Right from the get-go, we need to distinguish between soundproofing a room for recording a podcast, and improving the acoustics of the room. In this article, I will discuss only sound-proofing a room, but if you want to improve the acoustics of your room, check out this article.
Soundproofing is the practice of reducing the penetration of noise from outside the room into the room where you will record your podcast. Improving the acoustics of the room is changing the way your voice sounds in the room (echo, ring, etc).
Background Information for Beginners
Before you begin any soundproofing projects, I highly recommend simply buying a high quality directional microphone. If you use the microphone that I recommend for podcasting, you likely will not need to do anything to your room to make the sound quality improve.
Most microphones–especially inexpensive ones–have a wide pickup pattern. That means the mic will capture sound coming from any direction. This works well for recording a group or recording an area where sound is coming from, but it is a disaster for podcasters. It means the sound coming from the computer fan in front of you is just as likely to be recorded as the sound of your voice.
Podcasting requires a directional microphone, which only picks up sound from one specific spot and is held right up against your mouth so that no other sounds are captured.
Even when my home office was in a small bedroom in my home and the kids ran around right outside the door, none of the outside sound affected the audio because the mic was only pointed toward me. Get a very directional microphone and soundproofing may not even be necessary.
Next, keep in mind that soundproofing is not a simple project, and it is not cheap either. While acoustics can be improved for very little money, soundproofing often requires making changes to the actual structure of the room. Before beginning you should know that the easiest answer may be to simply buy a good microphone and find a quiet room in your house to podcast from. Having said that, the following are the two steps that I took to sound-proof my home office for podcasting.
Step One: Plug Holes
To understand proper soundproofing, consider the following experiment. Walk outside your house near a window and have someone stand inside the house by the window. When you talk, the sound will be quite muffled and barely audible through the wall. Now open the window just a tiny crack and continue talking. Just the tiny crack makes it seem as if there is no wall at all, and the person is standing right next to you with no obstacle in-between.
The point of the exercise is to help you realize that no amount of sound board, acoustical foam, or anything else will matter if there is any unobstructed crack between the podcasting area and the outside sound.
The most common problem with sound-proofing a room for podcasting is the crack under the door. All interior doors have a small gap between the bottom of the door and the floor. Until this is addressed, little else will matter.
There are a few options for how to address this: (1) Purchase a commercial sound-deadening door jam specially made for sound studios (hint: incredibly expensive), (2) put something under the door like a thick chunk of a foam camping mat, ensuring it fits flush.
In my personal home office, I had the builder install two solid core doors with thresholds going into my office. The threshold fills the gap below the door, and the solid core door (like the front door on your house, not like other interior doors) helps deaden sound.
Step Two: Thicken barriers
Sound can best be stopped by increasing the density of what it needs to travel through. Adding acoustic foam to your walls is perfect for improving the acoustics of a room, but will do basically nothing for sound-proofing a room–especially if only parts of the walls are covered with the foam.
Higher pitched sounds are stopped easily by traveling through pockets like in foam, but lower pitched sounds should be addressed by having a dense wall to stop it.
In my personal office, I had the builder install insulation in all of the walls around my office and the bathroom and bedroom next to my office. That’s for the high-pitched sounds. Then, I had the install sound board to prevent the low-pitched sounds from penetrating the walls.
A note on sound board, while my office ended up with excellent soundproofing, if I could have done it again I would have asked the builder to use sound-proof drywall instead. Sound-proof drywall is better at deadening the sound because it is installed without cracks (taped and mudded at all cracks) whereas soundboard has tiny cracks between sheets, which creates the problem like the window in step one.
Sound board is quite inexpensive and readily available, however. It usually only costs about $25 per sheet at any hardware store. Soundproof drywall usually has to be special ordered.