This actually a design consideration in HVAC engineering, from what I know. There's usually a compromise between flatter ducts, which consume more energy, produ

This actually a design consideration in HVAC engineering, from what I know. There's usually a compromise between flatter ducts, which consume more energy, produce more noise but take up less vertical space, and squarer ducts, which are quieter, more efficient but take up more space. However going too far towards large, square ducts can reduce the background noise produced below the level that many office workers are used to.