I'm assuming the walls are wood stud walls with drywall cover. 1 - An extra layer of 5/8" drywall applied to each side of the wall will improve the STC (sound transmission class) by about 30%. 2 - Add metal resilient furring channel at 24" o/c over the existing drywall on each side of the wall and then cover with 5/8" drywall to improve the STC by about 45%. 3 - If you don't mind removing the existing drywall on one side, you can put 1.5" fiberglass insulation between the studs and then cover with two layers of 5/8" drywall to improve the STC by about 60%. 4 - Same as #3, but add resilient furring channels between the layers of drywall to improve the STC by about 94%. 5 - Build new walls inside the existing walls. Use 2x4 studs at 16" o/c, 3.5" fiberglass insulation, two layers of 5/8" drywall with resilient furring channel between them. This will improve the STC by about 100%. This information comes from Architectural Graphic Standards, 9th Ed. Get this book from your local library if you want additional info on soundproofing floors and ceilings.

What's often being done and seems to work pretty well is to glue empty egg boxes to the wall. Here's a page with some information about the process and other ideas: http://www.airo.co.uk/garage.htm

Sound will bounce on sturdy surfaces, it will be best for itself if it is flat, as it will not spread and thus weaken. So instead of putting a citadel barricade for it to never get through, how about neutralizing it? Professional record studios use a spongy, "thorned" material on the walls to kill echo. The softness absorbs the vibration of the soundwave and its shape spreads whatever remnants into smaller chunks only to impact nearby soft material. It works pretty much the same for not wanting anyone to hear you from outside, sound won't travel through. You'd want a soft and irregular (spread nearly randomic) surface, and since there is nothing cheaper than free, how about covering your walls (every corner, every spot) with a soft, irregular spread, free material? Plants. But not just any plant. Moss would work better. To get an idea, search the web for photos of "Peat Moss", so you can picture what I'm talking about. You'd want like 2 to 3 inches of moss to absorb the soundwave shock and spread it over itself. Some moss take ages to grow over a place, some take much more less and spread wildly, it depends on the variety. They like porous surfaces like rocks, brick, plaster, etc. But that I leave to your imagination and budget. Or you could try regular plants, but you'd need lots and lots to achieve the required density.

The most inexpensive way I can think of is to use plenty of old clothes and old blankets. You can find old clothes very cheaply at yard sales, thrift stores, etc. (less than $1 an item) Hang all of the clothes on the walls from floor to ceiling using 2 rows of coat hooks, (at the 8ft level and the 4 ft level) about 3 or 4 layers deep. Then cover everything with old blankets so the room does not look like a closet. So much sound will be absorbed that you could scream your lungs out and not be heard. If you have ever been in a carpet store where they have the rolls lined up on both sides of an aisle or in a fabric store that is arranged the same way, you will notice how the sound is so "dead" as its absorbed making it a bit more difficult for you to hear yourself talk.

Don't forget to carpet the floor and use acoustical tiles on the ceiling, a suspended ceiling using acoustic panels would be even better. If you don't mind the room looking like a small radio station you can put acoustic tile on the walls. But.. are you trying to keep sound in or out? Most of the ideas given are for keeping sound in , they will work to keep sound out but will work better if applied to the outside or sound producing side of the walls. You'll become a tourist destination, "See the house that wears old clothes!" On an exterior wall plants such as dense evergreens like cedars and arbor vitae or tall boxwood hedges will help. Use double or more glazed windows and storm windows. I really like Jack Scotty's miserly, er, frugal, approach, you can buy cloth batting used for blankets and comforters and hang that instead of old clothes or use tapestry or heavy curtains instead of blankets but you'll miss out on the possibility of finding forgotten change in the pockets of the old clothes. Instead of rows of hooks just use nails or stretch 3 or 4 ropes from wall to wall with hooks spaced along to prevent sagging. And why use old clothes? If you use curtains that you can slide open, you can hang your real clothes back there and have a giant live in closet. You'll have to twist the hooks of the hangers so the clothes hang along the wall or just drape old ones over the ropes. Lucas' egg carton idea is also cheap. Back in the days when The Bensley Trio Two was the star attraction at Madison Square Garage we used something similar to line the walls of the garage. ( For some reason neither the parents of the band who owned the garage nor the neighbors appreciated the free concerts.) We used the styro-foam packing inserts that come with small appliances, cameras, brand new real loud amps, etc. They usually have a flat surface and can be glued to the walls. We painted them with different day-glo paints so they looked far out, man, under black light, but you can try some more muted tones, it does look like a piece of wall art. We found a lot in the dumpsters behind the stores that sell such things. Encyclopedia has good suggestions for more efficiency, of course they are more expensive, but you do wind up with a more "normal" looking room.. Instead of using fiberglass insulation though, there are open celled styro-foam panels that do a better job of sound insulation, just make sure they have the proper fire ratings. Notice the references to "resilient: furring." The majority of sound transfer from one room to another actually takes place in the structure of the wall itself and not the air inside it. Sound wave travels through air, hits drywall, transfers to studs, transfers to drywall on other side then to air. The resilient furring is between the drywall and stud. Idea #5 is probably the most efficient but you lose 4" or more of space on each wall, you don't want the new wall to touch the existing wall so there will be a gap between them. There is an easier method that works almost as well as the room within a room and one that I have used successfully. It would be idea "41/2" I guess. Strip off the drywall from which ever side is easier to work with.( If it is a plaster wall that's a bunch of work.) Put your sound insulation in there between the studs, it would be best if the insulation is under 31/2" thick so it does not quite reach the new open edge of the studs. . Run 1X3's from ceiling to floor spaced halfway between the existing studs, you don't want these strips to touch the insulation. Fasten them to the face or edge of the wall's plate and sill, they will be "outside" the wall making the wall 3/4 " thicker. Nail 1X2 strips along the sill and plate between the new vertical strips. For 'resilient furring' use the foam weather stripping with the sticky back, get the stiffest hardest foam you can. run it all along the top, bottom, and ends and down the new verticals, use a double row at the new dry wall joints. fasten the new drywall with screws and try not to compress the foam too much. It's tedious and persnickity but not difficult. The new wall will be kind of springy, and if it gets much banging the joints may show cracks,for more stiffness use 2 by material turned flat instead of 1 by's. If you are a carpenter turn them edgewise and toe nail them in with that gap between them and the back wall. Use a heavy texture on the wall before painting. But. I really like Jamiroquai's idea. ( Jam , all these ideas are "absorbing" or "nuetralizing" and not "citadels".) You can buy all kinds of moss, Scottish, Irish, Canadian, etc etc. I'm gonna gouge holes in my walls pour potting soil in there, stuff moss between the chair cushions. Install a sprinkler system. Gnomes, fairies, and trolls will rent space from me. This is gonna be so fine! And then...What? .. Say again. ..Huh?...I can't hear you. I said ..I CAN'T...neva mind. Hmmm gettin kinda spooky in here, can't hear a thing...

Odd-size blocks of foam, some not small, are frequently available in places (like futon stores) that use and cut a lot of foam. If possible, glue in preference to nailing -- the nail, which is solid, transmits vibration into the wall, which is what you're trying to avoid. Incidentally, if you're an instrumentalist, there are shaped foam tubes that will hold most wind instruments (there are holes for the mouthpiece end, slits for hands, etc.). Lot cheaper than doing a room. If you're an organist, good luck.

Soundproof the room by carpeting the walls. Not only can you find inexpensive carpeting at a carpet remnant store, but, the finished product looks rather nice.

If the room is not build yet,(the studs are still visible where you see through the walls) you will save the most money when soundproofing. But if it is, there are some good answers posted before mine. If you are soundproofing for listening to music, "Bose" makes noise canceling headphones for consumers.

Here's a good one. when we purchased our house a few years ago, the previous ownver had a sound studio down below divided up into sections. That would have to be pretty sound proof! When we decided to do some renovations down there we went to remove the walls and what did we find - dirt!! The cavity (of about 4") was packed with just normal dirt from the garden. This guy actually produced sound tracks and recordings down there so i can only assume that it worked. There is nothing around much cheaper than dirt!

As can be seen by the many answers, there are many things that can be done to soundproof a room or make much quieter than it is already. If you have the luxury of building the room from scratch, rather than converting an existing room, there are some construction methods that will help. A wall is normally constructed using a 2x4 attached to the floor which supports 2x4 studs, spaced at 16-inch intervals, and capped with another 2x4. The wallboard panels on either side of the wall are attached to the same studs. This increases acoustic transmissibility. If you use a 2x8 base, for example, with 2x4 vertical studs, you can stagger the studs at 8-inch intervals, every second stud meeting the inside edge of the base (e.g., studs 1, 3, 5, etc.) and the remaining studs meeting the outside edge (e.g., studs 2, 4, 6, etc.). The studs on either side of the base have the required 16-inch spacing. This wall is capped with another 2x8. When the wallboard is installed, there is no direct connection through the wall since the wallboard panels on either side of the wall are attached to different studs. There is a direct connection at the base and cap and around windows and doors, but the transmissibility has been reduced by a substantial amount. The cavity in the wall should be filled with 4-inch fibreglass insulation, woven between the studs before the wallboard is installed. The wallboard should be fairly thick to reduce vibration. It is better to use two layers of wallboard, rather than one. The second panel should be covered with an adhesive before being screwed in place, to ensure that it is tightly bonded to the other panel to stiffen the wall. The joints in the two layers of wallboard should be staggered. Use 5/8-inch wallboard rather than the 1/2 inch wallboard normally used for walls. Similarly, a drop ceiling with acoustic tile and a 4-inch layer of fibreglass insulation in the cavity above reduces acoustic transmissibility to the structure of the home and/or the floor above. If you install a drop ceiling that uses L-brackets for support on the walls and T-brackets suspended from wire hangers and the L-brackets, you may find the fibreboard tiles vibrate against the Ts and Ls and produce noise. The supporting edges of the T- and L-brackets can be lined with foam insulation tape to reduce this problem. Alternately, ceiling panels made from fibreglass panels which have been bonded to a vinyl sheet on one side can be used. These panels do not bounce like the fibreboard ones do. If the room is in the basement on a concrete floor, there will be some transmission of sound to other rooms, but much less than if the room has a raised floor or is on another floor of the house. A concrete pad overlaid with industrial low-pile carpeting makes a good floor. I have used egg carton walls before and they work well, but only at higher frequencies. They don't look that great, either. Hanging heavy fabric in front of the walls will help absorb some of the sound. If the fabric folds back and forth on itself like drapes that are partially opened, the effect will be improved. You can also fabricate acoustic panels using a stiffened wooden frame a couple of inches thick, attaching heavy fabric to both sides, and filling the interior with fibreglass insulation. These panels can stand on their own base or hung from hooks in the ceiling and arranged as required. They could also be attached to the walls and door. Such panels are available commercially, but they are not cheap. Professional anechoic chambers use acoustic foam wedges that are attached to the walls, floor, and ceiling with the points facing into the room. These may be several feet in length. The floor is usually steel mesh that is supported on posts and steel members and is, effectively, acoustically transparent. However, one would not want to use an anechoic chamber for anything other than acoustic tests, because they are a very 'dead' environment.

resonant channel, go to the library and look for books on your subject.

for informational purposes only.It takes 2 inch foam on every inch of the room.Then you apply drivet.Its a fiberglass mesh and a type of concrete/glue.Apply this over the foam and your room is soundproof and smellproof.

Be careful to distinguish between soundproofing and acoustics. Soundproofing materials are generally heavy, flexible materials like vinyl barriers, or, they use some method of reducing structural vibrations. Resilient channel and more sophisticated channel products like isoTRAX are examples of products designed to reduce structural noise. Acoustic materials like foams, most ceiling tiles, compressed fiberglass panels and other high noise reduction coefficient materials are designed to improve acoustics by reducing echo and reverberation. They do not block noise. There are some composites, however, that use foams to decouple vibrations between barriers and machine and engine enclosures. There are several companies that offer good advice and you can find these in the Internet. It's a good idea to be prepared with specific applications, since there are so many situations that require different approaches. There is also a lot of nonsense out there. Egg cartons will not and never have been used as soundproofing materials. They can be used to diffuse noise in studios to reduce standing waves but they won't block any noise.

Make everyone else deaf