If your exterior wall has a door or window, then this is the best place to start. Doors and windows are typically in the STC 20-30 range, much too low when compared to the average exterior wall. Assuming the door or window is small in comparison to the size of the wall, it can rate within 10 STC points of the wall without significantly affecting the overall STC rating of the wall.
If your wall has both a window and a door, then the window should be treated first since it is likely the weakest of the two. Replacing your windows with ’soundproof’ windows will help performance. To replace an exterior window, first remove the perimeter of the window frame. If the exterior is rock, brick, or stucco, then replacing the window could turn into a significant project. Replacing your windows with a high STC rated window will provide the cleanest look, as well as pretty good results from a single window.
However, this construction headache can be avoided by adding a second window to the inside of your window frame. The STC rating of the opening improves to at least the mid 40’s STC with the addition of the second double pane laminated window. A dramatic improvement achieved with minimal construction.
At that point, your windows will perform better than the average exterior wall. There are several companies that sell windows that can be used for retrofitting on the interior side of your windows frame. Run a search to find a company that sells retrofit windows.
Watch the video below to see the effect of adding a second window to your window installation.