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Microphone Month

How to get the best recorded acoustic guitar sound. Part 2: Selecting the mic

The first part of this series was all about preparation, which is half the battle. To reiterate, once the guitar sounds good to both you and the performer (or just you if you’re doing it yourself), then you’re ready for mic selection.

Large professional studios will have a broad range of different mics to choose from, but many home recordists are faced with a much more limited choice, so the decision is usually fairly straightforward. The first thing to realize is that there are few dynamic mics capable of doing justice to the acoustic guitar, other than perhaps the Sennheiser 441, because of their inherently limited high-frequency response. High frequencies are vital to acoustic guitar sounds, and therefore you’ll probably need a condenser mic to get the best results, as these are more sensitive and pick up much more high-frequency detail. (One mic we’ve had enourmous success with at Sweetwater Studios is the Royer R121 ribbon mic, but again, this series is primarily for the budgetary-challenged.)

Whether you choose a true capacitor model or a cheaper, back-electret design may well be determined by your budget, though manufacturers such as Studio Projects, Rode and Audio Technica are now making capacitor designs available at ridiculously low prices. This is not to say that back-electret mics aren’t capable of turning in a good performance, but be aware that those models that are powered by batteries may have lower sensitivity and headroom than those models which will only run off phantom power — some are little more sensitive than a good dynamic mic!

Purists will often pick a small-diaphragm capacitor mic for its greater high-frequency accuracy, and one with an omni polar pattern for a more transparent sound than can be achieved using a cardioid. However, if you’re one of the many people who have one or two large-diaphragm cardioid mics only, that doesn’t mean that you should have trouble getting good results. For a start, omni-pattern mics usually require a recording room which sounds significantly better than most home studios, so a cardioid pattern will usually suit smaller rooms better.

Whichever mic you choose, the positioning of it is crucial. In a live situation its normal to see mics placed very close to the sound hole of an acoustic guitar, because the important considerations are level, separation, and the avoidance of feedback. In the studio, however, you’re after a more natural sound, and such miking is therefore less useful. It is true that a lot of the sound energy of an acoustic guitar comes directly out of the sound hole, but much of that is heavily colored by the body resonances of the instrument. This boxy and boomy sound usually needs heavy EQ’ing to render it usable even when playing live, and this really isn’t the way to go when recording. If you’ve got your guitar sounding right at source, you shouldn’t have to be using drastic processing during recording.

Natural guitar sounds balance the different vibrations from all over the instrument with each other, and with sonic reflections from the player’s surroundings. If a mic is used too close to the guitar, the direct sound from the part of the instrument it is nearest to will dominate the sound from other parts of the instrument and from the room. You risk miking up only a part of the instrument when what you’re really after is the bigger picture.

On the other hand, if your mic is too far away from the guitar, you can end up with a lot of room ambience, leaving the original sound distant and unfocused. You may also find that your mic exhibits unacceptable levels of noise when you apply the level of preamp gain which distant miking requires, especially if you’re using a less sensitive model.

As for the specifics of mic positioning, a common approach is to set up the mic around 16″ (40cm) from the guitar, with the capsule aimed at the point where the guitar’s neck joins the body. This will usually produce a well-integrated sound — the levels of direct and reflected sound will be about right, and the sound hole’s contribution will be controlled because the mic doesn’t point directly at it. If you have a pair of enclosed headphones, then you can easily experiment with tweaking this mic placement while listening for the best sound. If you find a promising sound in this way, remember to check it out on your monitors before committing yourself — headphones can sometimes be rather misleading. As a general rule, moving the mic further towards the neck will brighten an excessively bassy sound, while moving closer to the sound hole will bring more warmth and fullness to the sound. Moving the mic further away from the guitar will increase the proportion of room ambience overall, while moving in further will dry the sound up. Alternatively, if you like a closer-miked sound, but would prefer more room ambience with it, try using an omni-pattern mic (Earthworks QTC or TC series mics provide excellent results) instead of a cardioid, if you have one.

Even though the basic mic placement described above is by far the most commonly used, it doesn’t always produce the best results. For example, if you’re after the sound that the guitarist hears, then a single mic or a pair of mics set up to look over the player’s shoulder at about head height can often capture a convincing tonal balance, particularly when using a large bodied guitar that is excessively boomy miked from the front. It can also be educational to point the mic in even less obvious directions, such as at a nearby reflective surface, or even at the underside of the guitar. Such alternative placements are often quick to try if you’re wearing headphones, and can sometimes turn up a brilliant sound that no amount of theory would have predicted.

In the next part of this series, we’ll discuss setups using more than one mic, but for now, there’s more than enough to play with. However, since our policy is better more than less, here’s on last insider’s tip for the road. It’s called Nashville Tuning, which is one way to get a bright, jangly acoustic guitar sound, which can cut through cluttered pop mixes. In Nashville Tuning, the bottom three strings of a conventional steel-string guitar are replaced with strings designed for the upper three positions. The new strings can then be tuned to pitches one octave higher than the strings that they replaced. See you in part three, “Using More Than One Mic.”

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