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Home Tech - Soundproofing Room Within A Room
Room Within A Room

 In the simplest terms, sound is waves of energy travelling through the air, just like waves of water on the ocean.  In fact, think for a moment what life would be like if sound WERE water waves.  Your drums, then, would be like a wave generator, slopping water everywhere.  Let’s say you’re playing in your bedroom.  Think of every way that water could escape…through cracks in the floor, electrical outlets, vents, windows, doors, etc.

Sound is escaping the same way.  But sound is even worse!I’m not a pro.  I’m writing this as an amateur’s starting point to soundproofing.  That means even though I try to be accurate and give good advice, I may have made mistakes, and I might just be plain wrong about things.  Also, this information may be out of date by the time you read it.  Construction is dangerous, and there are countless ways to get injured, not achieve your goals, and lose money in the process.  I urge you to engage a licensed contractor for work of this type.  This FAQ represents my educated OPINION, but is not presented as FACT.  Proceed entirely at your own risk.

Disclaimer 

I’m not a pro.  I’m writing this as an amateur’s starting point to soundproofing.  That means even though I try to be accurate and give good advice, I may have made mistakes, and I might just be plain wrong about things.  Also, this information may be out of date by the time you read it.  Construction is dangerous, and there are countless ways to get injured, not achieve your goals, and lose money in the process.  I urge you to engage a licensed contractor for work of this type.  This FAQ represents my educated OPINION, but is not presented as FACT.  Proceed entirely at your own risk.

 

I (Craig) am not responsible for any damages of any kind connected in any way with anything written herein.  If you do not agree to this, PLEASE do NOT read on.  By reading on, you agree to indemnify me against any and all penalties, damages, losses, etc. related in any way to anything written herein.

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When sound waves hit structural components like floors and walls, the energy vibrates the wall.  The wall, in turn, creates a new wave on the other side.  Drywall, which is pretty flexible, is really good at this.  Your walls, in other words, are really big drums you didn’t even know you had.

Bass sound waves are especially nasty.  Bass waves will penetrate easier than other sound waves, and they will carry much further.  Think about when you walk past a dance club at night.  Chances are most of what you hear is the thumping of the bass.

So…what can we do?

 How Does Soundproofing Work?

There are two things that stop sound: air space, and mass.

Sound attenuates, or loses energy, as it travels through the air, just as the ripple from a rock thrown in a pond will grow smaller and smaller as it radiates outwards through the water.

Similarly, when sound hits something solid, it has to expend some of its energy to vibrate the mass.  When we combine air space and mass, we get really good soundproofing.

Therefore, when soundproofing a room, the ideal situation is to build a “room within a room.”  You play your drums, the sound hits the walls (mass), then is forced to recreate new waves in more air space (the gap between the inner room and the outer room), then hits another wall (more mass).  By the time it gets out of there, it’s lost a lot of energy.

What About All This Foam I Bought? 

There is a big difference between BLOCKING sound and ABSORBING SOUND.  Sound absorption is used to stop the reflection of sound in a room (echo, rever beration, standing waves…that’s a whole ‘nother topic).  This stuff is crucial for maintaining a good acoustic environment inside the room.  Typical products include Auralex and Sonex.  Commercial products include so-called “acoustical tiling.”   However, while these products keep sound from bouncing back at you, they DO NOTHING to stop sound from passing through!!!

Just in case you missed it:  acoustic foam products DO NOTHING for soundproofing.  That’s not their job.

Makes sense, right?  If the sound isn’t coming back at you, it’s got to go somewhere!  In fact, products like Auralex actually transmit sound waves better than most other materials.  Never be fooled into thinking these products will soundproof a room.

How Do I Measure Soundproofing?

Soundproofing is measured in a variety of ways, but the most useful is the STC, or Sound Transmission Class.  The STC rating of a particular construction component will tell you roughly how many decibels that component can stop.  A typical room with single-stud drywall construction and a wooden door probably has an STC range of about 20.  That means when you’re playing your kit at typical levels of 100+dB, anyone outside the room is getting at least 80dB, which is damn loud.  Mind you, that’s assuming the room is AIRTIGHT.  But it’s not.   That knocks about 5-10 STC points off of your rating.  Now, your kit is heard at 85-90dB.  You might as well not have any walls up at all.

 This is a big point.  Soundproofing is one of those things you can’t do halfway.  If you can still hear those drums, your “mostly soundproof” room isn’t soundproof at all.

Get a digital dB meter from Radio Shack.  It costs about $50, and it will help you determine your soundproofing goals.  For instance, if you’re soundproofing a garage so the neighbors won’t hear, and the ambient noise in your neighborhood is 60 dB, a total STC of 40 to 50 should do the trick.

For various STC ratings, see: http://www.lis.net.au/~johnsay/Acoustics/Pages/STC%20Chart.htm

 Okay, enough.  HOW DO I SOUNDPROOF MY ROOM?

Let’s start with the single biggest job.  The walls.  The kind of walls I’m about to describe certainly apply to the construction of a room within a room (RWAW), but you can use the same concepts to enhance a pre-existing wall if you’d like.

Firstly, we want to create that essential AIR SPACE.  I recommend that there be a six inch gap between your pre-existing wall and the RWAW.  Less than that reduces the soundproofing, and more than that hasn’t been shown to increase it.  Remember, when planning your room, you’re going to be eating up a lot of space in order to soundproof properly.  One of those annoying facts of life. 

Here’s our wall-building goal.  The drywall on the interior of the RWAW should be as disconnected as possible from the drywall on the outside of the RWAW.  By de-coupling the inner layer and the outer layer, we reduce sound transmission between the two.

Now, there are three basic ways to build these walls.

1.        A Double Wall.  This is just two independent 2x4 stud walls erected next to each other, with drywall on the outside of wall 1 and the inside of wall 2.  Simple, with an amazing STC of around 60.  That’s nearly 12 points higher than an 8” thick concrete wall!!!  The downside is that you end up using a lot of wood, and the wall is very thick, eating up a good deal of space.

2.        A Staggered Stud Wall.  This is an ingenious way of constructing a single wall with the benefits of a double wall.  Instead of a normal 2x4 wall base, use a 2x6.  Then, erect your 2x4 studs flush to one side of the 2x6…then do it again, on the other side, with a whole separate set of studs!  When you’re done, you’ve got a staggered pattern of studs, but the extra width of the plate keeps the studs from either side extending to the other.  STC is in the mid 50’s.  To see an illustration of what I’m talking about, check out http://www.lis.net.au/~johnsay/Acoustics/Pages/STC%20Chart.htm

3.        A Single Stud Wall with Resilient Channelling.  Resilient Channels are long metal strips that you install horizontally across the studs or an initial layer of drywall.  Then, you nail the drywall onto the metal strips, so they literally “hang” off the metal, never actually connecting directly to the studs, thus never transmitting directly to the other side.  See the above link for an illustration.  This method is worth about an STC of 50.

Each of these methods works.  Remember, when you’re building these walls, you’re not going to be able to squeeze into your 6” gap to erect drywall!  So…you’ve got to install the drywall on the outer part of the new wall BEFORE you erect it!  Tricky…and heavy to lift.  Two MUST DO’s when building these walls.  You MUST run fiberglass insulation in these walls.  It’s fairly cheap, and you won’t get these STC ratings without it.  Don’t pack it in too firmly.  The denser it is, the less of an air “trap” it is.  You don’t need anything fancy either.  R-13 should do fine.

Secondly, you MUST double up on the drywall on at least one side of the wall.  This gives us our crucial added MASS, to help cut down on those bass waves.  I found that an inch of drywall on each side did a great job.  You might need less.  You almost certainly won’t need more.  Remember, drywall is heavy.  More drywall than normal is more heavy than normal.  Be careful when building any structure to ensure that you’re not exceeding approved standard safety guidelines.  Again, I am not a professional.  Be sure to get some professional advice if you have ANY questions.  Hell, reread the warning at the beginning one more time.  Just in case it didn’t sink in.

On to windows.  If you can block ‘em out, do it.  They leak sound.   Stuff the sill with fiberglass, then board it up.  You can use soundboard, also called fiberboard or particle board or homosote, depending on where you buy it.   It doesn’t actually do anything better than plywood, but it’s cheaper and lighter.  If you’re going to build a window between your control room and your RWAW, make sure that you use two thick panes of double-glazed glass or 1/2” plexi.  Angle the panes like an “A” to avoid creating more standing waves problems.

Now, the door.  You COULD go out and buy some horrendously expensive commercially soundproofed door, but I think that’s overkill.  Yet, most home doors have an STC of about 20, which is pretty insufficient.  Even if you install a sold wooden door with a really good seal on it, you’re looking at around 28.  However, a hollow steel door with a good seal gets you to 30.  So…what I recommend is installing a double door…two hollow steel doors with a good seal (make sure to get the right kinds, i.e. right hand/left hand, inswing outswing, so that you can get in your room!).  Stanley makes a plain model D-1 with a refrigerator style magnet seal that works great.  Combined, the two doors will get you up around 50.  And since your wall is liable to be thicker than the average wall, it shouldn’t be too much of a pain to make the entrance a double door.

Floors and ceilings are big huge pains in the butt.  Both should be viewed using the same principles we applied to the wall construction.   For the floor, you can use your pre-existing floor as a subfloor, then elevate a new floor, with special thick rubber pucks as separators.  You can find products like those, and lots of other great stuff, at www.soundproofing.org   For ceilings, you can build a false ceiling using your new walls as support, then insulate the gap between the false ceiling and the original ceiling, or you can “hang” a new ceiling from the original wall with resilient channelling.

Finally…the last step.  CAULK.  Caulk everywhere you see a gap.  It’s those little gaps that hurt you.

Which leads us to our final rule of soundproofing.  A room is only as soundproof as its weakest part.  Pay careful attention to the door seals, electrical outlet wallplates, audio wallplates, etc.

Anything Else I Need To Consider?

Yeah.   Like, now that you’ve sealed yourself in an airtight container, how are you gonna breath?  Ventilation/AC is a MUST.  The duct will obviously be a breech in your seal, so caulk around it, then consider using some specialized spray foams that coat the inside of the duct and help trap sound waves.

Oh, and some light would be nice.  The new fluorescents don’t hum so much and shouldn’t screw with your recording, and they don’t add heat.  Otherwise, go for regular bulbs.

Why Does My Room Sound So Terrible?

Because it’s a hard-walled room from which little-to-no sound escapes.  What you need to do is treat the walls (and perhaps floors) with acoustic foam, bass traps, possibly diffusers, etc.  This FAQ deals with stopping the transmission of sound, rather than dealing with the reflection of sound.  Check out rec.audio.pro for tips.

Does This Really Work?

Yes.  I built a room-within-a-room on the first floor of a guest house, converting the garage area.  Since no one lives on the second floor, I didn’t have to deal with the floor or the ceiling, just the walls.  I sealed the garage door off, and caulked it shut.  I used a double wall construction with 1” of drywall on each side, and a double door system as described above.  I can tell you that I play my drums as loudly as I can at 3 am, and no one’s the wiser.  The dB meter registers no change AT ALL.  If you listen carefully, you can hear the faintest sound…mostly the bass.  Walk about twenty feet away, and it’s gone.

How Much Does This All Cost?

Hard to say.  Are you doing it yourself?  If so…I’m in awe!  This is quite a bit of work, and tricky, even for experienced builders.  I used a licensed, bonded and insured contractor, who constructed a RWAW that was about 13’x17 for about $5000 all in.

Soundproofing FAQ - Craig Mazin ©2000




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