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There are times when the most powerful soundproofing techniques are needed. In this article I will go over the techniques that yield the most isolation for your soundproof design. These techniques may be needed if you have an especially loud source, like drums, you need to isolate or if you live near an especially loud neighbor, like an airport, and need to keep those sounds out of your studio.
1) Let's Review The Basics
To understand the best isolation techniques we need to revisit the fundamentals of sound isolation. To soundproof a room we need three things:
a) Mass
b) An airtight room
c) decoupling from our outside structure
Mass involves adding lots of weight to our floor, walls and ceiling. It really is as simple as that. The more weight your assemblies have, the better your sound isolation will be. The single most useful tool for increasing isolation is to add mass.
Next, we have air. For a room to be soundproof it must be airtight. This means every possible hole must be filled with acoustic caulk, acoustic putty pads, or special acoustical seals around doors. Even a small hole will let in sound, so we must ensure the room is sealed completely.
Lastly, it is important to fully decouple the outside structure from the inside structure. This is the common term "a room within a room." For extreme soundproofing we are going to use the best decoupling techniques to ensure sound does not travel through our structure into our soundproof room.
2) Extreme Soundproof Floor
The best soundproof floor is easy. It is a concrete slab poured over earth. Yup, no second stories here. For the best most extreme soundproofing you need to stay close to the ground. A concrete slab poured over earth will off you the best sound isolation period. Done deal!
3) Extreme Soundproof Walls
If you need to keep out the sound of a kick drum, an electric bass amp, or the rehearsal of a heavy metal band you are going to need some powerful walls. Now you may have heard a term STC. It is helpful, but misleading. The reason? STC only measures frequencies down to 125hz. The most complained about noises are always bass or low frequencies below 125hz. I know, this is a total bummer. It means we have no way of knowing for sure if our soundproofing will fully work in the low frequency range. Yup, it sucks and I wish the labs would measure lower, but I believe the reason is they cannot guarantee accurate results sub 100hz. Don't quote me on that, but I did read it on the internet and it would explain this issue with STC ratings.
So, the best you can do is build the most soundproof wall within your budget and available space. Here are some ideas for a super soundproof wall.
A) Two Concrete Walls with Compacted Sand
Now, this is extreme but you could build two concrete block walls filled with dry compacted sand and achieve very high isolation. It is important to put fiberglass insulation between your two walls to achieve maximum isolation. The minimum distance recommended between the walls is 1", but you guessed it, the greater the air gap the greater the isolation. So, if you had the budget and space you could put a 1 foot air gap and really attenuate those low frequencies.
B) A Double Walls System With 4 Layers of Drywall and Green Glue
Now, this is hardcore! We know that a double of mass will increase isolation by about 5dB. It may not seem like much, but it does help, since we hear a halving of sound at 10dB. That's like turning the volume knob on your room. Here is the plan. Notice on the chart below that the best STC rating is the two walls with an air gap and two layers of drywall on each side with fiberglass insulation in the middle. To get even better isolation we can add two more layers of 5/8" drywall to each side. Now to go crazy, we can get even more attenuation by adding Green Glue in between the two layers of drywall on each side. Just like our concrete wall we can increase the air gap and achieve even more isolation. I am very confident that this would really deaden the sound of drums, loud band rehearsals and most of the low frequencies.
*A Word Of Warning - Soundproofing is not perfect. You could spend $150,000 building a concrete bunker and maybe still here 40hz. The goal is to turn down the volume of sound in your studio to an acceptable level for your neighbors and you.
4) Extreme Soundproof Ceiling
Now that our floor and walls are super soundproofed we need to tackle the ceiling. The best way to soundproof the ceiling will be to frame it off the inner walls. So, with our concrete blocks you can build a frame off the inner block walls and with the wood walls you need to frame of the inner wood wall.