Does a Brick Wall Absorb Sound?
If you’re starting a soundproofing project around the home, you might have wondered, does a brick wall absorb sound? I’ve done some research to get the facts, so here’s a quick answer:
A brick wall doesn’t absorb sound, it reflects and blocks it instead. The thickness and density of a brick wall stop sound from passing through it, but the sound waves bounce back towards the source rather than getting absorbed by the structure.
In this article, I’ll cover the difference between reflection and absorption in relation to a brick wall and I’ll cover some tips on how to improve a wall’s absorption capacity.
Also read: How to Soundproof a Brick Wall
Why Doesn’t a Brick Wall Absorb Sound?
In soundproofing terms, there’s an important distinction between absorption and blocking. While both are useful, they have different pros and cons.
Blocking is defined as the process by which a sound wave simply can’t pass through an object or structure. The sound waves hit the surface and either dissipate or reflect back towards the noise source.
Absorption is the process of sound waves being converted into another form of energy; usually heat. For this to be possible, they have to be able to enter the material or structure in the first place.
So why doesn’t a brick wall absorb sound? Simply put, it’s down to the material. Bricks are hard, rigid and dense. Materials that absorb sound usually tend to be flexible and have an open structure, such as acoustic foam.
The same is true for almost all rigid construction materials, including:
- Concrete
- Steel
- Stone
This isn’t to say that a brick wall wouldn’t play an important role in a soundproofing project. In fact, it would be a brilliant place to start because it’s mass-rich and blocks sound from passing through.
But these aren’t always useful. For example, they’re ideal qualities if you’re trying to prevent sound from entering a room, but not if you’re trying to improve the acoustics within a room.
If sound waves are prevented from passing through a structure they’ll be reflected back towards the source. This can result in echo and reverberation, which aren’t good for soundproofing projects.
Therefore, you’ll often need to modify brick walls with materials that can absorb sound waves. These range in use and effectiveness, but I’ll discuss them in more detail below.
So, in short, brick walls don’t absorb sound, they block and reflect it. However, a brick wall is still a good starting point for a soundproofing project, you just need to use dedicated materials to improve sound absorption in a space.
The Pros and Cons of Brick Walls for Soundproofing
Although I’ve covered them briefly above, it’s helpful to have a comprehensive list of the pros and cons of brick walls for soundproofing.
Pros
1. They’re massive
This doesn’t mean they’re big (although they can be), the term massive here refers to the high mass of bricks. Compared to standard construction materials such as drywall, brick walls have plenty of mass.
Mass is useful for soundproofing because it reduces the sound waves’ ability to vibrate a structure.
2. They block sound
As mentioned, brick walls effectively block sound from passing through. This is a great starting point for a soundproofing project because it means you won’t have to do as much work to improve the space.
3. They have a high STC
STC, or sound transmission class, is the rating of how well a material isolates sound. A higher STC means a material is more effective at isolating noises.
Although a rough guide, the STC of masonry can be anywhere between 44 and 55. This is a pretty good starting point for soundproofing, and can be improved further by adding other materials.
4. Easy to work with
This isn’t to say brick walls are easy to build. Rather, I mean that they’re easy to modify and improve, as brick can easily take screws and nails, and can bear a lot of weight.
Cons
1. They reflect sound
Blocking sound is a good thing, but reflecting it back into the room isn’t. Therefore you’ll need to modify a brick wall to make it as effective as possible.
2. Can be expensive to build
If you’re starting from scratch, building a brick wall can be expensive. Realistically you’ll need to hire a professional to do it, and this will take time and money. A cheaper and faster option would be to build a stud drywall and insulate it.
How to Improve Sound Absorption for Brick Walls
Luckily, it’s pretty easy to make a brick wall absorb sound. It doesn’t require much work, and you have plenty of options.
Here are my top picks.
1. Use acoustic foam
Acoustic foam is specifically designed to absorb sound. It has an open-celled structure that traps sound waves and converts them to heat energy.
Breaking up the flat surface of a wall will easily improve sound absorption and reduce echo.
You can stick with normal acoustic foam alone or combine it with bass traps to combat all frequencies.
2. Hang curtains
While this isn’t a dedicated soundproofing material, curtains are reasonably effective at absorbing sound waves.
This is because they’re everything a brick wall isn’t: soft, flexible, and fairly open. Hanging curtains in front of a brick wall will reduce its reflection properties.
The further from the wall you hang the curtains, the better a job they’ll do. A gap of 2-4” should be fine if that’s possible.
3. Put up some drywall
Drywall alone isn’t brilliant for soundproofing. However, it’s what you put behind that helps. Coat the backside of the drywall in Green Glue (Amazon link) and it’ll be much more effective.
Green Glue is a noise dampening compound that converts sound waves into heat energy. Putting a layer of it in front of brick and behind drywall will reduce the amount of noise that makes it to the brick wall.
4. Carpet and furnish the room
This is something of a cheap hack, but it definitely helps. Adding soft furnishings to the room, along with some carpet, will help absorb more sound and reduce echo.
The furniture, such as chairs and sofas, will absorb the sound waves and covering the floor with carpet or rugs will remove a large flat surface. This simply gives the sound waves one less surface to reflect off.
5. Build a room in a room
Decoupling is arguably the best way to soundproof a space. This is also referred to as a room in a room because you’re isolating the interior space from its surrounding walls.
A brick-walled room is a good starting point because it provides a good barrier, but adding another room within it will be best.
It’s quite a complicated process, so check out this video on building a soundproof room for more details.
Some Final Thoughts
Hopefully, this article has explained why a brick wall doesn’t absorb sound. Remember though, this doesn’t mean it’s useless for soundproofing. In fact, it’s quite the opposite.
You’ll just need to work with the limitations of brick to make it as effective as possible. Luckily, this is pretty easy.
I recommend deciding which option fits within your budget and planning how best to tackle the project.
