Living in an apartment building means you’re closer to your neighbors than if you lived in a house. While soundproofing helps keep noise from passing through the walls, you might find that you hear voices through the vents as if they were in the same room.
Hearing voices through vents is usually a result of poor construction where short and straight ducts connect rooms. Soundproofing methods can be used to reduce sound traveling through vents, but there are a few things to keep in mind when using soundproofing methods.
This article will focus on this phenomenon of sound traveling through vents and the different ways you can remedy the situation. Some of the solutions are simple enough that even non-DIYers can do them, so it’s certainly worth giving them a try.
You hear voices through vents because sound travels well via the air coming through the vents. This phenomenon is more prominent in houses where ducts are made of solid metal and between rooms where the ducts do not make any turns.
Note that sound is essentially vibrating energy passing through a medium. In this case, it’s influenced by the air in the ducts and the structure of the ducts themselves. You’re more likely to notice this phenomenon in houses with a forced-air HVAC system than in a building because the ductwork in larger buildings is more convoluted.
When air travels through a duct that goes straight from one room to another in any direction, it can carry sound very clearly. Think of it like holding a pipe towards another person’s ear and whispering into it: They’ll hear as if you whispered directly into their ear and not through a long pipe.
Of course, the longer the distance that sound needs to travel, the more muted the sounds become. As such, rooms directly above each other or sharing a wall tend to transfer sound between the rooms if the air ducts aren’t turning drastically at any point between the two rooms.
Generally speaking, a straight duct that’s shorter will easily carry sound. On the other hand, a longer duct with a few bends or curves will dampen sound to some degree. Most HVAC systems follow this principle, so they usually have many long pipes installed with several right-angled turns.
How to Stop Sound From Traveling Through Air Vents
Several methods are used to stop air from carrying sound through vents. If you already notice that you can hear full conversations through the air vents, don’t worry: You don’t have to put up with it.
Here are strategies you can use to minimize sound coming through your air vents (if not block it entirely).
A sound maze is by far my favorite way to reduce sound traveling through air vents. Generally, this is a DIY project most people can handle and is pretty affordable. Air vent sound mazes are highly effective at reducing noise, so you won’t hear voices through vents if you install them.
Here’s a simple step-by-step procedure for creating an air vent sound maze:
- Remove your air vent cover.
- Measure the length and width of your air vent.
- Cut four plywood sheets the same size as your air vent.
- Scale down the plywood sheets so they’re around 30% smaller than your air vent. For example, if your air vent is 9″ x 9″, your plywood sheets should be around 2.7″ x 2.7″. Scaling down doesn’t need to be exact, but the plywood sheets should fit securely at least.
- Using green glue, stick the first plywood sheet deep inside your vent on one side. Make sure there’s enough space for the other three sheets.
- Stick the next three plywood sheets on alternating sides. You should have two sheets on the left and two on the right.
- Adjust the sheets as needed.
- Wait for the adhesive to dry.
- Close up your vent.
As you can imagine, sound waves would need to navigate in a zigzag motion to go through the plywood sheets you have placed. The sheets act as an obstruction, significantly dampening the sound. This method ensures that air flows freely through your vent since the plywood sheets are smaller than the vent.
However, sound waves will bump into the plywood sheets and reflect, resulting in energy loss before the sound waves reach the vent. There’s no need to use reflective materials under this method.
You might be surprised to know that you can line the interior of the ductwork in your home with sound-absorbing materials. The lining acts like a sponge that dampens the sound as it travels through. While this solution doesn’t entirely remove noise, it can make rooms much quieter.
Sound absorbing duct liners are a relatively cheap solution to insulate sound traveling through vents. I highly recommend this SmartSHIELD insulation Roll on Amazon. It’s an excellent material for dampening sound, and you can use it to line all the ductwork in your home.
Now that you’ve covered the interior of the ductwork in your home, you may want to consider covering the vents themselves. This solution works best if the sound issue is restricted to only one or two rooms in your home.
Keep in mind that if you use vent covers, you effectively block airflow in the room. Blocked airflow may cause temperature changes and even be a fire hazard in some cases. (I’ll explain these issues in more detail later.)
Several options are available for vent covers, including:
- Soundproof Curtains: This is perfect if you only need to temporarily cover vents for sound insulation. These curtains are made of dense material that absorbs and dampens sound without disrupting airflow. I particularly like these NICETOWN Noise Reducing Blackout Drapes on Amazon. They come in different colors that can suit your interior design and personal preferences.
- Magnetic Vent Covers: These are vent covers designed to easily stick to air vents. They can cover your vents without having to use adhesive to stick them in place. You can also conveniently remove them whenever you need to increase airflow in a room.
When all else fails, you can try blocking the vent entirely using drywall. It’s a relatively easy DIY project, but you should be sure this is the best option for you. Covering an air vent means blocking the room’s airflow, which may pose a few safety risks.
If you decide to cover your air vent using drywall, there should be another source of airflow in the room, such as a window. Drywall is fire-resistant, so there should be at least one other source of ventilation in case of a fire.
Foam sealant is another option you could look into if you don’t mind blocking your air vent permanently. Typically, you can buy foam sealant in a pressurized canister. Once the sealant is exposed to air, it expands to fill as much space as possible.
Spray the interior of your air vent generously using foam sealant. The foam will expand to fill the entire vent. You can add more if needed, but generally, one application is enough.
Earlier in this article, I discussed how straight ducts carry sound much better. Because your desired outcome is noise reduction, you may want to try installing flexible ductwork that doesn’t carry sound as well as straight ducts. Flexible ducts have many curves because they’re bendy, and the walls of the ducts act as obstructions to traveling sound waves.
In other words, the sound waves would reflect off the curved walls of flexible ducts, and they’ll lose energy along the way before reaching the vent. The result is a significant reduction in sound from your air vents. Luckily, most houses already have flexible ducts installed.
It’s worth noting, however, that this solution can be quite expensive. It’s always better to install flexible ductwork from the start. If the ductwork in your home isn’t flexible, you can cut down on costs by only replacing ductwork between some rooms instead of upgrading the entire system.
Blocking an air vent may solve the issue of sound traveling through ductwork, but it can lead to other undesirable effects as well. It’s important to keep these effects in mind before soundproofing your vents using any of the methods mentioned above.
The following are common effects of blocking an air vent. Before making any permanent changes, you should look over the different problems that can arise from blocked air vents. That way, you’ll know how to work around them if necessary.
In most modern homes, the ductwork is part of the installed HVAC system. Generally, the HVAC system blows cold, humid air into a room to bring down the temperature. If you block some of the air vents (even partially), the HVAC system will still function, but the humid air will have no place to go.
As the humid air bumps against any air vent obstructions you’ve placed, the water vapor condenses near the vents. This accumulation of water could potentially lead to damp forming in your walls — a dangerous problem with potentially serious health consequences.
Related: Does Opening Windows Reduce Damp?
It should go without saying, but blocking an air vent means blocking the airflow. The reduced airflow will be very noticeable whether your air ducts are for ventilation or part of an HVAC system. You might notice rooms becoming stuffier, and the temperature in different rooms might increase or decrease depending on where you live.
Some people find that staying in a room with reduced airflow can feel suffocating, especially those who suffer from claustrophobia.
The reduced airflow is one of the main reasons people opt to use a sound maze instead of blocking air vents completely. In some cases (such as when building a recording studio), blocking the air vent is still a preferred solution despite reduced airflow.
When your air vents are partially blocked, the HVAC system needs to push out more air through the vents to achieve the desired temperature. The cold air that travels through a sound maze or goes through other soundproofing obstructions heats up slightly, so more cold air needs to pump through the vents.
As such, the HVAC system would be spending more energy to bring down the temperature of a room when the vents are blocked. The same is true if you’re using the HVAC system to heat a room because the warm air cools down as it passes through partially blocked vents.
Not only is it inconvenient to wait longer for your room temperature to come down (or up), but the increased energy usage will inevitably lead to higher bills. Additionally, it’s bad for the environment.
As I’ve mentioned above, partially blocked vents increase the energy usage of an HVAC system. Not only that, but the increased energy usage puts a strain on the HVAC system and might even potentially damage it. Damage to your HVAC system is more likely if you completely block a vent using drywall or foam sealant because the motor will continue to pump air towards a vent for too long.
Keep in mind that a damaged HVAC system is very expensive to repair. So, I suggest trying a sound maze first because this soundproofing method doesn’t block airflow as much.
Although some sounds will inevitably travel through air vents, there are ways to ensure you don’t hear voices through vents to the point of accidentally listening in on an entire conversation. Completely soundproofing a room with air vents is technically possible, but it does have its drawbacks.
Overall, it’s better to ensure that ductwork is built in such a way as to prevent sound from traveling through it. Trying to dampen sound is much more difficult if your ductwork carries sound too well.