Does Soundproofing Work Both Ways?

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I often get people coming to me with problems in their quest for a quieter life. A friend of mine recently asked: “does soundproofing work both ways?” While I was pretty sure I knew the answer, I decided to do some research to confirm.

So, does soundproofing work both ways? Proper soundproofing relies on lots of mass, which means that it’ll reduce noise pollution on both sides of the barrier. Therefore, soundproofing will mean that sound can’t enter or escape the room, benefiting people on both sides. 

While soundproofing effectively works both ways, it’s important to know that this isn’t true for all elements of acoustic management. Having a properly soundproof room should also mean you install other features, and these will usually only work one way.

Does soundproofing work both ways?

One of the biggest problems when it comes to soundproofing is dead air. This is essentially the air gap in walls, windows, or doors, and allows sound waves to resonate, which creates noise. There are a few ways to solve this problem, and combining them all will lead to a soundproof room.

• Absorption. Wall cavities can be quite large, and stuffing them with a dense material can help absorb vibrations and sound waves, which makes it harder for noise to travel through the wall. The best materials are fiberglass, wool, or cotton.
• Decoupling. This is the process of separating walls and floors. Essentially, it means isolating walls from each other so that vibrations can’t pass through.
• Damping. Reducing sound resonance helps minimize the problem in the first place. This is usually done by adding more mass to absorb the sound waves, and adding acoustic management products to redirect sound waves.
• Mass. Adding more mass to the room will help to absorb sound waves. Adding extra drywall is useful, as is a product called mass loaded vinyl (link to Amazon). This will help to decrease reverberation and resonance.

Combining these 4 principles will result in a largely soundproof room, although it’s pretty much impossible to make it completely soundproof. Things like adding mass and decoupling work both ways, as does absorption.

An important principle in soundproofing is isolating sounds from each other. In short, this means that there should be a complete barrier between the inside and outside of a room. Therefore soundproofing materials generally have to work both ways for a room to be truly soundproof.

However, this isn’t true of all acoustic management solutions. For example, using acoustic foam for damping will work better in the room because it’s about reflection of sound waves rather than absorption.

Similarly, something like acoustic foam usually has a textured side and a smooth side. Sound reflection is much more effective on the textured side because sound waves can’t bounce off it as easily, meaning they dissipate.

So, the bottom line is that almost all soundproofing methods will work both ways. Decoupling is designed to isolate the inside of a room from the outside, while adding mass helps to absorb sound waves. Just remember that not all options work the same both ways.

What’s the best option for soundproofing both ways?

While most options will soundproof both ways, some will definitely be more effective than others. If one of your main goals in your soundproofing project is to reduce noise both ways, rather than just stop noise getting out, then it can be worth knowing which options will be most helpful.

However, your ability to do this will also depend on the room next to the one you’re soundproofing. For example, you might not be able to decouple a wall if it joins onto your neighbor’s house. Knowing the best options will help you decide which is best, so read on to find out more.

Decoupling

Decoupling is one of the most useful options for any soundproofing project. Providing you add mass too, you’ll end up with a pretty good result. It can be a pretty big job, so it helps to know more about it.

In short, decoupling is the process of separating two sides of a wall to prevent vibrations from passing through them. This usually means suspending each side of drywall independently from the other, such as by separate studs.

Having each side of drywall on separate studs means vibrations travel into one stud but can’t go any further. It’s these vibrations that can resonate in the wall cavity, eventually resulting in sound.

The best type of decoupling is to build two separate stud walls, including insulation, with a small cavity between them. This will basically completely stop sound waves from passing through the wall, but can be a big and expensive job.

A second, slightly easier option is to stagger the studs. This means you only have a single cavity in the wall, which you can fill with insulation, but it won’t be as effective as a double stud wall.

 

Read staggered stud vs double wall to know how effective they are for soundproofing.

The main weakness of decoupling is that it can increase resonance at lower frequencies, particularly with bass. However, this can easily be solved by adding more mass to the structure, because vibrations won’t pass through as easily.

Similarly, decoupling a wall means you need access to both sides. While this will be fine in your own home, it might not be viable if you’re trying to block out a loud neighbor at the same time as soundproofing your own room.

Adding mass/decoupling

 

A less invasive option for soundproofing both ways is to add mass to your side of the wall. Adding mass is simply making the barrier between the two rooms thicker, which makes it harder for sound waves to pass through.

If you decide to go for this option, the only 2 products I’d recommend using are drywall and mass loaded vinyl. These are the most effective for adding mass, aside from stuffing a wall cavity with wool or fiberglass.

More than anything, adding mass basically makes it harder for the wall to vibrate, which reduces noise pollution. Adding mass on your side of the wall will both reduce noise pollution entering and escaping.

Drywall is the cheapest and most readily available product. It’s really easy to attach to your existing wall, although you’ll obviously have to work around HVAC vents and plug sockets. Providing you seal the edges with acoustic caulk, such as Green Glue (check price on Amazon), it’ll certainly make a difference.

That said, drywall will add bulk to your walls. It’s not exactly the thinnest material, so bear in mind you’ll lose space in your room. Also, it’s not even really very dense, it’s just one of the easiest things to stick up on the wall.

Mass loaded vinyl, on the other hand, is specifically designed for soundproofing. It’s limp mass, which means sound waves just dissipate against it. I’d recommend adding a layer of mass loaded vinyl and then possibly covering it with more drywall, simply because it’s not the most attractive product in the world.

Some final thoughts on soundproofing both ways

Knowing that most soundproofing options work both ways is definitely helpful for almost all soundproofing projects. After all, there are few people who’d be happy with noise either entering or escaping a soundproof room.

The most important advice I can give on this matter is to combine different options if possible. The weaknesses of an option like decoupling are mostly solved by adding mass or sound absorption options.

Similarly, while you might be happy to soundproof both ways, if you’re more concerned about sounds leaving your room, then it can help to include some acoustic management products. This is particularly useful if you’re soundproofing something like a home theater, as this probably has loud speakers.

Just remember that things like acoustic panels, which control echo and reflection, will realistically only work in the room they’re in. However, managing sound properly in this way can help with overall noise pollution, so is definitely worth considering if you’ve got a loud room.

Regardless of which options you choose, it’s useful to include some kind of damping options. Green Glue (Amazon link), for example, is a special type of compound that converts sound energy into heat energy, and really makes a big difference to a soundproofing project.

Not just that, but acoustic caulk is very useful with low-range frequencies. This makes it crucial for decoupling, as this basically solves the major flaw in this option. Even so, filling small gaps in a wall with acoustic caulk will also help with noise pollution, and this also works both ways.

Conclusion

While looking for the answer to whether soundproofing works both ways, I found that it does, but some options will be more effective than others for reducing noise transfer between rooms. What’s more, combining more than one option will always be better.

Realistically, it’ll depend entirely on why you want to soundproof both ways. If it’s just that you want to block out a noisy neighbor, then you don’t have to worry about how much sound you make, whereas soundproofing a home theater in your house will need effective sound management both ways.