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When you start planning a microphone setup for an acoustic guitar in an untreated room, the goal is to reproduce the instrument’s sound as faithfully as possible, while avoiding harsh reflections and muddiness. The process begins with understanding the guitar’s projected tones, from the bright, shimmering top end to the grounded, resonant body resonance. A simple two-microphone approach often yields the most versatile results: a close, dynamic or condenser mic to capture immediacy and detail, and a room-friendly option positioned farther back to register ambience. This method gives balance and flexibility, enabling you to tailor tonal character in post while preserving natural dynamics. Positioning decisions hinge on instrument type, playing style, and room acoustics.

In untreated rooms, early reflections carry substantial influence on how the guitar sits in a mix, so it’s crucial to map out the perceived space around the instrument. Start with a neutral listening position near the guitar and listen for how the room’s walls color the sound. Move the first mic to capture articulation at different strings and frets, testing a few inches of variation to reveal subtle differences in brightness or body resonance. Simultaneously, document how the second mic reacts to room reflections, giving you a sense of whether your goal should skew toward intimacy or ambient spaciousness. This deliberate testing builds a practical mental map before you commit to a final configuration.

The first mic choice should anchor the sound with clarity and presence, yet avoid sounding clinical. A small-diaphragm condenser placed at about 6 to 12 inches above the 12th fret can deliver articulate attack and string detail, especially when the guitarist uses light to moderate picking. If the room produces excessive brightness or hiss, consider lowering the mic slightly or angling it toward the neck for a warmer balance. Avoid direct alignment with the soundhole unless you want boomy low mids; instead, aim for a position where the top strings contribute intelligible sparkle without overemphasizing high-end noise. This balance matters more in untreated spaces.

The second mic serves as a sense of space and body, generally aimed to capture the guitar’s body resonance and the air around the instrument. A small- or large-diaphragm cardioid at a distance of roughly 2 to 3 feet behind and to the side of the guitar often yields a natural blend of room tone with string detail. In narrower rooms, you may find that moving this mic farther back reduces comb filtering and muddiness caused by parallel reflections. Conversely, a slightly closer distance can impart intimacy and presence in a solo guitar track. Always compare both close and room-miked options to determine the most natural combination for your space.

A systematic approach to aroma, presence, and air around the notes begins with documenting reference points in the room, such as chair edges or rug boundaries, which influence reflections. When you place the main mic, use a low-cut filter to minimize proximity-related rumble while keeping the fundamental guitar frequency range intact. The secondary mic’s level should be set to capture the ambiance without overwhelming the direct guitar signal; a gentle blend is often more convincing than a loud room capture. Keep notes on listening angles, distances, and any subtle tonal shifts you notice as you sweep the mics along a horizontal plane, so you can replicate or adjust with confidence later.

Noise management is essential in untreated spaces, where mechanical hums and street sounds can creep into recordings. Use the microphone’s off-axis rejection to limit unwanted leakage, and orient the mics to minimize near-field noise sources like computer fans or HVAC vents. If possible, arrange a temporary acoustic barrier, such as a thick blanket draped behind the guitar area, to break up a few of the most intrusive reflections. While this may not transform the space entirely, it often reduces coloration enough to hear the instrument’s natural dynamics more clearly. Remember that patience during setup pays off in a more usable take later.

The guitar’s own tonal character interacts with mic placement in subtle ways, so expect occasional adjustments to be necessary. A common approach is to set the main mic slightly above the fretboard and angled toward the soundboard to capture brightness and detail without creating excessive brightness at the bridge. If the room sounds overly dark, tilt the mic a few degrees to bring in more upper harmonics. For players with vigorous strumming or pick attack, a slightly closer position can preserve note transient clarity. The key is to remain flexible, testing multiple orientations to identify a position that remains stable across dynamics.

Another useful tactic is to alternate the primary mic position between sessions to reveal how different placements reveal the guitar’s character. For contrast, try a position near the 14th fret and another near the bridge, as these spots emphasize different aspects—edge, sustain, warmth. Document perceptual differences using consistent listening references, such as the same chord progression or piece, so you can quantify which position provides the most natural blend with your room’s accompaniment. The practice also helps you refine your instincts for future setups, especially when room acoustics shift with weather, temperature, or furniture changes.

A robust evaluation method combines direct guitar sound and ambient cues in a single listening pass. Compare the microphone blend against a dry direct guitar signal to assess how much the room color contributes to the overall tone. You should hear natural body resonance without excessive boom, and the highs should remain clear without harsh sibilance. If you notice muddiness, it often points to a reflection-dense sweet spot that needs a retune of angles or distances. Conversely, if the guitar sounds brittle, try a position that adds more body from the room. The objective is to hear a cohesive blend rather than isolated components.

Because rooms are dynamic, you’ll benefit from repeating measurements across different days and with varied playing styles. A consistent approach aids comparability and helps you recognize which elements of your setup are genuinely robust versus those that only work under specific conditions. Maintain a simple log of mic positions, distances, and observed tonal changes, enabling straightforward replication when you or another engineer revisits the session later. This practice reduces guesswork and yields more repeatable results in future recordings, especially when you need to scale the rig for different guitars.

Ultimately, the best microphone placement for an untreated room balances realism with practicality. Favor a core setup that yields an intimate listen while preserving enough ambience to carry the guitar’s natural sustain. If you must compromise, prioritize midrange clarity and a smooth high end over ultra-detailed brightness, which can fatigue the listening listener in longer sessions. The aim is a natural-sounding guitar that feels alive, not an overly polished capture. Use headphones or a trusted monitor system to confirm your impressions, and adjust only when the differences are meaningful to the track’s mood and genre.

As you gain experience, you’ll automate many of these decisions and develop a sense for what works in particular spaces. Your process should remain data-driven yet flexible, because acoustic reality rarely adheres to a single formula. Record with curiosity, compare with fresh ears, and keep experimenting with positioning and room setup. The most enduring placements are those that consistently deliver the guitar’s true character without demanding expensive treatments or exotic hardware. With patience, you’ll create natural, musical performances that translate well to different listening environments, from home studios to modest rehearsal rooms.