Context: in a scenario where batteries suddenly became extremely energy dense due to some events between the main characters, I was thinking about which electromagnetic weapons I could use, such as rail/laser/microwave guns, and it came to my mind that sound waves could also be useful to propel projectiles (since they are artificially made with electromagnetism).
Some time ago I read that if you had a strong enough source of sound (like a "super-speaker"), the sound waves would start to act like an explosion and kill whoever is unlucky enough to be around.
However, the thing is that this sound wave would have to be made in a short period of time (like a normal firearm) and incredibly strong to make a "bubble" of air behind bullets and thus propel them.
And thus, it came to my mind that maybe this impact/sound wave could be strong enough to destroy its user's eardrums. But I can't tell for sure.