I've got one supply register in my master bedroom, it gets quite a bit of air velocity because it is only about 4 feet from the AC system in the attic. This can be quite noisy and I like my AC to run without catching my attention. I'm thinking about splitting it from 1 6" duct to 2 5" ducts and adding dampers. Any problems with this?
Not an HVAC guy, but FWIW,
at best the new ducts will reduce airspeed 30%. Maybe the perceived noise level will drop more than this.
Re: 4 feet, adding internal duct vanes may reduce noise due to air turbulence.
claims to tune the system for reduced noise, I guess much like an auto muffler is tuned to cancel out noise at some freqs.
From the Web, looks like dampers increase turbulence, but maybe I should have said, "Sounds like dampers increase turbulence."
I guess an auto A/C system almost always equals a poor ductwork design/install because the auto marketing people define the overall auto internal geometry and leave it to others to reduce the auto A/C noise level, so I'd look into auto A/C designs for solutions to problems like this.