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Hello, and welcome to part four of our Soundproofing Series, “Advanced Structural Solutions You Can Try”! This is where you will learn tried and proven strategies for effectively eliminating noise in any studio space. 

Before we get into it, make sure to check out our previous installment, Soundproofing Series #3: What You Need To Know About Barriers, Absorbers, And Sealants. That particular article contains information about soundproofing solutions that you can use for the procedures outlined below. 

Let’s get started! 

What really causes sound transference? 

Sound transference is precisely what you’re trying to avoid when soundproofing. But what causes it exactly? More importantly, what can you do about it? 

Two of the biggest causes of sound transference between rooms are vibration and air gaps. Let’s go over some possible solutions to reduce them.

Vibrations and its effect on noise levels 

Remember, vibration=sound. If something outside your room is causing something in your room to vibrate (wall, floor, door, windows, etc.), you are hearing sounds that you don’t need to be hearing. Fortunately, you can address some of these issues through the process of decoupling. Here are some steps on how to do that: 

  1. If you have a washer, dryer, refrigerator, freezer, or air compressor running in a room next to you or above you, they will cause your walls or floor to vibrate. If you are on the same floor or in a room beneath it, the vibrations will travel through the floor into your space, creating audible sound waves. A quick and no-cost solution is to only run those appliances when you’re not working in your studio. 
  1. Anti-vibration pads are useful if your room shares a wall with another room that has a swamp cooler in it. Although you might not eliminate the swamp cooler’s sound, you can reduce most of the vibrations it produces.  

Anti-vibration pads are small squares made of rubber and/or cork. They are pretty cheap and available at many HVAC supply outlets. A quick web search will also pull up several online merchants that sell them. I suggest looking around for the best deals, though, because they seemed a bit more expensive online at first glance. Use the appropriate type and as many as you need to provide the degree of sound isolation you require.

  1. If your air conditioner’s compressor is installed on your roof, you might want to use anti-vibration pads there too. Most should already be on isolation pads. If they aren’t, you could probably ask the building manager/supervisor to install them for you.
  2. If you have direct access to the air ducts that heat and cool your room, you can cut into the metal supply and return duct and insert a short section of flex duct or rubber joint. This will decouple the vibrations that the AC or furnace sends along the ducts.

    The flex duct will have to be the right length because it will affect the amount of air passing through the vent. If it’s too long, your HVAC system may not work properly. If it’s too short, it probably won’t have a noticeable effect on the airflow. It might be best to consult an HVAC specialist if you want to explore this option.  

Keep in mind that these solutions work best if the noise is coming from a room and NOT the walls. If the noise is coming from the walls, you might have to resort to mass-loading, which we will discuss later in this article. 

Closing up air gaps to prevent sound transference 

As with vibrations, dealing with air gaps involves eliminating as many of them as possible. 

Imagine for a second that your room is suddenly filled with water (forget about water damage for now). Any opening that allows water to leak out of your room will also allow sound into and out of your room, which means your microphones can pick them up.

If closing your doors and windows isn’t enough to block external sounds, you need to plug or seal those gaps. Here’s how you can do that: 

  1. Remove the covers from all your light switches and electrical outlets. To be safe, turn off the power first and don’t touch any wires anyway!

    Once the covers are off, you’ll see gaps where the drywall had to be cut to fit around the electrical boxes. Fill these gaps with caulk. If budget allows, use an acoustic caulk. If not, at least use a silicone caulk that is resistant to shrinking or cracking.
  2. Gaps at the bottom of doors allow plenty of noise through. It’s basically the same as leaving your window open an inch or so. A quick search for “draft blockers”, “door sweeps”, or “automatic threshold door bottom seals” will pull up several effective solutions, but anything that blocks the gap will suffice. You can try towels, rice bags, etc. 
  1. Seal the gaps around the edges of your door. The adhesive-backed raindrop-shaped silicone smoke-seal gaskets usually work best for these applications. When the door is closed, it flattens the “bulb” and seals the door. You could even use two seals, so when the door is closed, both the face of the door and the edge are sealed. 
  1. Your door is likely a standard hollow-core interior door. If you have tried the tips above and still hear a lot of noise coming through, consider upgrading to a solid core door. Most door suppliers will help you get a door that fits your existing frame.

    Solid core doors will make a big difference, provided you use door jamb smoke seals and seal the gap at the bottom. Otherwise, the upgrade will be a waste of time and money. Think about it this way: if a boat has five holes with water coming in, plugging four of the five holes won’t solve your problem. You need to plug ALL the holes, or you might as well not plug any. Make sense?
  1. Remove the covers of your light fixtures. Like the light switches and electrical outlets, you will need to seal the gaps between the electrical box and drywall.
  2. Seal the bottom of your wall. If you’ve tried everything and noise still comes through the wall into the room, you may need to seal the bottom of your wall. The easiest way would be to caulk the gap between the bottom of the baseboards and the floor. But this results in an unsightly seal and will cause additional problems if you ever have to remove your baseboards in the future.

    A much better option would be to remove your baseboards and apply caulk where the bottom of the drywall touches the bottom 2 x 4 or “bottom plate” along the floor. You may also want to use caulk where the plate touches the floor. You don’t have to worry about the top gap where the walls meet the ceiling, as this has already been sealed during the mud/tape phase of drywall installation.
  3. Seal the gap behind the trim between the frame the door is hinged to and the wall opening. Unfortunately, foam-type filler sprays probably won’t do the trick. What you need is dense mass, such as thick paste that won’t crack or shrink.

    Many commercial studios have metal door frames filled with sand or concrete. It’s very unlikely that your door is built the same way. To fill the gap around my door, I use a combination of wood strips where appropriate and closed-cell backer rods where I can’t use wood fillers. I then seal everything with dense but flexible non-sag, polyurethane expansion joint sealant.
  4. Seal or plug the vent. Now for the tricky part. If your room has a central air heating/cooling vent, you probably have a direct connection to every other room that shares the system. You might remember yelling through these vents as a child. If so, you know how well they allow sounds to pass through.

    One solution is to create a temporary plug to seal the gap. You could use a piece of fiberglass wrapped in cloth, for example, or a bag filled with old T-shirts.

    Another option is to seal off your central air duct and have a dedicated heating/cooling solution for your room that isn’t connected to any other room in the house. Mini-splits are popular and very effective, but rather expensive, costing several hundred to several thousand dollars.
  5. Consider plugging your window with a fabric-wrapped piece of fiberglass. This can work wonders for reducing the noise coming in through your windows. A quick web search for “window plug” will call up many DIY and manufactured options. Who knows? Something that grabs your attention could be the perfect solution for you. 

All about the mass: Solving your noise problems for good 

If you’ve tried all the tips above and are still struggling with noise, the next step is to add mass to your walls, floor, or ceiling. 

Mass is the enemy of vibration. The heavier something is, the harder it is to get it to move. I have to emphasize though that EVERYTHING‒even the concrete and steel Tacoma narrows bridge‒will vibrate. 

We aren’t going for zero movement. Instead, we are trying to make it as difficult as possible for the vibrations to find their way into your room. 

The more mass an object has, the less susceptible it is to vibration and the lower the resonant frequency becomes. Consequently, you are less likely to hear the problem frequency as you mix.

The drywall used in most homes is typically ½” ultra-light material, which just isn’t dense enough to do more than conceal you from view and possibly lower the sound of someone sneezing. 

Furthermore, most walls don’t even have any insulation. This means that if someone is playing music or watching TV in the next room, nothing will keep the drywall from vibrating along with the acoustical energy being produced. 

The resulting sound waves will easily travel the 3.5 inches through the wall, over to the drywall on your side. It will then start to vibrate sympathetically and the sound produced will likely make its way into your recording. Your walls then essentially become large speaker cones for the sound from in the other room. The noise may be reduced a little, but not by much. 

If the noise problems are coming from inside your walls, you will need to add mass to them. The easiest way to do that is by adding ⅝” drywall layers to the outside of the existing wall. 

You could also install a product called “mass loaded vinyl”, which is sandwiched in between the outer wall and a new sheet (or two) of ⅝” drywall. This solution isn’t cheap, but the added mass will significantly reduce the sounds coming from inside the wall and those transmitted from the other side.  

Why soundproofing requires an “all or nothing” approach  

In many ways, isolating your room acoustically is a slippery slope. For optimum results, you need to reduce vibration and seal all air gaps. In many ways, it really is an “all-or-nothing” undertaking. 

Remember our example about plugging holes in a boat? Unfortunately, physics doesn’t award results for effort, clever hypotheses, good intentions, or money spent. But you need to start somewhere. If you’re in a leaking boat, plugging some of the holes is way better than not plugging any of them! 

I suggest starting with the easiest and least expensive solutions and work your way from there. Don’t worry! As tedious and challenging as it all might seem, you will become more and more inspired as your room becomes quieter by the day. When you get to a point where auditory masking and inverse square law take over, your work will be done!

That’s all we have space for right now. Be sure to check out the conclusion of this series: Soundproofing Series #5: Additional Resources On The Art And Science Of Soundproofing

– Alexander E. Jenkins

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