The HoloLens's visuals are justifiably getting most of the pre-launch hype, but sound plays just as important of a role in creating immersion in your mixed-reality.
The effect could be as simple as hearing the sound of a spray can hissing when you change the color on one of your models in HoloStudio. Or, you know, ducking that object being hurled your way from behind.
The headset can play sound in 360 degrees, so you can hear holograms that aren't in your field of vision. The holograms will emit sound based on their position, as well as their depth—a hologram that's "further" away will be quieter than one that's nearer to you.
All you have to do is assign sounds to your holograms, and HoloLens will be able to figure out the rest itself.