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A Complete Guide to Soundproofing and How to Soundproof a Room

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Table of Contents

How sound works in a room

Types of Noise: Airborne vs Impact

The difference between soundproofing and acoustics

Soundproofing vs Acoustic Treatments

The Basics of Soundproofing & Acoustics

What is an STC Rating?
How Sound Moves
What is NRC?

How to Soundproof a Room

3-Step Process
Soundproofing a Door
Soundproofing a Window
Soundproofing a Wall
Soundproofing a Ceiling
Soundproofing a Floor

There's a misconception that everyone at Second Skin loves quiet, that we're all hermits that sit in a padded room reading Charles Dickens novels with earplugs in because we hate sound.

Frankly, that couldn't be further from the truth, we love hosting friends and family, or watching the game too loud, or blasting AC/DC on our new stereo system. And sure, occasionally after a long day, flopping down on the couch and basking in silence can be pretty relaxing. But the point is we don't hate sound, in fact we love sound. What we do hate...is noise. And if you think about the process of soundproofing, that's all it really is, finding ways to target and keep out unwanted noise (actually, why isn't it called noiseproofing? We'll look into it).

We've worked with a lot of people over the years and have seen many reasons to soundproof your space, whether it's work or home. You may live in a noisy area near construction or loud bars, or have less-than-considerate neighbors that play their TV too loudly. Or maybe you're the noisy one and you are trying to keep sound in. Many of our clients are musicians or creators who work with power tools. Or maybe, like us, you just like to entertain and don't want to be a less-than-considerate neighbor. When people look to us for soundproofing solutions, it's not just about stopping noise, but to get the benefits that less noise can bring - helping reduce their stress, get better sleep, feel more comfortable, or be more productive.

Soundproofing is a simple concept but can feel really complicated and overwhelming once you start diving into it. We're going to try and share as much as we can about what we've learned over the years, from the basics of sound, to defining technical industry terms. If you read though this and feel like you still have questions, or if you just don't feel like reading, reach out to us directly and we'll help you with your soundproofing solutions.

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How Sound Works

Sound at its simplest form is just energy - technically a wave of energy traveling through molecules. That energy is created due to an object vibrating and transmitting that energy into the air or objects around it. A yell is the result of your focal cords vibrating. A loud bang is the vibration caused by two objects colliding. Sound energy can travel through all types of matter, but we like to categorize it as structural (traveling through something solid like metal or wood) and airborne (traveling through the air). Eventually, those vibrations reach the air inside our ears where we perceive the vibrations as sound. That's why we sell so much car sound deadening material. The vibrating metal of the car creates a lot of noise. The concepts start simple enough, but they can get tricky. Imagine a metal door. While the door may do a good job of preventing airborne sound waves from traveling through it, if someone were to bang on the door the sound on the other side could be quite loud. To effectively stop unwanted sound, you need to understand the different types of noises and the different types of sound treatments.


Types of Noise: Airborne vs Impact

Airborne

Airborne Noise

Airborne noise is sound that travels through the air, for example; loud talking, music or TV, a dog barking - these are all sound waves traveling through the air and then heard when they reach your ear. A metaphor we like to is how sound waves move like water; they flow towards the weakest point. Which means an effective, airtight barrier is key. Airborne sound waves find the path of least resistance to travel from space to space, once they collide with your barrier, they will try to find a gap. If they can't, they'll be forced to travel through the barrier.

Impact

Impact Noise

Unlike airborne noise which is defined by sound waves traveling through the air, impact noise (also called structure-borne noise) is sound that occurs as a result of one object "impacting" another and the vibrations being radiated through the object or to adjacent objects. Basically the difference between a bang in the other room, and a bang directly on the floor above you. Impact noise includes things like people walking or footfall, a ball bouncing, a chair rolling, or things being dropped on the floor. These noises are often so annoying because they are distinct and jarring - making them very noticeable. The key to reducing impact noise is to prevent the energy from ever entering the building's structure by dampening the vibrations.

The Difference Between
Soundproofing and Acoustics

When researching soundproofing solutions you'll often run into information about improving acoustics, it's important to understand that these are two distinct solutions to different problems.

Soundproofing (Blocking sound)

Noise is being created in the space I'm in or in an adjacent space, and I want to keep the sound from traveling from one space to the other.

Soundproofing

Acoustic Treatments (Absorbing Sound)

Noise is being created in the space I'm in, and I want to reduce the amount of time it's audible in that space.

Acoustic Treatments
Soundproofing
Acoustic Treatments

However improving acoustics involves using sound absorbing materials, like acoustic panels, which will absorb sound and prevent it from being reflected back into the room. Sound absorbing materials, while helpful in soundproofing projects, do not block sound. For instance, a popular acoustical material is acoustic foam. Open cell foam a very porous material and if you were to hold in front of your face while you speak, you'd still be able to hear your voice quite clearly. Foam is used over microphones, on top of speakers, and even over earphones, all proving it's not an effective sound blocking material.

Acoustic foam (or as those uninitiated on the Second Skin website may affectionately call "soundproofing foam") is not an acoustics option we recommend very often (although hydrophobic melamine foam is great for some applications like vehicles). People use foam often because it's the only kind of acoustic they know about. It's super cheap, easy to install, and it'll improve sound quality and reduce echo in a space. The problems are that it's not very durable and the cheap polyurethan foam is not Class A fire rated, so you can't legally install it in a commercial building. That's why we offer a huge variety of other acoustic material across a wide variety of spaces like a recording studio, gun range, or a space with loud machinery. Some options are very economical and then others are designed for a more professional setting like an office. That's where we may steer you towards sound dampening panels due to better aesthetics, durability, and requiring less space to be effective.

The fact is that each of these strategies are helpful in different ways. To help you understand how, let's break down soundproofing and acoustics further to illustrate how the two methods can work separately and together.

The Basics of Soundproofing

There are 3 main elements to consider when evaluating soundproofing products.

Mass

Sound is really nothing more than vibrations. Sound travels from room to room by sending vibrations through the wall. The more mass something has, the more difficult it is to vibrate, therefore, by adding mass to a given material, you can increase its ability to block sound.

Limpness

Now this may seem counter-intuitive. But the less stiff a material is, the better it will be at blocking sound. This is because a limper material is harder to vibrate. Think about the difference between throwing a ball at a bedsheet versus at a piece of metal. The bedsheet's limpness allows it to absorb the ball's energy without the impact noise.

Airtight

This one is pretty straight forward. Like water, sound will find gaps and go straight through them. We call these openings sound leaks or flanking paths. Creating an airtight barrier and sealing up gaps will keep sound waves from finding their way to you.

It's important to understand that these three tenants of soundproofing need to ALL be in place to be effective. A material that's heavy but has gaps, or a material that's limp but not heavy, won't cut it.

What is an STC Rating?

When researching common materials for soundproofing, you may see products or combinations of products that talk about their STC rating. STC, or Sound Transmission Class is an agreed upon system used in the US to measure how well (or how poorly) sound waves get through ceilings and walls. As STC is used primarily on home and commercial construction, it bases it's measurements on sound that it's in the range of 125 - 4000Hz, which includes the range of normal human voices and other frequencies you'd most likely run into in a residential or office building. A poorly built wall that doesn't block much sound would score an STC rating of about 20 - 25, while a VIP suite built to keep out all sound would rate at least 60. The wall of your average suburban home rates between 30 and 45.

Mass Law Curve

STC does not measure how many decibels a material can block, so if you have a soundproof wall that has an STC rating of 40, that *does not* mean it can block 40 dB of sound. STC ratings also cannot be added together. If you have a material with an STC rating of 30, and another material with a rating of 20, adding them together does not give you a rating of 50. In fact, the STC rating would probably be closer to 35.

An illustration of this is the "Mass Law Curve". We've mentioned that weight is a key tenant of soundproofing. When you double the weight (measured in pounds per square foot) of a material, you can expect to increase the STC rating by 5.

However eventually the 'curve' part of the Mass Law Curve kicks in as you do run into the law of diminishing returns. Eventually, it becomes impractical to double the weight to continue increasing STC.

The Basics of Acoustics

So now that we've run through the basics of soundproofing, let's talk about acoustics. When people talk about improving acoustics, they are trying to increase the sound quality in a space by reducing the amount of noise. This is usually done through implementing acoustic panels or other sound absorbing materials for reverberation and echo control and for noise reduction.

As we mentioned before soundproofing is all about blocking sound, and acoustics is about absorbing sound. While both of these things aim to reduce noise, improving acoustics has a specific goal of increasing sound quality in a space. To understand when and why you should focus on acoustics, you need to understand how sound moves.

How Sound Moves

The world of acoustics is made up of two types of environments, free fields and reverberant fields. A free field is a space where sound waves are unobstructed by any reflective surfaces, think of a literal giant open field. In this type of environment sound travels outward in every direction from the source spherically. In a free field you can expect sound to decrease by 6 dB every time you double the distance from the source.

How Sound Moves

However indoors, you don't have the luxury of distance to dissipate sound. Noise will build as the sound waves run into hard surfaces and bounce back, over time the sound dissipates but only after it's reverberated throughout the room. You've probably experienced this if you've ever been in an empty house before it's been furnished or decorated. In an environment like this, even speaking in a quiet voice seems amplified.

If these are the types of problems you're trying to solve you should pursue acoustic treatments and sound absorption materials. See! We got there eventually. Note that sound absorption, like the mass law, also falls victim to diminishing returns. Each doubling of sound absorption material will reduce noise about 3 dB, up to a practical maximum of about 10 decibels (if the room started with no sound absorption). Each doubling will also cut the reverberation time in half, which means it takes half the time for sound to reduce to near-nothing once the source stops.

What is NRC?

What is NRC?

Earlier we talked about the STC, which is a rating to help measure the effectiveness of sound blocking materials. Similarly there is a measure for the effectiveness of sound absorbing materials. The Noise Reduction Coefficient, or NRC rating, measures how well materials can absorb sound. The rating uses a 0 to 1.0 scale based on an average of the sound absorption coefficients at 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz rounded to the nearest 0.05. The resulting number can be used as a rough approximation of how much sound a material absorbs. So open air has an NRC of 1.0 absorbing 100% of the sound and reflecting none of it, but a brick wall has an NRC of .05 only absorbing 5% of the sound and reflecting back 95% of it.

How to Soundproof a Room

Ok, so now that you're practically a sound engineer, let's get started with your actual soundproofing project.
Before you go off and start buying up material, you should plan your strategy.

Step 1 Consider the Noise Source

Firstly, identify the noise issues. I know this sounds obvious, but people often jump into complex soundproofing projects when they could just treat the source. Are you trying to block out your kid's band practice in the garage? See if you can find another location for them to play. Trying to drown out that outdoor noise coming from your HVAC unit? Don't soundproof your room. Build a soundproof enclosure or soundproof fence with the Quiet Quilt sound blanket for your unit instead.

Step 2 Decide Where to Soundproof

Understanding where to add soundproofing is absolutely key. Sound is best reduced by blocking sound at the source, blocking sound at the receiver, or increasing the distance between the sound and the receiver. For example if you were sitting 20 feet from a loud stereo, adding a barrier right in the middle at 10 feet would be the least effective strategy. Instead you could; (1) put the stereo even further away, (2) create a box around the stereo (blocking the source), or (3) put in earplugs (blocking the receiver).

Step 3 Determine How Sound is Getting In

Once you've identified the sources of noise, determine the path it's taking. Is there anything between you and the noise? Is it coming from inside the building? Is it above or below you? Any soundproofing barrier you create is only as good as its weakest point. Sound behaves a lot like water, and it'll find its way through even the smallest gaps. If you have big gaps, priority #1 is to plug them up so that your room is like a swimming pool with no leaks. In most rooms, the biggest sound leaks are around the windows and doors, but we're going to walk you through how to soundproof each part of a room.

Soundproofing a Door

Doors are a weak point for sound because they're also a weak point for air. Air carries sound, ergo, sound gets through your door. As the weakest link for letting sound in, there are two major things to consider to effectively soundproof a door: the mass of the door and whether there are any gaps between the door panel and frame. That's it. That's all you need to solve.

The average STC of a typical wall in your house is 32, while many types of doors are much lower than that. Because doors are a weak point for sound, this lowers the overall effectiveness of sound blocking for your entire wall if there's a door in it - even if it's closed.

Type of Door STC Rating

Louvered Door

Your typical louvered door is about 25% open. You're done before you even start. Might as well leave the door open… Come on in!

12

Hollow Core Door

Typically used as bedroom doors or any other in-home entryways, these are made of fiberboard or laminated wood and (true to their name) are mostly empty inside. These doors are lightweight, easy to install, and aren't super expensive. On the downside, hollow core doors are fragile and do little to stop sound from passing through.

17 - 20

Solid Core Door

These doors are significantly heavier, made up of a combination of wood and wood byproducts, and are usually used to partition your home or apartment from the outdoors. They're more expensive but thanks to their density, solid core doors are able to do a better job of blocking out noise.

30 - 35

Once you determine the types of doors in your space, the other key to remember is the gaps around the door. Your typical door can easily have 1 sq ft of airspace around it. Not good. Fortunately, there are a few things you can do to improve the soundproofing.

Solid Core Doors

If you have hollow core or louvered doors, replace them with solid doors, or add mass with soundproof blankets or mass loaded vinyl. Note that adding material to a door may not be the most aesthetically pleasing solution.

Sound Lock Door Seal Kit

It may not look like much, but like we just said… the gaps around your door can often add up to nearly 1 square foot of space. Imagine a foot-wide hole in the middle of your wall! Seal up these gaps with a door seal kit. These kits are fairly easy to install and cost-effective. Be sure to measure your door and frame thoroughly before-hand.

Soundproof Door

If significant sound blocking is key in your space, To really keep things quiet you can install an acoustic door. Often used in recording studios, offices, conference rooms, hotels, and dorms, acoustic doors have an STC rating up to 56.

Soundproofing a Window

Windows have a similar problem to doors in that they're also a weak point in your wall. Again, the key components here are sealing up gaps, and adding mass. Like doors, not all windows are made the same and some are better at sound blocking than others.

Type of Window STC Rating

Monolithic Float Glass: 1/8" or 1/4"

This is standard glass produced using the tempered glass float process. Thicker glass has more density, so it blocks more sound.

26 or 31

Double Paned Glass: ¼" and ⅛" with a 2" air gap

By adding an air gap between two panes of glass of different thicknesses, STC rating is substantially improved. Any air gap should be at least ½", and a bigger gap improves soundproofing.

39

Double Paned Glass: ¼" laminated and 3/16" monolithic
with a 2" air gap

Laminated glass features a PVB sandwiched between two layers of glass to better block sound. The laminated glass should always be on the warm side of the window.

45

Of course replacing your windows is always an option, but that cost can start to add up. And if not installed properly, you may even be worse off than when you started. If you don't feel like replacing windows is the right option for you, or you want additional sound blocking, here are a few options.

Soundproof Curtains

Adding soundproof blankets or curtains are an effective, albeit not always practical solution. To get the most out of soundproof blankets or curtains, you'll need to seal the edges and essentially block out the window.

Fantastic Frame Window Inserts

A more practical and visually appealing solution is installing a climate seal insert. In addition to helping with sound, it can actually help with temperature control to reduce your heating and cooling costs. They can also be removed as needed so you don't lose access to your windows.

Soundproof Windows

Similar to our suggestion for doors, the ultimate soundproofing solution for windows, is to install a soundproof window. As the name implies, this product is designed specifically for blocking sound with STC ratings over 45.

Soundproofing a Wall

Sometimes sealing up doors and windows isn't enough. Or maybe you're just dealing with a wall that just isn't cutting it. As with any soundproofing project, start by finding any weak points. Along with treating any doors or windows, use caulking or acoustic sealant around outlets, switches, vents and any other potential gaps. Identifying and treating gaps may be enough to find the volume you're comfortable with, if not you can take things a bit further.

soundproof_a_wall Created with Sketch.

MLV or Green Glue

As always adding mass is a key component in helping to block sound. You can do this in several ways, but we always recommend ⅝" drywall for any project where soundproofing mattters. For good soundproofing, you should apply mass loaded vinyl to the studs before the drywall or add a second layer of drywall with Green Glue as a decoupling layer between the two sheets of sheetrock. For either method, you'll need acooustical caulk to seal up around the perimeter and around any penetrations in the wall.

RSIC Clips

This solution is a bit more complex and involves a process called decoupling. Sound moves as vibrations through a structure, if you can separate - or decouple - the structure some way, it creates a gap that makes it more difficult for vibrations to cross. Use resilient sound isolation clips (or RSIC) and 25 gauge aluminum hat channel to attach ⅝" drywall, which allows you to "float" the drywall, making it more difficult for impact sound to travel through your structure.

RSIC Clips + Green Glue

You can take our previous suggestion to the next level by adding a 2nd layer of 5/8" drywall with Green Glue between the two layers. This will substantially increase the density of your wall and if done right, adds 5+ STC point. That extra density is key if you want to continue blocking more sound.

Soundproofing a Ceiling

Noise you are hearing through your ceiling may not necessarily be coming above you. It's possible that airborne noise is travelling up and over your wall through gaps like air vents. You can use the same strategies for soundproofing walls on your ceiling. But since most of what you hear from your ceiling is impact noise, ideally you treat your ceiling and floor assemblies together.

Green Glue

Add mass with an additional layer of ⅝" drywall on your existing ceiling. We recommend you apply the drywall with a common noiseproofing product called Green Glue which is excellent in stopping sound from transferring through materials.

RSIC Clips

Decouple your ceiling by adding the ⅝" drywall with resilient sound isolation clips, or RSIC, which will "float" the drywall and make it more difficult for sound to vibrate through your structure. If you're going this route, make sure to add insulation in the gap above the ceiling if there isn't some already there to increase the effectiveness of the ceiling assembly.

RSIC Clips + Green Glue

Take our previous suggestion to the next level by replacing the standard drywall with SoundBreak Wall Board. SoundBreak is a high STC rated gypsum board that will give you maximum sound blocking.

Soundproofing a Floor

You may be trying to block sound coming from beneath you, but usually treating the floor is to protect the room below. Either way soundproofing your floor will help with the transfer of noise in either direction.

Thick Carpets

Add mass with an additional layer of ⅝" drywall to create a better sound barrier on your existing ceiling. We recommend you apply the drywall with a common noiseproofing product called Green Glue which is excellent in stopping sound from transferring through materials.

Rubber Floor Underlayment

Decouple your ceiling by adding the ⅝" drywall with resilient sound isolation clips, or RSIC, which will "float" the drywall and make it more difficult for sound to vibrate through your structure. If you're going this route, make sure to add insulation in the gap above the ceiling if there isn't some already there to increase the effectiveness of the ceiling assembly.

You Did It!

Congratulations, you now have your soundproofing phD. We'll be sending your copy in the mail for you to frame and hang on your newly soundproof wall.

Ok, so not quite - but you certainly know enough to school your friends and family. Soundproofing is complex, but we hope that now you have the knowledge to identify your specific soundproofing problem and start to make a plan. We've been doing this for a long time, and helped a lot of people with a variety of different issues and circumstances. We know that some of this is easier said than done.

Before you tackle your soundproofing project, reach out. We're here to help you figure out the right materials, and the right strategy.