## Introduction: 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!

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.

I'm wondering about how to create (re-)movable soundproofing, for 2 spots in our house: 1) the door between the master bedroom and the bathroom, and 2) the hallway between the TV room and the rest of the house.

For case 1), I'd like to be able to remove it depending on the current tenant's desires, so it could be up for months at a time. It sounds like your method could work. I'd just need to cut around the baseboard trim to get it to be a snug fit somehow.

For case 2), we need to be able to move it easily, like a door, so that we can just have it blocking while watching TV. I'm wondering about creating a drywall door on a sliding track for that. I can't find evidence that anyone creates "doors" out of drywall, but it seems like it'd be more soundproof than wood. I don't know if being on a track would negate all the benefits of the drywall though, since it's definitely not decoupled. Have you done anything like that?

Thick layers of terry cloth like used in towels makes great soundproofing panels. And you can buy scads of towels at thrift stores for cheap

The Bee Gees used egg cartons when they were kids in their home garage be for they were famous. It does work to some degree but it was a cheap solution that people used 40yrs ago before there where so many break throughs in accoustic batting. Thanks for the great instructable Natalina. I am about to convert a house to dual living and it is my first priority. Does this "Green Glue" have a brand name?

You're welcome! Green Glue is the brand name.

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.

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!

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 heard [many yrs. ago] about the sound absorption of cork, as well. good idea!

Look at soundown.com for foam/lead sandwich sound deadening sheets. Worked well on boats when I was in the marine industry. Also has lots of general info on sound control.

AMAZING

Soundproofing in a full range of 200 to 20.000 Hz is a task of professional attitude. Low frequency sound is to be insulated with solid-weight materials with weight of approximately 250 kg/m2. High frequency sound is to be insulated with light-weight materials (like mineral wool etc.) Composing the partition wall should never be symmetrical because of resonance.

Well, I can tell you what I did and it worked 100%. My bedroom wall was on the other side of the TV in the living room.When I had to replace the drywall in the bedroom, all the walls, outer as well as inner except for the closet wall, got solid foam 5" or so thick roof insulation boards cut and stuffed in tightly between the studs. Used broken pieces near the top as well. 1/2" drywall added over it and the room was silent even with the TV blaring! The only "hard" work was cutting the thick insulation boards to fit, and then tapping them in with a rubber mallet flush to my side at the studs.

Also, noise barriers like these can be a quick solution when it comes to reducing noise. You can put them up quickly, and this doesn't require much additional work besides assembling a simple metal frame and then attaching the barriers to it. Their industrial grade quality will ensure a very good soundproofing.

nice soundproof info & tehnique

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This is awesome!

Several other things to consider include what frequencies you are trying to mitigate. Speech falls in a certain range (300Hz-3.4KHz) where music can go lower. Low end frequencies are the hardest to mitigate as often they transfer through the structure (walls, ceiling, floor) and can be hard to decouple without great expense. High frequencies are very directional and can often be stopped through mass. Watch out for what we call flanking paths such as windows, transfer grilles or other HVAC duct work in either common walls or run along the same path as sound (like water) finds the path of least resistance and no amount of stud walls or insulation will alleviate the problem. Also, make sure there are no electrical outlets that are back to back in the common wall as this might as well be a hole in the wall. I would also recommend putting a layer of rubber or foam around the framing sides to decouple the new stud wall from the existing structure otherwise you may wind up with a bass drum effect amplifying low end frequencies.

Raymond Kent
Managing Principal
Sustainable Technologies Group, LLC
Acoustics, AV, Lighting, IT Consulting

my neighbours have booming voices and love to use them, as well as power tools sometimes into the evening. I am not allowed to confront them as I am prone to want to exercise my clenched hands. The room in question is party to my 5 year old bedroom. I decided to dot and dab a15mm DB plasterboard and covered that in rolls of 6mm cork, thinking this would help. It hasn't . Have I exacerbated the situation with the dot n dab? I'm considering removing it, applying rubber sheet/dense foam and plasterboarding that? I'm in construction and have a reasonable product knowledge but this has stumped me. Any knowledgeable help appreciated !

I've never used dot n dab so I can't speak to it, I can only speak to what I built which has performed well for me. Adding a layer of green glue before the plasterboard would help, in my research that was the product which helped the most out of all the layers of insulation/drywall etc. There are also a lot of great suggestions in the comments from people more knowledgeable than me, definitely worth a read. Good luck!

Old mattresses as well (used one against window when Hotel right in back had a machine that sqealed all day and night and each Hotel would say it was the other Hotel's machine. Then it caught on fire and that took care of that. Was amazed (due to all the stuffing I suppose at how the mattress stopped all the noise. (dreamed up lining apartment with them, lol)

Oh the pain!!! Lived in NYC when at the time 79 - 2012, one had to have rubber matting and a carpet on top. Rubber is the best product for vibration. Then a fire, and the new management did not enforce this law. Nightmare began. I did huge amounts of research when the person upstairs used to lift weights and drop them day and night, day and night - almost went insane. Because it is a vibration and cinder block walls, sub flooring cement, and wood floors the "box" called my unit was like the inside of a drum. Management did nothing but even the police (who asked to sit in our apt) were stunned. I ended up sleeping on the lobby couch. The walls would shake and even frames fall off. My cat would circle around and around looking up at the ceiling!!! BAMM! (out of the blue). Former singer (used to pad closet with blankets and sing in there when people were home, even put pillow over mouth (no one wants to hear opera trills, but sang blues/jazz). Best is to be able to rent a professional studio.

My brother was an architect and told me after I told him I planned to build a "floating" box to at least sleep in - it would be cost prohibitive. Noise pollution is one of the main reasons for suicide!!! (sleep deprivation).

But I remember in the "old" New York, rubber matting was used and could easily be bought at any carpet outlet. Foam is almost useless. I remember one guy in an earlier apartment using it with a carpet on top against one wall.

Lol, this person also told me another nifty trick. If one hears someones music and they don't care - play Chinese Opera... I told that to a person who picked up my rescue pacu fish when she told me they had a similar problem and later when picking up other rescue fish I asked how it went. Her husband parked their car out the window of said noise maker and played it all night long (let other neighbors who had complained as well this would be done). Never heard a peep again! (nothing against Chinese Opera but 1/4 tones on high tones - well most can't listen to it for long).

http://www.rubberflooringexperts.com/exercise-fitn...

Good luck.

wrapping studs with foam sill seal and insulating cavities w/ Roxul soundproofing insulation, and sealing with green glue is economical and fast..need to knock it down further? build a second wall with 4" of dead air space between the two..employing two layers of sill seal between all mated surfaces..walls should be hung from the ceiling and 'caulked' top and bottom with sill seal..rough pegboard is preferable to sheetrock and doubles as a functional wall as well..then, you can turn up to 11

He's trying to reduce the volume of telephone calls, not trying to isolate a Heavy Metal Band. Cost is a consideration as well. Hanging moving pads or carpet is a low cost way to reduce some volume.

why didn't you remove the door??

yup, this stuff:

http://www.bondedlogic.com/ultratouch-denim-insula...

I installed some under the floor of the media room in my old house (MBR below) and it helped out quite a bit! Managed to cram 4 bags of the stuff in a lexus ;)

Hi

A couple of notes. Very good article. You can improve on the isolation by using two different thickness drywall sheets. The 5/8" and a 1/2" would work better than two 5/8" sheets as the have different mechanical resonance frequencies, thereby passing and or blocking different frequencies.

The green glue is amazing. Roxul Safe and Sound would work better than regular insulation.

For ceilings, it would work well. I just did my basement ceilings. Filled joists with two layers of Safe and Sound, then drywall. Worked well.

Even better, though I didn't do on this house as I plan to move, would be to us RSIC clips to completely isolate drywall by hanging it.

Of course if you used 5/8" on one side and 2 x 1/2" glued together on the other side of a decoupled wall (staggered studs are best) then, as you said, the two sides would pass different frequencies etc.

Used staggered wall studs and drywall about 25 years ago in my office with no perimeter isolation of the drywall and found that I could not hear the adjacent office sounds at all. Used 5/8 drywall on both walls that were disconnected from opposite wall supporting studs, but not from their end walls and not from the ceiling. Their supporting sill plates were on concrete.

Egg cartons, corrugated foam, Sonnex, and other such products are simply methods of controlling internal acoustics that all fall under the term of "Reflections".

Diffusion and absorption of reflections in a well designed and installed space will give the user a room free of flutter echo, nodes and anti-nodes, and distracting secondary reflections.

These methods of acoustic control do little or nothing in respect to isolation of noise, and materials like egg crates, both in paper and foam are a deadly fire hazard!

Typical floor construction when design of the existing structure will allow would be something such as this...

2x6 Joist 16" O.C. with 2x2 inch squares of 3/4" thick 70 durometer neoprene rubber at every intersect, and every 16", cats are placed as you would in any standard layup.

Wiring chases are set below this structure if possible in 4" and 6" EMT pipe and cabling is installed prior to floor installation with numerous pulls (rope to pull additional cabling) for future wiring.

A sheet of 20 mil plastic is laid over the joist work and tucked down into every bay, and the structure is filled with sand.

The first layer of substrate is 1/2" plywood screwed and glued with PL, then 5/8" rock, 1/4" Masonite, 3/8" greenboard, 3/4" ply and then your flooring, which if oak should be white oak laid on a moisture barrier membrane.

This helps with movement and noise during seasonal changes, which should be minimal.

A floor with this kind of mass and resonant differential in the substrate absorbs tremendous energy.

You can stand 10 feet away from someone and stomp your feet as hard as you want, or stand near the drum kit and feel absolutely nothing in stocking feet.

If sound is to be isolated from a structure below, the walls are of great concern for conduction since these may be homogenous to the entire structure.

Once this has been addressed, a dropped ceiling isolated from the internal walls of the structure below is the way to go.

The gap is sealed with flexible caulk as air is the mode of transmission at this point of entry.

Denshield and rockwool products are excellent for absorbing sound here, and using Resilient Channel and clips to decouple the Denshield is the trick these days.

Depending on how high the SPLs, you may need more layers of differing thickness and varied substrates.

Look at STC (Sound Transmission Coefficient) ratings, of each product VS budget constraints.

The lower the STC the better, as this is the amount of transferrence.

Best of luck to future noise sufferers!

I think this covers it pretty well, but, please, where this is critical, consult with an acoustics engineer who also understands that the mass of the wall itself needs to be supported on that appropriately compressed rubber or composite damping material. The durometer of the rubber chosen could be varied, depending on load per unit area of the isolation pads. There are also composite pads just for this purpose. Sonnex materials and its competition materials are expensive per unit area, and the acoustics engineer could help with placement of that material class, as well. Best used on large radiating surfaces.

I have a friend who is a piano teacher and she 'wallpapered' her piano room with egg boxes which reduced the transmission of sound dramatically apparently.

Another good sound (and vibration) absorber is cork (according to a National geographic mag I read donkeys years ago). Hope these ideas help all the sound proofers out there.

I did that to dampen noise from a neighbor's garage band about 40+ years ago, and, of course, it was only useful for what came through that area of the wall, not useful for what came under and around the door or was conducted by the door frame.

The wall is not necessarily the problem when it comes to low frequency sound. These sound waves will travel through the floor. Here the same principles governing stereo sound systems come into play. Our ears will denote different sounds coming from separate locations only when they are in the high or mid ranges, so for these frequencies multiple speakers in different parts of a room make sense. And these speakers, to be most effective should be placed on a level with our ears. For base sounds, however, it's a different story. Doesn't matter how many speakers you have, the waves are too big to hear any separation. So for base, you only need one speaker, and the most effective placement is to direct it squarely at the floor. So to truly soundproof a room when music is concerned, unless you are on a concrete slab, you also need to separate the floor somehow.

You could go higher-tech more cheaply, perhaps, and use noise-cancelling electronics, i.e. a speaker /voice coil and your choice of driven surfaces. A mic attached to the floor inside the room would give you the signal you'd want to cancel. This is not new science, so you should be able to find suitable circuitry on a hobbyist website or might even be able to find a cheap low frequency / audio frequency unit already on the market. You'd likely not care about any effectiveness below about 20-16 Hz, so could cut costs by not trying to go near d.c., unless there were furnishings in the room that tended to vibrate at first harmonic of low frequency vibrations, therefore rattling. If none of that is already noticed, then no need to isolate the furniture.

how about in europe, where most walls are made out of bricks or concrete? The "improvements" are good for american woden houses, but here in europe, the walls are solid, i'd love to see a instrucabel of how to soundproof those.

brick and stone houses should be easier to soundproof. Just use deadener btn the outside and the inside wall.

I've heard of audiophiles using 1-2 layers of mdf board in their living room or den to keep the walls from resonating.

What audiophiles do to reduce sound input is sometimes entertaining, and sometimes rather ineffective. Also, what some audiophiles do to reduce electronic noise, i.e. going entirely analogue, including motor drives is often humorous when considering what these guys imagine that they can sense.

I have seen more than one solution to this, with respect to the double thickness of materials, and one includes an adhesive sandwich that includes a damping adhesive bonding layer between the two wall layers that were isolated from the studs. Additionally, I have seen 5/8 or 3/4 fiberboard semi-floated between the walls, that is, not nailed to the studs, but sitting on compliant material and having the complete perimeter, but not the face, stuffed with fiberglass insulation. I suspect that it would have been better if the fiber board floating component had been suspended with conventional R11-R13 paper-faced fiberglass stapled across the whole space from perimeter studs, top to bottom and side to side of the rectangle. I'm happy no longer to live where this is of any concern to my daily life. There are many composite materials on the market that are available in large tile form and are designed to reduce transmission of vibrations. One thing to remember about them is that they tend to work best under a particular range of load per unit of area (lbs/sq foot) of tile, and that they can actually transmit too much is insufficiently loaded. This makes them a bit difficult to use in vertical planes to isolate walls, for without having a good metric for their compression, they are likely to be less effectively used.

I'm a bit confused, or did I miss something here? Did you just seal up the entrance to the room? If so, how do you come and go?