How to Use Multi-pattern Mics on Acoustic Guitar

Date:2020/3/10 9:58:36 Hits:

Acoustic guitars have a place in many musical styles, but the best method of recording an acoustic can vary. The perfect sound for a new-age solo guitar album would likely not be the appropriate sound for a surf record. (Yep, acoustic guitars have long been a part of surf music — listen, for example to the Shadows’ 1960 hit “Apache.”) In any event, acoustic guitar recordings are dependent on many things: the instrument, the strings, the space, the microphones, and most of all, the person holding the guitar. For this article, we’ll concentrate on microphone pattern and placement, leaving the rest for another time.

Cardioid Microphones

If any single microphone placement could be considered a “standard,” it might be a small-diaphragm condenser mic with a cardioid pattern, placed about six inches from the instrument and pointed at the lower bout. The cardioid pattern is more sensitive in front of the microphone with greater rejection of sounds from the sides (and even more rejection from the rear of the mic). Typically, the mic points about halfway between the soundhole and the point where the neck joins the body, a couple of inches below the neck. The biggest reason to avoid miking the soundhole is that the results are usually boomy — pointing the mic a couple of inches to the neck side of the soundhole typically offers a more balanced acoustic guitar sound, with nice highs and good lows. And since boominess has been brought up, we should discuss proximity effect; with directional mics, such as cardioid and figure-of-eight microphones, the closer to the signal source, the greater the low-end build-up. This is not necessarily a bad thing; one of the reasons that contemporary vocalists sing so close to the microphone is that the proximity effect makes the vocals sound “meatier.” It’s the same with acoustic guitars, though defining the low-frequency bump as “meaty” or “muddy” depends on whether you like the effect or not.

The 6-inch distance mentioned at the beginning of the previous paragraph is not a rule, by the way — it’s simply a distance that experience has shown to minimize the bass boost due to proximity effect while keeping as much of the direct signal (versus the indirect reflections that make up the “room sound”) as practical. With some microphones, closer to the instrument works better, while others sound great 12 inches or 18 inches from the instrument. Experiment to find what works best for you.

Omnidirectional Microphones

Since we don’t always get to choose the best recording spaces, there are times when any room sound distracts from the tone of the instrument. To minimize the sound of the room, the goal is to maximize the direct sound of the instrument. But as mentioned earlier, the closer you place a directional mic to the sound source, the greater the proximity effect. For these situations, one handy approach is to use an omnidirectional microphone. The nature of omni mics is that they don’t exhibit any proximity effect, so if necessary, you could put the mic as close as an inch or two from the guitar; there won’t be any low end build-up, and the ratio of direct instrument sound and the indirect room sound is in your favor. There are downsides, of course. The biggest is that while cardioid patterns reject sounds from the sides and the rear of the microphone (to a greater or lesser extent), an omni mic picks up sound from all directions; sounds from air conditioning, computers, even breathing — these will all be picked up. Whether they’re audible depends on how much louder the direct signal from the guitar is than those background noise sounds.

Extreme close-miking is not the only way to use an omnidirectional microphone to your advantage; though. If you happen to have a great sounding acoustic space to record in, you can embrace that sound by moving the microphone away from the guitar — two feet, three feet, or even six feet from the instrument. (A mic preamp with lots of quiet gain will be required.) This type of spacing, more common in classical music circles than in contemporary pop, rock, or country, can be wonderful – if you have a room that can support it. If you do, then consider upping the ante by recording in stereo; a spaced pair of omnis — or, for that matter, cardioid mics in an XY pattern — can sound heavenly. Stereo acoustic guitar miking, however, will be a subject for another article.

Figure-of-eight Microphones

We’ve discussed microphones with cardioid patterns and omnidirectional microphones, but have not talked about the other extremely useable microphone pickup pattern: the figure 8 (also referred to as “figure-of-eight”). Figure-of eight microphones pick up sound equally well from the front and the rear but reject sounds coming from the sides (“sides,” in this case, including the top and bottom of the mic). Figure-of-eight microphones can also exhibit more proximity effect than a cardioid or omni mic, which means that when placed close to the guitar, there can be a fairly large low-frequency boost.

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So how would you use a figure-of-eight to the best advantage on an acoustic guitar? My favorite method is to use the figure-of-eight pattern when recording singers who also play guitar at the same time. By placing the microphone a bit above the guitar’s neck and pointing it at the sweet spot mentioned earlier — and making sure that the top/side “null point” of the mic is pointing at the singer’s mouth, the sound of the voice is minimized in the guitar track. As a side note, using a second microphone (in a figure-of-eight pattern) on the vocal (with the bottom/side pointing toward the guitar) will help to keep the guitar sound out of the vocal track. This allows you to process the guitar sound when mixing without that processing affecting the vocal sound.

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Another approach takes advantage of the figure-of-eight low-frequency boost to enhance signals from less common versions of acoustic guitars. Try a figure-of-eight, for example, on a fretted dobro (8-10 inches above the cone) or on an archtop acoustic (where I’ll usually start with the mic about four inches above the end of the F hole). In both cases, the enhanced proximity response seems to add a nice amount of body to the sound of the instrument.

Summarizing

No single approach to recording acoustic guitars works every time — the properties of cardioid microphones, omnidirectional microphones, and figure-of-eight microphones should be part of your engineer’s tool kit; they’re all both useful and musical.

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