When micing a guitar cab, it’s important to remember how critical of a stage this can be in capturing the best representation of your tone. With a basic understating of guitar cabs, microphones and a little bit of physics, it’s shouldn’t be very difficult to get decent sounding tones. On the other hand, even if you think you know everything, it’s not that hard to make a couple bad decisions that can totally ruin the tone of an awesome guitar rig.
Before you even pick up a mic, it’s important to know how its position in relation to the speaker will change your tone. If you have never looked inside a guitar cab, it wouldn’t be a bad idea to check it out. Either remove the grill or shine a flashlight through it to see the speakers inside. Depending on the size of the cab, you’ll have one, two or four speakers. The small dome in the middle is called the dust cap. Placing the mic “dead center” over the cap will give you the brightest sound, meaning it will have more higher frequencies. Sometimes, a SM57 on the dust cap will be all you need, but if the sound is too shrill or fizzy, you can move it to the outer edge of the speaker. Placing the mic over the edge of the speaker will give you a warmer sound. The part in between the dust cap and the edge of the speaker is called the cone. By varying the position of the mic between the cap and the edge, you can give get a wide range of tones. Even a difference of an inch can dramatically change what gets recorded.
Now that we’ve talked about mic positioning in 2D, let’s add the third dimension. One thing to consider before you start recording is how much “room” do you want to hear. That is, how much natural reverb from the space you are in do you want to add. This varies greatly from genre to genre and even between artists within a genre. The way to add “room” to your sound is by backing the mic off the cab. The more distance there is between the speaker and the mic, the more likely the reflected sounds (reverb) will be picked up.
The type of microphone you choose has a major impact on what will actually be recorded. For example, the industry workhorse Shure SM57 has an upper midrange boost of about 6dB, which gives guitar cabs a biting edge that helps them cut through the mix. However, if the same cab were miced in the same position by an RE-20, the resulting recording would sound completely different. The RE-20 is well known for being able to handle low end sounds, such as kick drums and bass cabs. Think of different mics like different brushes for a painter. Not all of them are suitable to be used on everything. Some are. Some have a very specific function and rarely get used. A good way to learn about mics is to browse online music stores and forums to see how other people are using them. Though, don’t let what you read make you think a certain mic can only be used on one particular instrument. You will learn more through experimentation than anything else and sometimes misusing a mic can lead to some great tones.