o-o
What is sound irl? Sound is just oscillation of air. That is pretty much it lol, there are several ways to make sound, and almost anything someone does creates a sound, even if just a little. Sound is everywhere but the only place sound can't be in is a Vacuum, because sound needs a medium to travel through. Places like space cant have sound because there isn't a gas, liquid, or solid to have it pass through, it is just nothingness. Kind of illogical for it to happen anyway.
Sound in the naruto context? Sound is created by just oscillated air pressure. A requirement is that wind and lightning must be mastered, which I would assume because of lightning's vibrating nature and wind being actual air currents, lightning changes the nature of the air currents and makes it into sound. It makes it operate in the form of Waves instead of currents. Canon, must people used a device to amplify sound, but in the RP, it's just chakra conversion isn't it?