Being in the acoustic treatment space, we get questions about soundproofing and sound sound dampening quite frequently. Here is a quick guide pointing out some of the primary factors you’ll want to take into account when building a soundproof room, or adding soundproof characteristics to an existing space.
Soundproofing is a common need for many situations. It can range from simple endeavors, like heavier curtains and thicker doors, to fully isolated anechoic chambers where no sound can enter or leave.
There are a number of things to consider to soundproof your space. The first thing is to be clear about what area you soundproofing, and which area you soundproofing it from. Are you soundproofing a room so the kids can play and the parents watch TV? Are you soundproofing a room so the band can play at full volume and the neighbors aren’t going to call the police? Just think about what you’re trying to do, and then visualize all the surfaces that are going to play a part in the process. Any wall, door, window, ceiling, or floor that separates those spaces will likely need to be addressed. There may be vents, ducts, or other openings that can let sound escape as well.
The main ways to reduce sound transfer are going to be to close up any air gaps, decouple surfaces, add mass to barriers, and introduce sound absorption panels or materials. Each method has its own applications, and most soundproofing jobs use a combination of these methods.
The first thing to do is to close up any air gaps between the two spaces. If there are uninsulated areas around windows, caulk and stuff with insulation. If there’s a crack under the door, add a seal or wiper to reduce air transfer. Add weatherstripping to the door if there are cracks around it where it doesn’t seat in the frame. Air vents can sometimes carry sound to other rooms, especially if they’re a large metal duct. Test to see if this is the case, and if so, see if there’s a way to replace that section with flexible, insulated ducting. Light switches and receptacles are other items that aren’t generally air tight. There are a number of products to seal the front side of the receptacle under the cover, and ways to reduce both airflow and sound from the back of the box.
The next thing is to decouple surfaces wherever possible. Decoupling simply means add separation between surfaces exposed to sound and the surfaces where you want no sound. If you were building a space from scratch to be completely soundproof, you would build a separate wall for the area you want soundproofed, then add insulation between the inner and outerwall. A less extreme example is building a single soundproof interior wall. Instead of having a single stud be the mounting surface for drywall on both sides, the wall would use half depth studs, off center, on each side. So you’re in theory making two thin walls, that don’t fully touch, and adding insulation between them, to replace one standard wall. That way sound vibrations to the exposed surface don’t make it to the other side of the wall.
If you are working in an already existing structure, and don’t have the luxury of building walls from scratch, you can still use the decoupling method to lessen those sound transmissions. You can add a layer of drywall to your existing space with a layer of Green Glue Noiseproofing Compound behind it. The Green Glue compound doesn’t fully harden, and remains somewhat viscous throughout its life, meaning it can absorb some of that sound energy and acts as a mechanical separator of those two surfaces.
Adding a layer of drywall also adds mass to the wall. Adding mass to objects lowers their resonant frequency, meaning they will vibrate at lower frequencies are less susceptible to high frequency transfer. This also means it takes more energy to vibrate the wall. If you have a thin, hollow core door, you’ll find that it doesn’t do a very good job of stopping sound. The best way to address that issue would be with a thicker, heavier door. It will take more energy for sound to pass through. If there’s a question on finish materials or decor, thicker and heavier will generally suit your needs better than thinner and lighter. Heavier drapes or curtains, for example, can make a considerable difference in the transfer of high frequency noises through a window.
If you have windows in your space, and they’re a source of concern, you may want to look into some window plugs. These can be constructed rather easily and can make a huge impact on noise transfer both in and out of a room. They generally have a frame that fits into the window frame, and either a gasket that slides between these two frames. Or there is a front panel with a gasket that slides back and squeezes directly to the wall. Then there are is generally some sound absorbing insulation in the frame, and then two decoupled panels on the front.
There are weighted vinyls and other heavy insulation that you can add to walls and surfaces as well, but less common in these situations.
Sound absorption is the last method we’re going to talk about with regards to sound proofing. Sound absorption materials or generally open cell or fibrous materials that absorb sound energy, by turning it into heat. These can be configured into panels and placed on primary walls to help absorb the sound before it reached the wall. You can make these panels using mineral wool insulation. The thicker/deeper the insulation, the deeper the frequencies it will trap. This also goes for other plush materials in the room. Rugs help trap higher frequencies. Thick couches and mattresses also absorb some sound and keep it from bouncing off of the walls. Every bit of sound that you can trap is that much more you don’t have to worry about managing elsewhere.