How to Ventilate a Sealed Room
Soffit Mufflers and Dead Vents
It’s unfortunately a very common scenario to build a soundproof room, with massive walls and ceiling, only to forget about the ventilation. You are going to need to seal the room tight to prevent leaks, yet you’ll need to get air in and out of the room. You have to build ventilation mufflers to drop the noise level in the ventilation before it exits into the main HVAC system.
One word of caution: There is a common internet myth that flex duct will solve all of the issues with the noise. People feel great about cutting large 6″ diameter holes in the now soundproofed ceiling, exposing the original framing behind the layers of ceiling drywall. They don’t worry because that 6″ diameter hole has insulated flex duct in the joist cavities. And they “have incorporated a bend or two” in the flex, so all sound problems are taken care of. Nothing could be further from the truth.
The flex duct does not have nearly enough absorptive material to deal with sound waves. Sound will simply blast through flex duct and keep traveling to other parts of the building. There is a great deal of false soundproofing hope associated with this method. Don’t get me wrong. Flex duct has a distinct role in sound isolated vent designs, however, the flex must be combined with more standard insulation to create a significant muffler.
These ducts fit nicely in a room’s soffit.
Yet there are times when a soffit muffler isn’t practical. In these cases, a Dead Vent might be more appropriate:
The Dead Vent can be installed outside of the sound room, perhaps in a closet or utility room. Between the Soffit Muffler and the Dead Vent, most ventilation isolation scenarios can be accommodated.
We have manuals available to discuss this in greater detail: Soundproofing Manuals (SIM)