Air vents are usually placed above doors to let rising hot air out from the room and the fresh breeze in. With the air the vents let in and out, comes a lot of noise. And if you soundproof the room (to minimize the noise) you might notice insufficient ventilation. It occurs because, sometimes, the vents get covered or blocked by the soundproofing panels.
Every soundproof room needs proper ventilation. To overcome this dilemma all you need to do is to change the current vents (or build new ones if there aren’t any) into sound blocking ventilation ducts. This could be done if you either:
- Use a soffit muffle
- Build a new dead vent for the space
You can create a fairly efficient ventilation system yourself with a little DIY knowledge and help.
Note the kind of fan you already have as small and axial fans tend to make more noise than large or centrifugal fans.
What is Soundproofed Ventilation?
Soundproofed ventilation refers to a situation where you soundproof all means of ventilation in a room. Meaning, your room is completely soundproof but still lets an adequate amount of fresh air inside.
Rooms that require a high level of soundproofing still need ventilation to maintain a healthy environment for the inhabitants. Ventilation is necessary for any type of room, be it a fully noise-free recording studio or your bedroom. It’s not an option to skip air vents or HVAC systems.
Oftentimes, people tend to either completely block or cover the vents or fill the vent with a sealant. This means all gaps for air to come in or go out get blocked. This might be a great way to reduce airborne noise in a room, but it is not recommended to block ventilation altogether!
Generally, HVAC systems make a certain degree of noise when they are in use. These systems use open, large pipes that actively enhance the “bouncing” of sound waves which, in turn, cause echoes and reverberations. But that certain level might not be acceptable for places that require a perfectly balanced sonic environment.
On the room-facing end of these pipes, most of the noise you hear is from the fan. When you soundproof (block) these vents, the poor airflow causes more noise in the whole system as it works to suck more air in. The velocity and pressure rise and this affects the air field surrounding the vents.
How to Ventilate a Soundproof Room?
It’s actually quite simple to ventilate an already soundproof room without any professional help (though consultation and direction always help). Here are some solutions for ventilating a fully soundproof room:
Soffit Mufflers
A soffit is the underside of an architectural structure. They are built to protect the structure from elements of nature such as moisture or mold. Soffits are sometimes also referred to as false ceilings.
Soffit mufflers, also called ventilation mufflers, are designed to reduce noise at the opening before they can get into the HVAC system and travel. You can also build it by using 6 to 8 inches of flex duct, some drywall, insulation, green glue and a silencer (if your budget allows).
You will have to put a flex duct in and run it towards the HVAC system from the vent. Then, build a small box with green glue and drywall in the cavity of the ceiling to surround the flex duct as much as you can. You may also surround the box’s walls with fiberglass insulation to increase its soundproofing ability.
This muffler basically dampens or absorbs any noisy sound waves that are passing into the room via its ventilation system.
Construct a Dead Vent
A dead vent will easily fit in with your HVAC system in walls or under the floor.
Dead vents function due to dead air space (an unventilated, airless area where air does not circulate). A dead vent lets sound enter into such dead air space, traps it, and lets it out where it cannot be heard.
You basically exchange the air of a soundproofed room with another one. Hot air rises up and is pulled through the soffit into the dead vent and cool, fresh air from the other room is pulled in. Ideally, you would need one dead vent for each supply and one dead vent for each air return.
Dead vents work best when you operate them as a separate system having their own fans. You should never connect a dead vent system to your HVAC system because doing so pours noise directly into the ductwork. Instead, you can utilize a dead vent as a buffer between the main HVAC system and the soundproofed room.
You can build it yourself with drywall, flex duct (6”), green glue, centrifugal duct fan, and some nails to put together the cavity insulation. Start by double layering the box with green glue and drywall. Cut holes on long, opposite sides for the duct to go in an “S” shape. Put the fan in the center of the box and run a flex duct through both ends to meet it. Line the box cavity with insulating fiberglass to absorb sound waves there.
Sound Baffles
A sound baffle is just a box that makes the passage of sound waves a little longer for better absorption. You can integrate sound baffles into your current HVAC system as well. The idea is to make the sound waves travel for such a long time that they get completely absorbed once they reach the soundproof room.
A vent baffle works just like a muffler on a car. This is one of the cheapest ways to ventilate a soundproof room if you have an HVAC system already in place. You can also make them yourself using insulation foam, duct fan, and some medium-density fiberboard.
Build the box from MDF, about 2’ long and 1’ wide and line it with insulation. Place the duct fan on a mount in the middle and run a flex duct with multiple 90-degree turns in it. The turns and angles bounce sound waves in various directions and dissipate as much energy before they reach the endpoint.
Conclusion
Air vents are commonly ignored during the whole process of soundproofing a room. It’s also a common misconception that soundproof rooms need to be airtight. They don’t!
Instead of blocking, soundproofing the existing ventilation system is more effective. Use soffit mufflers, dead vents or sound baffles to allow fresh air in without compromising on the sound quality of the room.
If you have a fully functioning HVAC system in place, your best pick would be a soffit muffler as it lowers the decibels in vents before it exits into the main HVAC system.