Soundproofing a Wall: Methods That Actually Work

Quick answer: To soundproof a wall you pull four levers: add mass (extra drywall or a mass loaded vinyl barrier), decouple the two sides so vibration cannot travel straight through the studs (isolation clips and channel, or a double stud wall), add damping between layers (a viscoelastic compound like Green Glue), and seal every gap and penetration. A standard wall sits around STC 33. A well-built soundproof assembly can reach the STC 50s or 60s, the difference between hearing a neighbor clearly and barely hearing them at all.

Soundproofing is a powerful tool to make any space more peaceful so that the activity within can be uninterrupted. For most all sounds, their main access point to a space is through the walls, so walls are typically our primary focus when it comes to soundproofing.

In this article, I will describe the concept of soundproofing and how we take this understanding and apply it through acoustic materials to walls to dramatically reduce if not outright eliminate sound transmission.

Soundproofing is one of the two core concepts in acoustics, alongside sound absorption. While they sound similar, they are in fact distinct and I like to make sure my customers know the difference.

In short:

Soundproofing, also known as sound blocking, blocks sound from transmission between materials, such as a wall.

Sound absorption, also known as sound control, utilizes materials to remove unwanted aspects of sound in a space and make it sound better.

Now that the distinction is clear, let’s focus on soundproofing and how we apply this concept to walls. I prefer to use the term sound blocking because I think it makes it very clear what we’re trying to achieve. To be even more clear, I liken soundproofing to blocking an arrow with a shield. If the shield is a t-shirt, that isn’t going to block anything! The arrow will pass right through. If your shield is made of wood, however, the arrowhead might make it through, but the shield will stop most of it. If the shield is made of concrete (and you can lift it!) that arrow isn’t penetrating at all.

This is exactly how soundproofing works. If we want to stop sound from penetrating a wall, then we need to add mass to create a shield dense enough to block it.

Blocking sound requires the complete area to be reinforced or a sealed enclosure around the sound source, as it takes a system of materials to construct a soundproof wall.

Soundproofing has a number attached to it, and using it takes the guesswork out of this whole topic. Sound Transmission Class (STC) rates how well an assembly blocks airborne sound. A few reference points: at STC 35 loud speech is audible but not intelligible, at STC 50 loud speech is barely heard and is the common building-code minimum for shared walls, and at STC 60 or above most sound, including music and bass, is well controlled. The lower the frequency you are fighting, the higher the number you need.

Here is roughly what each step buys you. A standard insulated stud wall with one layer of drywall per side sits around STC 33 to 39. Adding a second layer of drywall lifts it a few points. Bonding that layer with a damping compound like Green Glue pushes a treated wall into the mid 40s to low 50s. Decoupling the wall with isolation clips and channel, or building a double or staggered stud wall, reaches the mid 50s to low 60s. These gains do not simply add up, and lab numbers run higher than real-world results, so treat them as direction rather than promises.

Every effective wall treatment pulls one or more of four levers. The strongest assemblies combine all four, which is exactly what the build described below does.

Heavier, denser walls block more sound. You add mass with extra layers of drywall or a mass loaded vinyl barrier. Mass is the simplest lever to pull and works best against higher-frequency noise.

When both faces of a wall are tied to the same studs, vibration travels straight through. Isolation clips and channel, or a second independent stud wall, break that path and deliver the biggest gains, especially at low frequencies.

A viscoelastic layer such as Green Glue sandwiched between two boards converts sound energy into a tiny amount of heat, taming the resonance that mass alone leaves behind.

Sound leaks like water. One unsealed gap around an outlet or a seam can undo an otherwise strong wall, so acoustical caulk and putty pads are not optional extras. They protect the rating you paid for.

These levers stack rather than add cleanly, and the right mix depends on your wall, your budget, and the noise you are fighting. The assembly described next combines mass, decoupling, damping, and sealing in a single build.

As we consider soundproofing a wall, it’s important to understand what is meant by a wall assembly. Thankfully, it’s straightforward: an assembly is a collection of components that make up a wall. Standard wall assemblies are typically either wood or metal studs with insulation between and drywall attached. This assembly isn’t great at soundproofing, as sound easily transmits through insulation and drywall. The answer then is to add additional components to the assembly so that the energy of sound waves are absorbed before it can make it through to the other side of the wall.

My go-to wall soundproofing assembly is to add AudioSeal® Mass Loaded Vinyl (MLV) Soundproofing Barrier, Green Glue Noiseproofing Compound, and RSIC Clips to standard studs and drywall. Let’s take a look at each component and see how they work.

While mass is an important aspect of soundproofing, so is the concept of decoupling. Decoupling materials in an assembly helps limit the transmission of sound vibrations. In combination with AudioSeal® Mass Loaded Vinyl Sound Barrier, adding resilient isolation clips will decouple walls to break the physical transmission of sound between structural components. The RSIC-1 stops the noise and vibrations that typically transfer through the structure. This will “float” your walls or ceilings, creating an air gap. These are used in conjunction with a double-leg hat track (resilient channel) that can be purchased via a local contractor supply. Once complete, drywall can be attached to the channel.

The third component of a powerful soundproof wall assembly is Green Glue applied between any subsequent layer of drywall. Green Glue provides a viscoelastic sound-damping layer that works like a resilient channel as part of the assembly. When installing the multiple layers of drywall, vary drywall substrate thickness and alternate your seams. This helps create a ‘tortured path’ for the sound. Allow Green Glue 30 days of drying time for optimal sound isolation performance with a minimum of 7 to 10 days of drying time before sound isolation will start to improve.

Blocking sound in a ceiling assembly follows the same principles as wall construction. Below is an example of a ceiling assembly using insulation, AudioSeal® Mass Loaded Vinyl Soundproofing Barrier, Resilient Isolation Clips, Green Glue, and multiple layers of sheetrock or drywall.

Although the concept of soundproofing flooring is very similar to walls and ceilings, different materials are used to impacts the main source of obtrusive noise that we want to block. Using Iso-step® Soundproofing Underlayment on the floor above provides an impact-resistant layer underneath the flooring. This will help prevent footfall noise and airborne sound from transmitting through the structure. To read more about using Iso-Step® Soundproofing Underlayment, read this post on using Iso-step® Soundproofing Underlayment to reduce Impact Noise.

If you want more information on how to soundproof and block sound, you may want to read these articles on Soundproofing a Garage, a Floor, a Window, a Door, Industrial Noise, and Soundproofing for Speech Privacy.

At Acoustical Solutions, our business is to find the best acoustic products and techniques to help our customers achieve the best results possible for their project. To learn more about soundproofing walls, the best modern materials to craft an assembly with, and specific ways to apply them to your unique situation, contact me today!