Soundproofing vs. Sound Absorption

I have been getting a lot of calls lately where people are looking to soundproof a room. They explain to me that they want sound that is being made within the room to STAY in the room or they want to keep sound out of their space. We commonly begin talking about the room and the type of noise that we are dealing with in each particular situation.

A LOT of people ask for pricing on sound absorbing foam, or sound proofing panels. They are sure that foam is the ticket because people have seen “egg crate” foam or other similar products as finish wall treatments in recording studios, on TV shows and in movies. This misconception is INCREDIBLY common – so if you are reading this thinking to yourself, “Well, self, doesn’t foam stop sound? Isn’t foam used for soundproofing a room? Everyone knows that, right?” Unfortunately I have to tell you that you are wrong. Foam does not stop sound, foam absorbs echo. Don’t feel bad. There are lots and lots of people out there that share this idea.

There are two sides of the acoustical coin, if you will. There are products that absorb echo within a room and there are products that will block or stop a sound. (There are some panels that will do both. These are generally called composites, but if I get into that now, things will be confusing so I am going to keep it simple.) Products that are designed and intended to ABSORB ECHO within a room are soft, light, fluffy products. They will generally feel soft to the touch. They are designed to soften up the surfaces that are in the room and reduce the echo within that space.

Products that are designed to BLOCK SOUND from entering or leaving a space are almost always found INSIDE the wall construction. These products are heavy, dense, cumbersome, or designed to decouple the wall so that one side of the wall doesn’t have hard surface contact with the either.

I’m going to throw a couple ‘for instances’ at you here to hopefully help further my point. Imagine you are finishing a room in your basement. You have installed the studs that will frame the wall and you are to the point where you are ready for sheet rock. Rather than sheet rock, you decide that you are going to put some 2″ Thick, white “egg crate” foam on the studs. This foam has almost no mass and no density. It is mostly air. After you’ve installed the foam, you tell someone to go stand on the opposite side of the wall and you begin talking. You will be able to hear each other as if there were no wall in front of you.

New scenario. Same basement – same stud wall. Rather than foam, this time, you decide that you are going to put twelve layers of 5/8″ sheet rock on either side of the wall. Twelve layers on the inside, and twelve layers on the outside. You tell your friend to go to the other side of the wall and you start talking. I would be willing to bet that your friend would not be able to hear much of what you were saying due to the massive amount of mass that is making the wall.

Ok, new room. This room is made out of concrete and is the exact same size as a racquetball ball court (20′ wide by 40′ long x 20′ tall) and is made out of solid concrete. The walls of this room are two-feet thick. You clap your hands in the room and the echo seems to go on forever. You have, in your hands 100 new super-balls of varying colors. You throw them in every direction and they keep bouncing and bouncing everywhere through the room, and eventually they stop but it takes a few minutes. NOW imagine that you line that same room with 2″ thick foam. You line the walls, ceiling and floor. You throw the same 100 super-balls and they hit the wall/ceiling/floor and don’t bounce. The energy from the ball was absorbed into the room. A sound wave inside this room is just like that super-ball. It is reflected off of a hard surface and absorbed by a soft one.

I know that these examples are fairly crude, but hopefully I have painted a picture that helps you understand a little more about sound proofing and sound absorbing. I’m sure there are lots and lots of people out there that are excessively smarter than I am who are shaking their heads because I did not touch on the technical side of things explaining wavelength and frequency, but oh well. I am trying to lay down a very simple framework that will help the average Joe’s and Mary’s of the world understand the difference between these two principles of acoustics

Generally speaking, absorbing echo within a room is pretty easy. Based on the surfaces that make up the room and the size or volume of that room, it is fairly easy to suggest to potential customers a few different products and a pretty safe quantity of each product that will take care of their problem. Blocking sound, or decreasing sound transmission, however, is usually a much more difficult feat to accomplish. There are a LOT more things that come into play and blocking sound or soundproofing a room usually is going to require some kind of construction because the stuff that is doing the work is inside of the wall assembly, not on the surface of the sheet rock. Of course there are some products that can block sound that are finish wall surfaces, I am making a generalization.

If you have an acoustical problem or situation that you are looking to fix, the understanding of these two ideas is going to greatly help you choose a product or products that will help reduce or eliminate the problem. I do not want to get into product suggestions in this little write-up, I wanted to put something together that was more informational than anything else. If you would like to talk to someone about your particular problem, here are some things to put together that will help both you, and the sales person that you talk to.

  1. Are you looking to block sound or absorb echo?
  2. What are the dimensions of and surfaces in your room?
  3. What is the room used for? What types of sound(s) are you looking to block/absorb? (high pitch-squeaky sound, voices, low frequency-bass type sound, all of the above)
  4. What are your ideas as to the best way to treat the room, where to put product, or how to approach the situation?

6 Comments

  1. Ankit

    Hi Ted. Great article you published. I am actually looking for some advice.

    I built a small room which is almost perfect for the purpose of soundproofing with just one thing – the door. the walls are 4.5 + 4.5 inches, with glass wool filling in between.

    The advice I am looking for is what material is Ideal for the door to block sound (and yes, I am not looking for absorbing the sound completely if possible). The purpose of the room is that sound should somewhat echo !!! 🙂

  2. Ted W

    Ankit,

    Thanks for the compliment on the article, I’m glad it helped!!! It is my assumption that you are trying to BLOCK sound from coming into our out of this room – is that correct? If so, there are a few things to look for and to keep in mind.

    Imagine if this room were filled from floor to ceiling with water. Where is the first place that water would use to get out? You can likely picture the water leaking under and out from around the door. The physics of water pressure and sound pressure are similar – they both use the path of least resistance first. Even a pin-hole can drain a fish tank. If you have ANY air gaps around or under the door, these areas need to be sealed before anything else. You could put 3′ of lead on the door and you would have the same problem. And, to further this point, if you have a 1% air gap in a wall (1/8″ between the door and the floor) and 30% of the sound in that room will leak out of that air space. Further, if the air gap is 5% of the wall area, 90% leaks out of the room.

    So, I generally tell people to use light as a test. Turn the lights off in the space and close the door (assuming the lights are on outside of the room) if you can see ANY light, start there. I have had people use common weather stripping to seal the door but we also have a few different door seal kits. These kits include door bottoms that lower a neoprene rubber gasket to the ground as the door is closed.

    So, let me know about the seal under and around the door. If you already have something like this in place, we will take it to the next step.

    Thank you!

    Ted

  3. Ana

    hi!
    1st, i need to express how happy i am w/ your blog & vast knowledge & desire to help & explain it in very human terms! thank you very much for detailing every issue so well.

    i make / perform electronic music & live in a duplex on the bottom floor. my studio is in our basement in a room that is maybe 200sq ft, directly under our living room, so there is 1 entire floor separating me from my upstairs neighbors. but.. it’s not the volume so much that bothers them, it’s really the bass, however i do want to tackle both variables. i rent this home/studio so i cannot do anything structural to the space but i’m convinced that affordable ornaments/wall or ceiling surfaces that can greatly help from the sound from traveling up into my neighbors bedrooms. there’s just so much product out there in the world & i don’t know what will best suit my needs. the room does have 3 very small windows, mostly wall that’s about 9′ high w/ the lower 1/3 being brick.

    i know that soundproofing will be impossible, but confident that anything better than nothing (which i currently have) will help a lot!

    thanks for your time & smarts!

  4. Jennifer

    Hi Ankit

    Thanks for the info – a simple Jane like me now understands clearly the difference between blocking and absorbing sound. Wish more professional people could learn to speak our language it makes what we need to ask simpler.

    We live in Florida South Africa – a building with 148 units built square with a large court yard in the middle. We are on the 1st floor directly looking into the courtyard and overlooking a garden on the other side of our flat. Our problem is two fold – we need a sound blocking front door to block out rowdy children and inconsiderate adults who speak to each other over each other in the passageway as we are also located two metres away from the stairwell and elevator and the courtyard play area.

    On the other side we have full 3m high x 11m wide standard residential glass windows on the side of our patio/study and main bedroom. They have now installed 3 massive heating pumps 4oom from these windows and the noise is driving us to pills…. I need to know what type of glass we can source that is firstly blocks the sound and is non reflective. The windows face a main street entrance and is north facing so we are trying for a solution to best assist on all levels but mostly block out as much noise as possible.

    I will truly appreciate your advice in trying to resolve this problems.

    Kind Regards

    Jennifer

  5. hans charles

    i have a one car garage that is situated under my tenant’s apartmentand also it is sharing my ground level studio apt.I want tochange this garage into a theater room ,where i don’t want to bothere my tenants with the noise .What advise can you please give me in order for the sound not to travel tru.
    thanks

    • Ted W

      The question you ask is relatively simple, but the answer however, can be extremely complicated. Like building a race car or a computer, there is not a right and/or wrong way to proceed — it is ALWAYS very situation-specific. I would suggest not using any kind of subwoofer/low-frequency and building a room within a room. Exactly what building components to use is far too site-specific for me to try to approach without more information.

      Thanks,
      Ted

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