Sound absorption vs sound blocking
Often, when we find a space to be too noisy we say it needs “soundproofing”. But what does that mean?
When talking about solutions to noise, it’s essential to first understand the problem in order to be able to apply the appropriate solution. Sound absorption and sound blocking are often mixed up, used as synonyms even, when in reality they are two very different things.
Sound blocking has to do with isolating a space from exterior noises, while sound absorption has to do with improving the acoustic comfort of the space. Sound blocking requires very dense and heavy materials to block sound, sound absorption requires soft and porous ones to absorb it.
Street construction noise perturbing your quiet time at home is one thing.
Having to shout over the table to talk to your date at a busy restaurant is another.
Both situations illustrate a noise issue, but they require two very different solutions.
Let’s take a look at them one at a time.
Sound blocking
What is sound blocking?
Sound blocking refers to creating an impenetrable barrier for sound.
This means isolating a space from exterior noises, as well as preventing sounds generated in that space from escaping to the exterior or neighboring spaces.
When is sound blocking necessary?
Sound blocking is necessary whenever there’s a sound that shouldn’t be there, at all.
If you live in an apartment building and can hear your neighbor’s TV, that’s a situation that requires sound-blocking measures.
If you want to open a nightclub and don’t want the neighbors to call the police on you, that’s a situation that requires sound-blocking measures.
If you are installing a noisy machine that’s going to run for extended periods of time, such as an AC or a powerful refrigerator, that’s a situation that requires sound-blocking measures.
If in an ideal world, a sound shouldn’t even exist, that’s probably a good candidate for noise-blocking measures.
Sound blocking materials
What materials are good sound-blocking materials?
We’ve already talked about how sound works and how it propagates. In a nutshell, energy makes materials vibrate, thus creating a sound. Air is a material that we set to vibrate in a certain way thanks to the energy coming from our lungs and vocal cords, that’s how we speak. Water can also vibrate, and that’s how many marine animals communicate, etc.
Any material has the potential to vibrate and therefore transmit sound. However, vibrations are nothing less than a repetitive motion, and some materials are harder than others to set into motion.
As a rule of thumb, the heavier and denser a material, the harder it will be to set in motion, and therefore the better it will be at sound-blocking.
Picture a space divided by a simple curtain and the same space divided by a solid concrete wall. Intuitively we know that the concrete wall will do a much better job at blocking sound, right? Well, now we know that’s because concrete is way heavier and denser than the fabric of a curtain.
So, in the context of construction, the best way to block sound is by using heavy construction materials from the very beginning. Brick, concrete, stone, etc.
This is also why recording studio doors look very much as if they belonged to a security vault. These doors are incredibly heavy and usually loaded with heavy metals to help block sound from traveling between rooms.
If you need to improve the sound-blocking properties of a space that’s already built, mass-loaded vinyls are probably your best option. Mass-loaded acoustic vinyls are materials that contain particles or layers of mass that absorb sound waves. The mass added to the material increases its total weight, which makes it more effective at blocking sound. They are often used in walls, ceilings, and other structures to reduce noise transfer from one area to another.
Sound absorption
What is sound absorption?
Sound absorption refers to the reduction of reflected sound waves within a space, also known as echo or reverberation.
Think about sound absorption as selfish soundproofing techniques. In this case, we don’t care if the noise travels to the next room, or if it bothers the neighbors. The thing sound absorption will help us achieve instead is a higher acoustic quality and comfort within the space where the sounds are produced.
When is sound absorption necessary?
Sound absorption is necessary whenever the quality of the sound in a room is important.
If you are setting up a home theater with a powerful sound system, that’s a situation that could benefit from sound absorption techniques.
If you want to create a home recording studio, that’s a situation that could benefit from sound absorption techniques.
If you are opening a restaurant and want your guests to be able to talk to one another without having to shout over dinner, that’s a situation that could benefit from sound absorption techniques.
Reducing the echo and reverberations of a room might not seem very important, something reserved for sound freaks. But the truth is any space treated with sound absorption solutions will immediately become a lot more comfortable to be in. Your brain will not have to actively filter out all the irrelevant noise and you will feel better, more relaxed, and will have an easier time focusing on things. This is why properly soundproofing corporate and work-from-home offices is key to improving performance.
Sound absorbing materials
Sound-absorbing materials are literally the opposite to sound blocking ones. Sound-absorbing materials are light and porous.
Foam, rubber or textiles are excellent at absorbing sound.
Imagine throwing a ball (which represents the energy of a sound) against a wall. If the wall was made of pure concrete the ball would bounce right back at you. That would mean the sound was blocked, as discussed earlier, but also a huge echo/reverberation was thrown right back at you. Now imagine that wall was made of foam. The ball would fall straight to the floor after hitting the wall. The wall will be completely deformed (bad sound blocking), but the ball will not bounce back at you, (great sound absorption).
The only problem with soft, sound-absorbing materials, is that they are hard to incorporate into spaces. Let’s face it, a wall made of rubber isn’t very practical, and you cannot have foam shelves or textile windows…
Soft materials are delicate, and also harder to clean and maintain than, let’s say, glass or metal.
That’s why acoustic panels are such a popular solution, especially when designing offices or retail spaces. Acoustic panels are standalone pieces that incorporate a lot of these soft materials (also combined with some smart geometry that also helps reduce echo) in a manageable block, easy to install, clean and most of the time, even decorative.
Softwoods can also contribute to sound absorption. They might not be as light as foam, but they are fairly light compared to other construction materials, and you can use them on floors, walls and furniture. That’s why most auditoriums have their walls paneled in wood.
Conclusion
So, to recap. Both sound-blocking and sound absorption are important aspects of soundproofing, but they refer to two very different desired outcomes.
Sound-blocking refers to literally blocking sounds from flowing from one space into another, and requires dense and heavy materials such as concrete, stone, heavy metals, etc.
Sound-absorbing on the other hand refers to improving the sound properties of a space by reducing echo and reverberations, and requires light and airy materials such as foam, rubber, textiles, etc.
Trying to achieve either one with the wrong materials will be like trying to solve an algebra equation by chewing bubblegum. So it’s imperative to first define what we want to achieve before we can design a successful soundproofing strategy.
My personal opinion is that, in most cases, the best soundproofing projects are the ones that consider both sides of the equation. Because we want to be able to listen to our new home theater loud and clear, with no echoes or interferences, but also our neighbor doesn’t need to know every time we decide to watch an action movie!