Mic'ing Guitar
So here’s another topic that has been written about abundantly. Still, this brief outline might help you to quickly get a good sound when micing a guitar amp so let’s dive in.
The unofficial de facto standard for micing a guitar amp is typically this formula: 1 Shure SM57 placed about 1” or almost touching the speaker grill pointing somewhere between the speaker cone “cap” and the cone itself and then slightly angled. The amazing thing about this simple technique though is how much the tone can be altered simply by moving where the mic is pointing at the speaker or changing the angle. For this approach to work the guitarist should get their tone in the room first and then the mic can be placed. Two people are needed – one in the control room or under headphones and the other moving the mic slightly until the optimal sound is obtained. After all, the goal is to get it sounding right coming back through the mic and studio monitors and that may be different than what’s heard in the room. To change it up a bit, try using an Audix i5 mic instead of the 57.
Next up, try adding an ambient mic in the room to capture some “air”. A large-diaphragm condenser can work great in this role. Set it 3 feet or more away from the amp pointing directly towards it. The further back you go, the more the room enters the sound equation. Make sure to listen to both mics coming through the board in mono to make sure there are no strange phase issues. If there are, simply moving the room mic forward or back should remedy it. You can also place the 2nd mic off to the side of the amp but closer in for a nice blend of room and “body”. Again, having someone move the mic while you monitor the sound in headphones or the monitors is immensely helpful.
You can go with a third mic for even more options. Often a ribbon mic can be placed close-in on the speaker to blend with the primary mic. Ribbons have a mellower top-end in general and can smooth out a harsh sounding amp. If you can track all the mics to individual channels it gives some great options at mixdown. When placing another mic close to the primary mic, you must consider phase unless they are an identical distance away. There is a 3-1 rule in general mic placement. That is, the second mic should be placed at least 3x the distance from the sound source as the first mic. For example, if an SM57 is sitting about 1” from the amp speaker grill then the next closest mic should be at least 3” away. You can, however, also place the 2nd mic right alongside the first at the same distance and angle and check for phase.
Speaking of phase… What you’re looking for is a nice full sound from the multiple mics. Phase issues will show up in the form of causing a thin or “washy” sound. It can also show up when you sum the mics to mono in the form of a comb-filtering effect where certain frequencies are cancelling each other out. Make sure you try to address phase during the micing process rather than after the recording is done – it’s more difficult to remedy after the fact.
There is so much written about micing guitar that this isn’t breaking any real new ground here but willingness to experiment by adding 1 or 2 more mics into the equation can give some great results. The reason the close-mic approach of the SM57 is referred to so often is because it’s proven to work. Remember though that you can’t expect to get great sounding guitars if they don’t sound good at the source to begin with. Mic techniques don’t make up for a poor sound.