Build a Soundproof Wall

Intro: Build a Soundproof Wall

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!

Comments

[skytraxx]

Very nice job! Do you own or rent?

[morrow.max]

Use "Safe N' Sound" Insulation. They sell it at Lowes.

[Mattcais3]

Some of the ideas here- while excellent seem to be geared to a more professional setting like a recording studio or the headquarters of the NSA.(lol)
You’ve done a great job closing the door shaped hole in the wall and as you said, there has been a noticeable reduction in sound pollution.
May I make a simple suggestion for a further add-on which may help cut down even more sound but won’t require any more major construction?
You’ve probably been to a theatre or music venue and seen the huge thick red velvet looking curtains they have hanging in front of the stage. These are usually backed by a second curtain of heavy black felt like material hanging a few inches behind the red one (Air being a great sound proofer makes this gap make a lot more sense to me now). These heavy curtains are not only meant to stop the audience from seeing what’s going on before the show starts but also to stop them from hearing set changes, scraping scenery, shuffling feet, whispered conversations between musicians/actors etc. It works pretty well and I’ve always hung the thickest curtains I could find in every home studio I’ve had to great effect. (Possibly the ripples of the hanging cloth help to diffuse sound as well, in a similar way to the old School eggbox idea?) you could simply mount a curtain rod at the top that extends beyond the door frame a few inches on either side & hang the thickest curtain material you can find ( I have found that old community theatres often have old curtains stored below the stage, gathering dust, that they will gladly let you have you take off their hands - this is the best kind) and hey presto! A not too ugly, extra layer of sound baffling at a low cost.

[Natalina]

Great idea. I've definitely been surprised at how much a heavy curtain can do, and that's an interesting note with theaters having the air gap. Makes sense considering it's the same principles as a decoupled wall. Thanks for the tip!

[chuckyd]

The attached image shows an addition to your plan to effect a significant improvement. There is one condition, though. The resilient channels are to be placed on the side with the noise. In your case, apparently, there is noise generated on both sides. In that case I would mirror the double layers of gyp with the resilient channels to the other side of the studs.

[Natalina]

Thanks for attaching this image. The resilient channels sounds like a good addition.

[charleszcy]

Instead of using 2 sheets of the thickest drywall, use 2 sheets of different thickness. That way the natural resonant frequency of one sheet is damped by the other. A sheet of peg board with holes of different sizes creates a "helmholtz resonator" which can trap noise.

[Natalina]

Super interesting, thanks for the tip.

[ThreeEyedWilly]

My father was the owner of a music studio back during the 1950's and 1960's. We had about a dozen teachers of various instruments in rooms roughly 6 feet by 8 feet. To reduce sound transmission between the rooms, we used decoupled walls. Since the walls were not load bearing, this was not a problem. The way it worked was very simple. There were basically 2 sets of studs on each wall. One set of studs was offset about an inch or so from the other, alternating as you went along the wall. The drywall was attached to the studs. There was very little sound transmission from one studio room to another. You don't have to use 2 by 4 studs to do this. Use 2 by 2's. Set them a few inches apart, and run a set of studs for each side of the wall.

[AndrewSVaz]

I've always disliked fibergalss. I use expansive foam for this kind of instalation. To keep the insects away I use neem oil on it (after the expansive foam is dry...).

[FlorinJ]

Foam is light. It will not properly keep noise out.

Fiberglass is somewhat heavier, but still pretty light.Heavy rubber mat, or dry sand would work greatly.

[bgreen3]

This is an excellently written guide. Well done!

[greatblue22]

You just spent a fortune of soundproofing one wall.

[kmpres]

Nice instructable. I may apply some version of it in my next house if I find the noise coming in from outside is unbearable. Another tip for new house construction I heard over the internet is to make the outer walls of the house two inches thicker than what the studs and opposing drywall sheets would add up to. You then stagger the studs in a zig-zag pattern so the drywall on one side is nailed only to the even studs and the drywall on the other side is nailed only to the odd studs, then fill the space with as much insulation/sound-deadening material as you can fit. This decouples the wall surfaces and makes a kind of pleated but undivided dead-air space between them and also reduces conduction through the studs because each stud touches only one drywall surface. They cannot conduct sound to the other side because they don't touch the other side. For the same reason it also makes a better thermal barrier for heat retention.

You and your readers could now help me with a sound-deadening problem I've been wrestling with. Seems my new shop vac is loud enough to cause avalanches, earthquakes, hair loss and migraines, oh, and hearing loss as well. I need to fit it inside some kind of sound-deadening enclosure so I can use it and still preserve my hearing for a happy, sound-filled retirement. It needs to be light, movable and somewhat form-fitting. Any ideas?

[chuckyd]

I designed a noise reducing wall for our woodworkers' guild according to the attached sketch. There is also a door in one of the walls. The door is a metal door with sound insulation and weatherstrip gasketing all around. There is an automatic drop sill at the bottom of the door. The metal door frame is filled with insulation. There are two 15hp dust collectors in the room, and normal conversation can easily be carried on just outside the room.
It could have been made even better with two types of improvements:

1. Find a way to reduce noise in the duct work as is passes through the wall without impeding airflow.

2. Look at the connected equipment to reduce noise at the intake. We found that the loudest sound of the system was the air entering the duct work through the 24" planer. The area of that opening is apparently smaller than the area of the duct attached to it.

[ringgoldst]

Re: shop vac. Get a long hose. Put it in another room.

[JohnR245]

I have considering the shell-construction of net-zero (passive-house) building and the staggered-stud is used a lot. Seems very expensive& hoping to find better performance at a lower cost. Seen some interesting SIP (structured panel) but IDK - open to ideas

IDK what your vacuum is made of but suspect if it's that noisy it's probably best/cheaper just to replace it. I have a Rigid shop-vac that is both (pretty) quiet and powerful as well as light & durable - I paid ~50USD on sale

If you really want to keep it I'd fist look at where the noise is coming from. The roar from air-flow usually needs an expansion chamber (muffler) If it's a screech prob bushings/bearings need replacing. If there's some metal it could be 'singing' & need dampening,

[RussS29]

SIP formed concrete construction is *solid* as heck and is good both thermally and sound-wise. If I was building brand-new, that is exactly what I would use.

[RussS29]

I would be cautious of trying to shroud your shop-vac in the way you are describing, as air-flow is required both for operation and for cooling.

[simsamurai]

As a former remodeling contractor I can suggest several key items and tips for drywall. Also take note that the big orange and blue box stores sell a cotton / denim based sound insulation that is much better than standard fiberglass wall insulation.

First, use a good level, one that's at least 24" to 36" wide to first determine the highest side / corner of the area that you are wanting to fill.

Second, use an angle finder gauge (8" to 12") to determine your starting corner's first two angles, one vertical / one horizontal angle and then transfer them over to the drywall sheet and slightly adjust your cut lines up / down on the sheet as needed. You will quickly see that even though things may visually appear flat, level, 90-degrees, etc, they are ALWAYS not level and are usually off by 1 to 5 degrees or more. Therefore over a 3 or 6 or 8 foot length you will quickly see how cutting "square" drywall lines without first accounting for these small angular differences can and will leave huge gaps on the opposite end of your cut line once you set the sheet in place. This is the #1 biggest mistake people make. It's also a good idea to cut all lines at least 1/16" inward to leave a little wiggle room, especially when being this precise with angle cuts.

Third, once you determine the starting corner, measure everything from that same point of reference "up and over" for the sheet you are cutting. For example; lets say you need to cut a hole for an electrical box. Measure up "x" distance with a level to make an exact vertical line, then over "x" distance with the level again to the top left (or top right) of the box you need to cut. I always set the tops of outlet receptacle boxes at 16" (level) and tops of light switch boxes at 48" (level). So this way, if you instead set and install all of your drywall sheets horizontally rather that vertically, it makes it much easier to cut out the light switch boxes (as the box tops are now on that 48" seam) and secondly, you create a single central seam on the wall to mud rather than a bunch of 96" tall vertical seams every 4ft apart.

Also think about your body movement of just mudding a single horizontal line at 48" vs having to fill a bunch of seams from floor to ceiling. The constant up / down will quickly wear out your knees and back. For example, in a 12 ft wide room you could hang just two 12ft sheets horizontally as opposed to 3 sheets vertically. The horizontal mud line is 12 ft (plus side corners and ceiling) but the 3 vertical sheets yield 16ft of mud/tape line seams (plus corners and ceiling). You can do the math on the time/materials savings for a whole room. If doing 4 walls it saves an extra 16ft of mudding/sanding!

You'll also notice that because wood 2x4 wall studs are rarely strait and vertical it is often very difficult to have the vertical seam of two sheets share the same stud as they each only have 3/4" to bite onto. And if the stud is bowed or curved then it quickly gets much worse.

So again, by always setting drywall sheets horizontal wherever possible you will instantly overcome a great deal of time and hassles in both screwing it in as well during mudding, sanding, and painting.