As the largest point of connection to your neighbors, your walls are a major source of neighbor noise.
Fortunately, they're also one of the easiest things to fix when it comes to sound transmission. Let's start by taking a look at how walls are constructed, so we can see why noise is getting through and how we can stop it.
When contractors are building apartments or townhomes to sell, they're generally trying to keep construction costs as low as possible. To do this, they'll often construct walls in the cheapest way possible, with shared walls containing nothing more than some 2x4 studs with a layer of drywall on either side. In some buildings, they may add a layer of fiberglass batt insulation to help with noise and temperature control.
Luckily, there are many ways to improve the STC ratings on your walls and help block more sound. The quickest and cheapest solution is to add a single layer of regular 5/8" drywall over your existing walls. Simply screw it in place so that it attaches to the wood studs. This second sheet of drywall will increase the STC rating of your wall by about 10 points [source: Guardian].
For more extreme noise situations, try QuietRock. This drywall product uses special technology that keeps sound waves from penetrating your walls. It has the same fire-resistant capabilities as regular drywall, but by adding just a single layer to your existing walls, you can take your STC ratings up to an average of 58. Add two layers, and your walls will be around STC 80. At that level, your neighbors could start a rock band in their home and you'd barely notice [source: Quiet Solution].
Finally, if you'd like to reduce sound without adding drywall, consider hanging panels wrapped in fabric. One of the most popular products for blocking sound in apartments is called Homasote. It's a lightweight composite product made of recycled newspapers and cellulose fibers. By wrapping Homasote panels in a nice fabric, you can reduce the noise coming through your walls by about 20 percent, while adding to your home's décor [source: Homasote].
Of course, your walls aren't the only paths that noise can take to your home. Read on to the next section to learn how to block noise from upstairs neighbors, as well as how to soundproof your doors and windows.