I have a being that does not have vocal cords, and instead, speaks to 3-dimensional beings(humans) by manipulating air to produce what sounds like human speech. What would its voice sound like?
If he's adept, he'd sound like a human on a high-quality audio system.
All sound, including speech, is the result of vibrations in the air. There is no difference between vocal cords, cone speakers, and your "manipulating air to produce sound" being because they all "manipulate air to produce sound."
So, "vocal" quality is the result of how adept the being is at manipulating the air. If he's good, he sounds like Bing Crosby. If he's not, he sounds like an early Apple II speech synthesizer.