Acoustic guitars are made from a variety of different woods whose natural resonance is characteristic of their individual shapes and materials. In addition to the sound of the strings resonating inside the body of the guitar, the sounds of the player’s fingers on the fretboard are often an important and desirable component of the recording. This “fret sound” is considerably different on nylon-string classical guitars as opposed to steel-string acoustics, though the tone can also vary greatly from brand to brand for the same type of string.
When using one microphone, a cardioid polar pattern generally yields the best result by allowing for a combination of sound from the guitar’s soundhole and fretboard. Large diaphragm mics may work well for recording acoustic guitars in some situations, but medium diaphragms are often preferred in order to reduce the proximity effect that results from aiming the microphone capsule towards the soundhole. Proximity effect in this application can be perceived as a lack of intelligibility or “muddiness” in the low-mid frequency range.
The most popular position for mic’ing acoustic guitars is where the neck joins with the body. Positioning the microphone here results in a nice balance of warmth from resonance of the wood, along with the brightness and sheen of fret sound and finger noise. (See image “K”.) Deploying a pair with one mic at the joint and the other at the bridge can result in one of the most satisfying acoustic guitar sounds. (See image “L”.) Panning one track hard left and the other hard right during the mixing process can yield a dramatic stereo sound.
Mic’ing the bridge of the guitar yields a brighter sound with more attack as a result of the propensity of string resonance off the body of the guitar. Angling the microphone either away from the sound hole or tilted up from underneath can achieve this effect. Be careful to consider the movement of the player’s strumming hand when positioning the microphone as it can interfere with direct sound reaching the microphone. Careful placement for this technique is usually well worth the additional effort as it impressively captures the guitar’s natural acoustic balance.
Close-mic’ing techniques often create more presence than is desirable for acoustic guitar. Placing the microphone three to four feet in front of the performer and level with the sound hole in order to capture more room sound will typically generate a more natural sounding recording. To create more of a concert ambience, deploy a pair left and right at even greater distances. You can also attain the best of both worlds by using multiple microphones to combine the aforementioned close-mic’ing techniques with this distance-mic’ing technique.