A few more things to think about
OK, before we get into what mic to use for what purpose, and where to place it, here are a few more things you hafta be aware of. One is called "musical intrument radiation patterns" and the other is "near-field placement vs. far-field placement".
The most common question here is "how do I mic an acoustic guitar?", followed by vocal mic techniques. Let's look at the first question because it's more complex than it appears and it's actually made up of two parts.
Musical intrument radiation patterns
Guitars, violins, stringed instruments, in fact, all instruments radiate notes differently at different frequencies!! Read that again: Guitars, violins, stringed instruments, in fact, all instruments radiate notes differently at different frequencies!!
What does that mean exactly? It means that different parts of the instrument's body are used to produce different notes! Just pointing a mic at a guitar is no guarantee that you'll get what you want. Unless you understand how guitars generate sound, the best you can hope for is to somehow get lucky. Here are two links that show how the guitar top changes with each note:
Chladni guitar top radiation patterns
Radiation patterns
As you can see, different notes come from different places on a guitar, which brings us to the next section:
Near-field placement vs. far-field placement
Ok, so what the hell does that mean? Well, let's do a thought experiment to illustrate this concept:
Think of a tall column of speakers - about 6 feet tall, with woofers on the bottom, midrange speakers in the middle, and tweeters at the top. Now imagine that you walk right up to it and put your ear about 4" away from the system; what will you hear?
If you answered that it depends on whether your ear is near the tweeters, mids, or woofers, you're absolutely right. So where would you hafta stand to hear the whole system evenly balanced? At least 6 feet away is the correct answer - and that 6' away point is the boundry between the "near-field" and the "far-field" in this example. Any closer than 6 feet and you don't hear the whole sound, because you're in the "near field".
Now let's look at a typical acoustic guitar. The body is about 2 feet across. Put a mic any closer than 2 feet and you're in the "near field" of the guitar, and those two links I posted show you that you will be hearing uneven sound, depending on the note being played.
So, the first rule to remember is: "The near field distance is defined as being equal to the length of the longest part of the vibrating section of the istrument."
The second rule to remember is: "Inside the near field of an instrument, the sound will change drastically with different mic placements".
We'll get into mic choices, polar patterns, and mic placements in our next installment, but this "radiation pattern" and "near-field" vs. "far-field" stuff is really important to remember when you're trying to get a good instrumental sound.