Soundproofing is also known as ‘Isolation’ for the simple reason that it stops sound from disturbing people inside the house or around you. Soundproofing is also important because it stops all the noise from coming into the room and ruining your jam. In the mixing room (also known as control room) it is essential to keep the noise-floor to a minimal level so it’s not just concealing the details but also restricting dynamic range of the room.
Let’s just say you have a home theater system that is capable of 100 dB optimum output. In a normal room without soundproofing, the noise floor will be usually around 50 dB. Things like HVAC fans, people around your house, sound coming in the room through the windows etc. all contributes to this. In that case, the maximum dynamic range your system can achieve is approximately 50 dB. But if we build a room where we do focus on soundproofing, we can get down the noise-floor down to 20-30 dB. If the noise-floor does come down to 30 dB and we have the same equipment, we can easily achieve a dynamic range of 70 dB. This concludes in more dynamic range, it takes less to maximize as the equipment is loud enough to hear smallest of the details.
Sound travels through 2 ways, i.e.: through air and through structure.
Sound that travels through air is comparatively easy to understand. With any accessible holes in the room and the sound leaks. Outlet, switches, canister lights, gaps underneath the door, HVAC ducting, etc. are all very clever and admirable sound transmission paths. However, sound travelling from your structure is much less understood. Sound vibrates through walls, ceiling, floor or even tin ducting! When they are caused to vibrate by the sound in your room, the other side or what they are connected to also creates vibration and recreates that sound in other parts of the rest of the structure. If you think that concrete basement floor isn’t a flanking path for sound to get to the rest of the structure, you are wrong! Flanking is a term that is used to explain a path where the sound ‘goes around’ the barrier of the space.
So in this case, how does one deal with problems of soundproofing? It all comes down to your budget, situation and whether the room is already built or not. Let’s take an example to make the issues of soundproofing more subtle and easy to understand.
Your existing room is to be used for a listening room or to put up with the home theater in the room. Bedrooms are not precisely next to this room but are close enough that transmission of the sound can become an issue.
Let’s see how we can tackle this and make it sound proof.
- Seclude the wall (Insulation) – This is not an expensive procedure at all and can get you great performance gain as well. The walls have now turned into sound-absorbers in the bass and also do not transmit mid/high frequencies in either direction of the room. The walls also do not sound like a big drum.
- Replace the Door – It is extremely easy to do that! Replace the door with a sturdy wood door and add seals to the door. One of the greatest sound leak in any room is your door. Hollow interior door are ghastly blocker of bass energies.
- Baseboards – remove the baseboard and use a 50 year Latex caulk or acoustic caulk to caulk the gaps under the drywall (between the drywall and floor) and also caulk the wall to the floor to prevent air penetration.
All that you have done in Level 1 of sound proofing, you can add some more to get better performance gain.
- Discard the prevailing outlets and switches to build an MDP “backer box” behind each of them. Make a hole in the top of the box big enough for the Romex to enter and block that. Change with old work boxes and if you can’t take down the drywall to build boxes, make use of putty pads on the rear and sides of the plastic box to add some mass and seal it up tightly. Redo this for any canister lights in the room. Use IC rated cans if you are going to box around them.
- If it is accessible, replace any tin duct-work with flex tubing and soundproof it in an MDF box with 90 degrees bends in it. This does not only just makes the room quieter but also refrains the sound from going out. Generally, HVAC is ignored while soundproofing, but it is extremely important!
While level 1 & 2 can give you great performance gain, level 3 makes soundproofing extremely easy!
- With all that you have done in the room with level 1 &2, add another layer to the wall and use Green Glue between the layers. This provides tremendous gains in soundproofing across the spectrum down into the deep base range, the additional mass of the dry wall stops a good amount of sound by itself. Green Glue also provides ‘visco-elastic damping layer’ between the sheets.
- Build a plug for any windows in the room. Make the front something that has mass like MDF, fill the rear end with insulation. If the windows are recessed in the wall, make the plug small enough to fit in while using ¾” foam weather stripping for a seal. If you can’t do that, make a 2×2 frame around the window that allows you to trim and slide the plug around the outside.
- Now you need to focus on the floor – You can either suspend a floor using Dri-Cor or you can use a precisely made rubber dampening layer and add new layer of subfloor. You can also add a third layer of Gypcrete between the prevailing floor and the rubber matting. The floor joist beneath you is probably shared with the remaining structure, you must remember that. Bass frequencies will move through to the structure and building despite of concrete flooring.
- You can add another HVAC system for the room, Mini-Splits are also cost effective in that case.
Even with so many efforts, there will still be some moment. But with all the soundproofing, it all acts like one big woofer!