talking about a feeling of your whole body vibrating and even heating up. Notice that while sperm whales have had violent contact with humans in the past, there has never been any report of them actually attacking humans with sound (only headbutting ships). It may either be that the whales are either incapable of causing further harm this way, or that touched Nestor and Schnöller were actually being "gentle" and could potentially have killed the divers with sound if provoked and willing.
Back to your weapon. Take the whale clicks up a notch, and you can use ultrassound to cook your victim from the inside. But you will probably need a sperm whale head sized speaker.