# Build a Soundproof Wall

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Up until recently, the only thing between my room and the one adjoining was a set of double doors. I like living with people and do so by choice, but being able to hear someone's entire phone conversation word for word seemed a little much. So I set out to build a more proper wall between us, and in the process learned quite a bit about soundproofing. It worked out great, as now we can barely hear each other when talking at a normal volume. Success!

## Step 1: Principles of Soundproofing

In planning what I was going to build, I needed to first understand more about soundproofing. I am by no means an expert, but just learning the basics went a long way. There are 5 basic principles of soundproofing: mass, absorption, conduction, mechanical decoupling and resonance. Read on for a brief overview of each principle and how I addressed it.

Mass: This one is pretty straightforward. More density = more sound absorption. Thing is, you need it to be REALLY dense to make a big difference, so simply adding a layer of drywall to an existing wall will only give you a slight decrease in sound transmission. To address this principle I used two layers of the thickest drywall readily available (5/8") vs the more common 1/2" thickness.

Absorption: Any kind of insulation within a wall's cavity will help absorb some sound, although it will not trap any low frequencies. This is most effective when the walls are decoupled, as if there are studs connecting the two walls the effect of the insulation will be minimal. Still, putting something in the wall is better than nothing, so I insulated my wall with standard R-13 fiberglass insulation.

Conduction: This is the transmission of sound through vibration of solid objects connected to each other. Conduction is a very efficient way to transmit sound, and as such any wall that has drywall directly connected to the studs on either side will never perform well. Sound will also travel through indirect routes largely via conduction, and this is called flanking noise. In my case I could do little to address this principle, as the nice solid doorway around my wall would always be a good conductor of sound and the weakest link between our two rooms.

Mechanical Decoupling/Isolation: This is one of the most effective ways to combat conduction, and is why the most effective soundproof walls are completely decoupled, so there is no direct path for the sound to travel. If not paired with other soundproofing principles, decoupling a wall will help with transmission of mid-high frequency sound but will increase resonance and sound transmission at lower frequencies (more on that below), so it must be done in combination with other principles to be truly effective. To address this I kept my wall detached from the double doors rather than attaching my framing directly to them, however I'm not sure if this made much of a difference considering the conduction of sound through the surrounding doorway would probably outweigh any effort made on this principle.

Resonance: Despite best efforts on all of the above principles, sound will still resonate a well insulated, decoupled wall if it hits the right frequency to vibrate the components of the wall. This isn't common in high frequencies, but is a challenge for low frequencies (imagine how strong bass rumbles certain objects at particular frequencies, therefore a decoupled wall will rumble x2 when the right frequency is hit for the mass of the wall). Not to fear, this is offset in two ways:

• Lowering the resonant frequency of the wall: one can lower the frequency at which the wall wants to resonate by making sure there is plenty of mass in each wall (tougher to vibrate), and by adding insulation / plenty of air in between (absorption). This can help push the resonance point low enough that only the deepest frequencies will vibrate through the wall. Sadly this is why your subwoofer will almost always annoy the neighbors, as these methods can only push the resonant frequency so low.

• Damping: this refers to any means of reducing resonance altogether by absorbing or redirecting sound, and can go a long way to combat resonance and conduction. By far the most effective damping agent out there is green glue, and from all the specs I've seen it's likely the single most effective soundproofing aspect of my wall. I used the compound to cover the area of my wall, and sealant to fill the seams.

Asleep yet? No? Great! If you're like me and found this all very interesting, here is some more reading on the principles, and how decoupling works. Moving along, let's build a wall!

## Step 2: What You Need

I was filling a 5x7 space, so roughly the same square footage as one sheet of material. Adjust what is listed below according to the area of your wall.

• Framing supplies - enough to frame the outside of your "wall" and 1" struts every 16" to hold the insulation in place
• R-13 insulation
• Two tubes of green glue noiseproofing compound per 4x8 area of coverage *
• One tube of green glue sealant *
• Full sized caulk gun for green glue
• Drywall - enough for two layers (you will be making a green glue sandwich)
• 3" Drywall screws
• Basic building supplies (drill, rock knife, masking tape, ruler)
• Safety equipment (face mask, gloves, glasses)

* Green glue products are specialty building supplies, and are not available at standard building stores like home depot. I googled for a green glue distributor in my area and found one, but there is also this list of distributors on the green glue website, and this one sells them online. You can also get green glue on amazon, but only by the case.

## Step 3: Frame the Wall

Build a frame for your wall, with studs 16" apart if you are using standard insulation. In order to add any potential decrease in sound transmission, I left a two inch gap between where my wall would be and the double doors as a means of decoupling (see step 1). One important thing I neglected when I framed it was that I could have used a stud along both seams of drywall to properly attach them down, which I figured I could get away without given the small size of the wall. It ended up looking OK, but the seams would have been much cleaner if I'd done this. Don't make the same mistake!

Once your frame is built, I put down a few layers of tape to protect the floor, and attached it to the doorway. Take care to keep the frame plumb as you go. This was achieved easily enough on the sides and top by wrangling it to a straight line as I screwed around the doorframe. However along the floor I had to get crafty and used some spacers to push out the warp in the wood to a straight line, as I didn't want to use any screws in the floor.

## Step 4: Insulate the Wall

Next I added the insulation. I ended up taking it out of the casing because it stuck to the frame better. Wear all your protective gear! Fiberglass is nasty stuff that you don't want in your eyes, lungs, or skin.

## Step 5: Cut Drywall to Size

As the main part of the wall is green glue sandwiched between two layers of drywall, I first cut two layers of drywall to size, being sure to stagger where the seam would be for more sound isolation and ease of construction.

To cut drywall, you can simply use a rock knife to score, then lay the board over a raised surface to break the seam. It can also be cut by any saw or power tool you have in your shop. I went for a tight fit, but you will be filling the seams with soundproof caulk, so anything up to a 1/4" gap is not a big deal.

This step was by far the most irritating for me as I live in an old house where none of the measurements are uniform. Measure your doorway thoroughly first, because it's much easier to make one cut in drywall than make small adjustments!

## Step 6: First Layer of Drywall

Attach the first layer of drywall to the frame with drywall screws every 16" or so. When finished fill all of the seams with green glue sealant (might not be necessary to caulk both layers of drywall, but I figured I might as well).

Let the sealant dry for 24 hours.

## Step 7: Green Glue!

Here's the fun part! Position your second layer of drywall for easy attachment to the wall, and squiggle two tubes of green glue onto them. Using a random pattern like this is the recommended method. Quickly lift and attach the drywall while the green glue is still wet, with screws around 16" apart.

## Step 8: Caulk the Seams, and Done!

Caulk the final set of seams, and your wall is complete!

Well, at least from a soundproofing perspective :) At this point I was sick of construction and called myself done. However to really finish the wall, you will want to tape and mud the seams, add texture, then paint it. Details, details...

Visual appearance aside, this wall has performed amazingly well, despite the obvious conduction that I'd never fix from the doorway and the old walls that I did nothing about. Whereas we used to hear each other's every word, now quiet talking is barely audible, and medium to loud talking is audible but muffled and significantly quieter than it used to be. All in all, a big improvement.

Happy soundproofing!

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## 216 Discussions

I have lived in apartments that had "Music lovers" as neighbors, and found that a floating wall of Paper egg cartons helped a lot. Combine that with the wall you built and use cork instead of drywall and you have almost the same as professional music studio walls.

14 replies

Egg cartons are used even when people are building low level recording studios. I've seen a lot of them. Egg carton "deflects" a lot of sound, thus cancels the echo/reverberation. From my expirience it was able to withstand quite successfully
(With some additional soundproofing) our band in a garage (drum set, 2 guitars, bass) :)

Do you know the makeup of professional studio walls? Id be interested to know what exactly is layered in there. I've heard egg cartons work well but never spoke to someone that tried it, thanks for sharing!

Professional studios are floated on all 6 sides, the most intense ones are built with shock absorption. There are often several layers of absorption underneath the flooring, and one of the most important things I was surprised not mentioned in this is that AIR is the best deadener of sound. All recording studios built modernly have an open air insulation corridor within the 6 surrounding barriers, and the room itself is floated from the 4 walls with at least 6" of air space.

Another issue not raised here are the following, which should be taken into account:

LFE (low frequency emission) is omnidirectional. The lower a sine wave, the longer the maturation of the wave. A sine wave of 30Hz matures fully (goes through an entire power cycle back to 0º) after like 400 feet. So if you have a sub, you are sending LFE out in every direction simultaneously in 360º 3 D space. You can't stop LFE with water, cement, steel (of course it will deaden), the best way to deter that low frequency from proliferation is to deaden it with air.

The Fletcher-Munsen Curve

Humans are most sensitive to specific frequencies. Human voice, the cry of a baby, sounds of prey moving at a distance, the sound of oncoming danger (lets just call that rumble). So, you are most sensitive to your neighbor's crying baby 3 doors down the hall than you are your neighbor next door playing Call of Duty with no sub. Your brain and ear WANT to hear 1,500 hz - 5,500 hz (relatively) over everything else. If you are trying to specifically cut back on transmission for neighbors in close quarters, kill the shit out of frequency under 60 hz (steep roll it off, bro, I'm not saying attenuate slowly to 30 hz, lol) and make sure and kill that high mid/mid highs.

Egg crates are used as "soundproofing" by deflecting frequencies in a varied pattern, cutting down heavily on return reflection, egg crates will only stop frequencies that would otherwise be harmonic resonance to a wall, they are used for batting purposes, they do not "sound proof."

Unless you are talking about "Egg Crate" shaped pads, either mattresses or acoustic baffling, made by Auralex and such, but it's the same principle. A towel or an egg crate isn't going to protect you from the Low Rider going down your street.

Hope all that helps everyone who reads it, lol.

Egg cartons, carpet on the ceiling, felt wallpaper etc is not an attempt to soundproof as such, but to improve the acoustics of the room, typically reducing echo.

Rather than using egg cartons, I recommend using high-density closed-cell foam. While I'm not endorsing Auralex brand, that's the brand I've used to great effect. 4-inch foam, while more expensive, is best, as it reduces low-frequency reverb as well as high-frequency.

It certainly makes sense that a thick layer of foam would be more effective than a single layer of cardboard. Auralex brand is useful for Googling to see what you mean, and in doing so I see it's rather expensive and strongly resembles foam pipe insulation, which is more reasonably priced. Do you think pipe insulation, arranged in "panels" would work just as well?

Sad to say, I haven't done a qualitative study to know for sure. It certainly seems that if so, it would possibly be a price break.

You may also consider the foam insulation used in cold shipping. I used to work in the same building as a medical research company, and a good deal of my 4-inch foam is actually shipping insulation. It looks nearly identical to a flat version of the Auralex foam, and seems to have very similar sound deadening characteristics.

walk away of that. Egg cartons will do nothing but bring junk to your walls. Sound insulayion is not rocket science but it is science. Try youtube. They give valuable information.

My experience was that the egg cartons contributed nothing to the sound isolation, for most was coupled through the rigid perimeters of the wall.

I knew a drummer who lived in a basement of
a private house. He used egg cartons in a corner of his room for his
practice kit. His practice kit was an old drum kit super-stuffed with
pillows and duct-taped drum heads, and duct-taped cymbals to kill off as
much noise as possible so all I heard were thuds and clinks whenever he
practiced. From upstairs, I could hear the faint muffled noise coming
from his room in the basement. The noise wasn't loud, but it was still
noise to me no matter how faint or muffled it was. Being a musician
myself, I didn't mind as long as he practiced within reasonable hours.
And our landlord was a jazz drummer who practiced in a shed out in the
back yard; he hung shag rugs all over his walls inside the shed.

So yeah, anyway, egg cartons offer some sort of sound dampening, but not as effective as more extreme methods.

Egg
cartons work best when used in your immediate area, such as at your
computer desk when you want to listen to music through speakers at close
range, or to absorb sound while speaking into a USB mic for podcasting
and recording software. That's as good as egg cartons get.

Beyond
that, you can be creative and get better results with egg cartons if
you have stack-loads of them. I work in a restaurant, I save egg cartons
now and then for use as acoustic tiles. I layer 3 or 4 cartons stacked
together for thickness and use them as tiles.

Other sound-dampening methods I use are Moving blankets from Harbor Freight Tools.

https://youtu.be/asyu3pvJdy8 this is a great video showing sound deadening. Hate to think about the cost though

I have seen several studios, but thou I can make a room the sounds like one, I have never seen an unfinished wall in one.

Notice here that the egg cartons are used in the room causing the noise! NOT where the noise is an issue. The idea is to decouple the sound from the walls. The egg cartons also reduce echo at the same time (which is probably the main requirement).

Any non uniform surface will help with sound absorption, along with heavy drapes, "pin board", ceiling tiles etc. Rough cork would probably be good, but not smooth or polished cork. Look up "anechoic chamber".

Ideally a practice drum kit should also stand on a decoupled floor to reduce transmission.

I had reasonably good success deadening my basement home theater by lining the walls with Homasote 1/2"x4'x8' boards which i then covered with decorative colored felt using wallpaper paste. Moderate cost.

Greats information for everyone thanks

Cardboard makes good sound-proofing, too [very do-able, and can find it for free]. But there might be some things needed to keep that safe. Mold, Bugs and fire LOVE cardboard!

All three issues, can be vastly reduced, by making a solution of approximately: 1 part Borax + 1 or 2 parts water. Slather that onto all sides of each layer of cardboard, _let dry thoroughly_. Then glue together layers of cardboard to the desired thickness of panel. Then cover the open ends of corrugation using caulk, glue, etc. to prevent critters crawling into the structure to find homes. We covered our "furniture" using contact paper to look nicer than cardboard. Borax captured and left undisturbed, is pretty safe/non-toxic, and is mold, bugs and fire deterrent. The panels can be covered with whatever covering one likes, so they don't look like stacks of cardboard, and make cleaning easy.

I made a bed, clothes storage, seating, for one of our kids, using various stacks and configurations of cardboard. ALSO made 2"+ thick panels to use on the wall that was adjoined to a neighbor's apartment. It's great for reducing sounds, and once properly formed/configured, is very durable....those pieces lasted at least 10 years, and we really had to work hard to destroy it, when the time came. No bugs in it, ever. We did a simple flammability test on ours, like if a candle tipped over on it, or someone tried to use a lighter on it, and had a very very hard time getting it to sustain a flame; it extinguished itself pretty fast.

I learned long ago, that whatever one does to form an irregular surface, can reduce sounds bouncing off hard surfaces. The more irregularities there are, the better. Common cardboard egg cartons [the part the eggs sit in] provide a wonderfully irregular surface, which will help reduce sound waves bounding off otherwise flat walls. Others use foam slabs, similar to what's on old speaker fronts, but thicker.

I imagine that poking a small hole into a drywalled wall, and squirting foam into the wall bays, would do this too. In our experience using various Great Stuff foam in a can products, those usually go into a wall-bay quite irregularly. They do expand [depending on which one, and conditions], but retain a kind of snake-like fold-over irregularity which, in addition to all the air bubbles in the foam itself, those irregular folds also help reduce sound transmission through walls. OR, could use the 2" thick foam panels, score the back and front surfaces to make irregular surface, and bed them into the walls using Great Stuff spray foam.

There are commercially made sound-proofing foam panels with designed-in ribs or other irregular surfaces, which can be mounted on walls, ceilings, etc., to reduce sound transmissions. Some use decorative quilted fabrics to similarly "tune" a room. Could find and recycle foam shipping panels for this, too.

One minor improvement I might suggest is that you can mount the framing without damaging the doorframe and trim, if that's a desirable outcome. Cut the perimeter uprights to length, then cut the top and bottom pieces an eighth of an inch longer than necessary. It will take a little effort to get them in - a mallet or small sledge hammer will help - but at the right length they provide a pressure-fit that won't slip in the doorframe under normal household usage.

This means that, apart from removing caulk or sealant at the edges, you can remove the soundproofing wall panel with no permanent damage. I used to do this during remodels when the goals were mid- but not necessarily long-term, and it worked like a charm.

This is not a solution if security is a consideration, nor if hard impacts to the wall panel are likely, as in a sports environment, or with certain types of dancing.