Soundproofing 101

Soundproofing 101

Author: Eric Dellolio

Last Updated: Feb. 9, 2024

Read Time: 12 Minutes

Soundproofing 101


Eric Dellolio

Last Updated:

February 9, 2024

Read Time:

12 Minutes

Author: Eric Dellolio

Updated: Feb. 9, 2024

Read Time: 12 Minutes

Soundproofing may seem like a daunting DIY task, but with the right advice and proper knowledge, you can go on your way to completing your first soundproofing project in the right way. Before you begin soundproofing anything, it is important to understand the basics of the subject so that you know what you are doing and why.

In this article, we will break down this complex topic into digestible sizes. Most people won’t have studied this topic since middle school (or ever), and even then didn’t go into the depths we will go here. So are you ready for a soundproofing primer?

Soundproofing may seem like a daunting DIY task, but with the right advice and proper knowledge, you can go on your way to completing your first soundproofing project in the right way. Before you begin soundproofing anything, it is important to understand the basics of the subject so that you know what you are doing and why.

In this article, we will break down this complex topic into digestible sizes. Most people won’t have studied this topic since middle school (or ever), and even then didn’t go into the depths we will go here. So are you ready for a soundproofing primer?

Soundproofing Materials

(Sound Blocking)

Acoustics Materials

(Sound Absorbing)

Soundproofing Techniques: Understanding Sound

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 vocal 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 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 simile we like to use 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.


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.


(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.


(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.

However improving acoustics involves using sound absorbing materials, 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 acoustical material 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 materials.


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. A great product for this is mass loaded vinyl, or often times extra layers of drywall


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.


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.

  What is an STC Rating?

What's an STC Rating?

When researching building 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.

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.

What Does Acoustics Mean?

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 sound absorbing materials for reverberation and echo control and for noise reduction. Learn more about the difference between echo and reverb.

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.

However indoors, you don't have the luxury of distance to dissipate sound. In reverberant fields, 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?

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.

FAQs on Soundproofing Basics

How to Block Sound

A cheaply made door or wall isn’t going to efficiently reduce noise. There are two essential factors that go into blocking sound:

  • Density - In order for a barrier to be soundproof, it needs to be dense enough to stop sound waves from passing through. This is why we generally only recommend solid core doors, and walls that have ⅝” thick drywall on each side with insulation in between.
  • Airtight seal - Even an incredibly dense barrier will be useless if there are air gaps around it. Any penetrations and gaps around your door, wall, window, or ceiling allow sound to travel through. Although these small gaps may not seem like much, if you do not seal up the perimeter of your barrier with acoustical sealant, you will seriously impair the performance of your barrier. Even a 1% air gap in a wall is a serious issue. Imagine how much sound would come through if you had a baseball-sized hole in your window!

Do Acoustic Panels Work for Soundproofing?

It is a common misconception that acoustical materials can be used for soundproofing projects. Acoustic panels are not effective for soundproofing applications. This is because they are generally lightweight and lack density (which is a must for sound blocking). Acoustic panels are sound absorbent, meaning that they reduce the reflectiveness of a surface and minimize the echo and reverb in a room. Acoustical materials are great for improving the sound quality of a room, but shouldn’t be used for soundproofing.

How Do You Soundproof a Room?

In order to soundproof a room, you’ll need to focus on addressing the entry points for noise. This would be any weak points and gaps in the room that may allow airborne noise to travel through. The most common weak points to address are the entryways, such as the doors and windows. Using a product like our Fantastic Frame Soundproof Window Inserts or our Door Seal Kit can help to improve the STC rating of your doors and windows.

Once you have properly soundproofed your entryways, if additional sound reduction is needed you will also need to soundproof your walls, ceilings, and floor. Any barrier that is poorly constructed or built with too many gaps will allow sound to travel through. So, to soundproof your room, here are a few of our top tips:

• Use Acoustical Sealant to go over every crack and gap in your walls, ceiling, and floor.
• Add density to your walls and ceiling by adding another layer of ⅝” drywall in conjunction with our Green Glue between the two layers.
• Use our UnderBlock Rubber Floor Underlayment to prevent airborne and impact noise from traveling through the floor.
• Make sure you have a solid core door and invest in our Sound Lock Door Seal to seal the gaps around it.
• Fit any existing windows with a Fantastic Frame Window Insert.

It’s always easier to plan for soundproofing from the beginning, but the above strategy would work incredible for any room you need to retrofit. For more information on how to soundproof your room, check out our full guide here!

How To Get Rid of Echo in a Room

Reverb occurs in a room when sound vibrations reflect off the walls, ceiling, or floor. Use sound absorption to reduce the reflectiveness of the surfaces in a room and absorb that reverberating sound. You can use high-quality, aesthetically pleasing acoustic panels such as our Acoustics Pro panels and PolyZorbe, or a more budget-friendly option like CelluZorbe or EcoVerb. Any amount of absorption you add to the room will improve the sound quality, but if you want to get the sound “just right” then you should reach out to one of our acoustics professionals for a recommendation and acoustical analysis.

Have questions about your project?

Call us at 1.800.679.8511