For recording a singer playing acoustic guitar, a figure-8 mic with its null point aimed at the guitar is often effective. This arrangement picks up mostly vocals and minimizes leakage from the guitar. Optionally, you can use another figure-8 mic with its null point aimed at the singer to pick up the guitar and reject the vocals.
Mic selection and placement are obviously very important considerations. If you're fortunate enough to have access to an expensive large-diaphragm tube condenser mic-such as the venerable Neumann U 47, the silky AKG C 12, or the divine Telefunken Elam 251-you certainly have an advantage. But even a classic mic doesn't guarantee a great vocal track.
Anyone who has recorded more than one vocalist knows that no one mic is perfect for all vocal applications. One singer will sound great through a certain mic, while another sounds like a cat caught in a blender. Why? Because all voices are different. There are certain truisms in the studio; particular mics tend to work well on female voices, while others tend to work well on deep male voices, and so forth. But given the time and resources, you should try a variety of combinations. You'll be surprised with the results.
Here are some questions you need to ask before choosing a mic. What overall sound do you want in the track-warm? clear? present? intimate? edgy? thin? Which qualities in the singer's voice do you want to accentuate, and which do you want to minimize? What is the singer's dynamic range? Does the singer have good mic technique, avoiding excessive plosives and either staying in one place so that the sound doesn't vary or moving back and forth to adjust for volume changes?
I want to dispel the myth that large-diaphragm condensers always make the best vocal mics. Sometimes they do, but often they don't. Small-diaphragm condensers and moving-coil and ribbon-dynamic mics can sound incredible on the right singer. In fact, many of the revered vocal performances of the 20th century were captured by ribbon mics. Keep an open mind, and trust your ears.
Many singers who have spent a lot of time in the studio know what mic (or mics) sounds best for them. It's a good idea to ask singers which mics they have used successfully in the past-it can save you a lot of trouble. Some singers will even ask ahead of time for a particular mic. Appreciate it when it happens, because you're likely dealing with a pro who has a good understanding of the recording process.
Otherwise, if you have a lot of experience and know the sound of your microphones, you can often guess which one will complement a particular singer for a particular application. For instance, for a singer with a nasal voice, I probably won't use a Neumann U 87 (a standard choice for vocals), because its midrange peak will tend to exaggerate the worst qualities of that type of voice. Instead I might use a ribbon mic or even an EV RE20 (which is a large-diaphragm dynamic).
Furthermore, I might not use the same mic from track to track. An intimate ballad with a detailed sound and the singer performing close to the mic calls for a different mic than the one I would use on a rock song with belted-out vocals. Some mics don't respond well to high sound-pressure levels, and many singers' voices change timbre when they change their delivery. You need to consider all the details to make the best mic choice.