How To Block Sound Between Rooms With Effective Soundproofing

Jeff Autor’s Home Theater using absorptive SoundSued Acoustic Wall Panels.

Perhaps the most asked question I receive from customers is how to block sound between rooms. Whether for a home theater, podcasting studio, conference room in the office, or even just a bathroom wall to hide the sounds of the toilet, room-to-room sounds can be annoying at best and disturbing to important activities at worst.

Recently, a customer called asking about how he could block sound at his company’s new office. The company had recently purchased new office space and spent a great amount of effort to renovate it to be effective at promoting workplace well-being and thus efficiency. To do this, the core of the office was a great open room where the bulk of the employees work. Surrounding this open space, executive offices and conference rooms were placed for more privacy, or so my customer thought. It looked private, but once they were up and running, he quickly realized that all of the chatter and sounds from the open area workplace on the other side of the conference room wall was penetrating, creating a constant thrum of sound that he said customers could even hear through Zoom calls in the conference room!

He was disappointed as the renovation was brand new and while it looked good, the sound was a problem. I told him not to worry, as wall soundproofing is extremely effective and can be accomplished readily. With a few adjustments made by the renovation team, the conference rooms and, subsequently, the executive offices were soundproofed and allowed for their most important decisions to be made in peace.

In this article, I’ll discuss the concept of soundproofing and explain how we use acoustic materials to properly soundproof walls no matter the application.

Understanding The Concept Of Soundproofing

When we discuss improving acoustics in a space, there are two key but distinct concepts: soundproofing and sound absorption. Often confused, they are quite different, and I make sure my customers understand this from the get-go so they have the right foundation to accomplish their goals.

Here, we’ll be talking about soundproofing, also known as sound blocking. I tend to prefer this phrase because it’s more descriptive: what we’re trying to accomplish with soundproofing is using material to block sounds. In the case of walls and sound transferring, we want to introduce materials in an assembly so that by the time it passes through the energy of the sound wave is so diminished that it either cannot be heard or has been reduced to barely perceptible.

The key to blocking sound is having the right material placed in the right way within the wall. You might think walls are solid, and many of them are, especially if made of concrete like in some commercial buildings, but sound is tricky and can readily pass through materials we cannot.

Take for instance a normal wall, constructed of studs and drywall. Theoretically, we might be able to punch through the wall with significant effort and claw through the drywall and insulation and in between the studs to the other side, but that would be ridiculous! For all intents and purposes, we cannot just pass through walls. That said, sound has no problem passing through typical drywall, so we need to beef the wall assembly up to absorb the energy from the sound wave before it can enter the space we want soundproofed.

How We Soundproof: Mass, Density, And Decoupling

When thinking about materials to block sound, we have to think about density, mass, and a concept called decoupling.

Mass And Density Of Materials

To explain the importance of mass and density in soundproofing, I like to use an analogy involving arrows. If you imagine a soundwave is an arrow flying towards you, your best chance of blocking it is to put something in between you and the arrow – a shield. If you chose a t-shirt for a shield, you’re in big trouble. If you instead chose a shield of wood, the arrow will be blocked, even if the arrowhead makes it through the wood a bit.

Thinking about this with sound, the denser wood shield blocked more of the arrow, but some of it still came through. Finally, if you think about utilizing a shield of concrete, that arrow is not penetrating at all.

The mass and density of the concrete effectively absorbed all of the energy of the incoming arrow, and that’s exactly what we want to do to block sound by selecting dense materials of more mass to take away the sound waves energy.

Decoupling

Sound waves are complex in how they travel, and part of their sound comes from vibrational energy. When a sound hits a wall, its energy is imparted into the material and radiates through all adjoining material until it’s free to move through the air on the other side. To solve this problem, we want to decouple materials within the wall so that when vibrational sound energy hits a gap, its energy levels drop off significantly before hitting material on the other side of the space.

To conceptualize this, think about when you knock on a door. The whole point of knocking is to alert someone on the other side that you are waiting at the door. Your knuckles knocking on the wood impart vibrational sound energy that travels through the door material to the other side and then travels through the air as sound. Now consider that there was a piece of wood hanging in front of the door for you to knock on with an air gap between it and the door.

If you knocked on that piece of wood, your knock would not be heard inside – why? Because the piece of wood is not connected to the door and there exists an air gap between the two, what we call decoupled, the impact energy drops substantially and cannot pass into the door, effectively soundproofing the sound you made knocking.

Merging these two concepts – dense, high mass materials decoupled within the wall assembly – is how we effectively block sound between rooms.

How To Block Sound Between Rooms With Modern Acoustic Materials And Techniques

To effectively block sound between rooms, we need to look at all of the components: walls, ceilings, floors, and any openings, such as windows and doors. Depending on your circumstances, you may not have to soundproof all of these, but you do need to verify and not expect just because you took care of the walls that that will be enough.

Soundproofing Walls

My favorite method to block sound between rooms is to employ a trio of products in combination to create a wall assembly that is highly effective at removing sound energy as it passes from one side to the other.

Let’s begin by thinking about our standard wall assembly: drywall, studs, and insulation within the stud cavities. This assembly is not great at soundproofing, so we are going to add mass via specialized acoustic materials and decouple the assembly to make it capable of blocking sounds.