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String height, often called action, starts with the distance from the top of the 12th fret to the string at that same fret. A common starting goal is a midrange clearance that feels comfortable and allows expressive bending without buzzing. However, on amplified acoustic guitars, overly low action can invite fret noise and microphonic feedback, while excessively high action demands more force and reduces sustain. The safest approach is to calibrate string height using a precise ruler and a straightedge, adjusting truss rod tension first to set neck relief. After relief is established, tweak the bridge saddle and saddle bedding to bring the string spacing into a balanced, even plane. Test with a medium pick attack to simulate live dynamics.

To determine the proper string height at the nut, measure the gap between the string and the first fret at the fretboard edge. This measurement affects both intonation and how readily the strings vibrate under amplification. Start with a small, incremental decrease in nut height if you notice high frets or rough edge contact. Never shave the nut slots too aggressively; you will create intonation problems and possible binding. When you adjust height, perform a quick harmonic test at 12th fret and then strum openly. A consistent gap across strings reduces unexpected resonance points that can contribute to feedback when a pickup is engaged. Document the exact measurements for future setups.

Pickup spacing influences how the magnetic field interacts with vibrating strings and, by extension, how much of the string’s energy is captured and amplified. On a modern acoustic-electric, the neck pickup can contribute more warmth but also more phase-related feedback if positioned too close to the neck. Conversely, a bridge pickup tends to emphasize brightness and articulation, potentially triggering high-frequency oscillations under stage hot input. The trick is to locate a sweet spot where the pickups capture the core acoustic character without accentuating problematic frequencies. Use a simple alignment method: measure string-to-pickup distance on each string and keep it as uniform as possible, then adjust within a narrow range to preserve balance.

Once you have a baseline of string height and pickup spacing, test in a controlled environment with different playing styles. Play soft arpeggios, loud strumming, and energetic fingerpicking to hear how the setup responds to dynamic input. If feedback begins at moderate volumes, try raising the bridge saddle slightly to increase string vibration damping near the body. Alternatively, reduce pickup height by a small amount to lessen the overall magnetic pull. Remember to recheck intonation after any adjustment because even minor changes can broaden or narrow the harmonic spectrum that leads to feedback. Keep a log of changes and outcomes for repeatable results.

The interplay between pickup height and string height is subtle but critical. Increasing string height can reduce buzzing and relieve fret contact fatigue, yet it may also push the strings toward the pickups, intensifying magnetic interaction and susceptibility to feedback. The opposite holds true when lowering the action: you gain ease of playability but risk louder sympathetic vibrations feeding back through the electronics. A practical compromise is to adjust pickups first, then refine string height. If you notice feedback at a fixed tone, isolate which string or course of frequencies triggers it and adjust accordingly, rather than applying a global change that might degrade overall tonal nuance.

Consider the guitar’s build and the electronics layout. A thicker top, bracing, and internal resonances can exacerbate feedback when the instrument resonates with amplified energy. If the neck is particularly stable, you may experiment with a slightly lower action, provided you maintain adequate tension across the neck to prevent warping. Use a nonstick material to mimic string tension when testing, allowing you to observe the instrument’s natural resonance without overtly amplifying it. In some cases, installing a minor dampening plate or altering internal bracing can improve feedback control without sacrificing tone—though this requires professional service.

For acoustic guitars used with PA systems, the input sensitivity and the preamp’s EQ response play a big role in feedback behavior. A hotter preamp or a boosted high end can quickly create a squeal, especially when a bright, guitar-wide microphone captures body resonance. Start by engaging a gentle high-cut filter on the mixer or preamp to shave sharp harmonics before they reach the speaker system. Combine this with a modest low-end roll-off to keep the body from overpowering the stage ambience. This approach preserves the instrument’s core voice while decoupling excessive energy that can feed back through the microphone and pickups.

Incorporate physical and procedural techniques to minimize feedback. When performing, angle the guitar slightly away from the pickup’s direct field and position it so the body resonates away from the line of sight of the closest loudspeakers. This reduces the amount of energy sent back into the instrument. Additionally, place a light-body contact mic or piezo element away from the bridge area to lessen the proximity of the most reactive zones to the strings. Finally, practice with controlled dynamics; by avoiding extreme strumming at max volume, you allow the electronics to respond more predictably and reduce the chance of feedback during crescendos.

When you adjust string height and pickup spacing, always consider intonation alongside. A common pitfall is focusing solely on the feel and overlooking how fretted pitches drift as you adjust action. If intonation drifts noticeably after setup, the resulting shimmer can interact with amplification to produce unpredictable feedback patterns. Remedy: recheck each string’s saddle position, re-tune the neck relief if necessary, and retest with both clean and driven tones. A properly intonated instrument delivers more accurate harmonics, making it easier to manage feedback with subtle EQ and gain adjustments rather than extreme changes to height or pickup position.

Another key factor is environmental. Temperature, humidity, and crowd-induced vibrations alter the instrument’s resonance and the electronics’ response. In a leaky, hot venue, you may need to raise the action slightly to suppress fret-related overtones while testing the same in a cooler, drier studio space where easier string vibration can demand a different approach. Always recheck your baseline measurements after transporting gear between locations. Engineered consistency helps you anticipate feedback more reliably and reduces the guesswork when adjusting on the fly during performances.

Begin with neck relief and a neutral string height, ensuring a comfortable feel that doesn’t compromise resonance. Then adjust bridge saddles to bring the strings to a level where playability and string contact remain balanced. With these mechanical foundations in place, move to pickup spacing, aiming for even string-to-pickup distances across the treble and bass strings. Finally, perform a controlled feedback test using a variety of playing styles and volumes. Record outcomes, refine individual string adjustments, and repeat the process until you reach a consistent, feedback-resilient voice across the instrument’s range.

After you establish a robust baseline, document it in a setup log for future reference. Include measurements for string height at the 12th fret, nut gap, neck relief, saddle position, and pickup distances. Note the environmental context during testing, including room acoustics and amplifier gain settings. Periodically revisit the measurements because strings settle, wood ages, and electronics may drift. A thoughtful, repeatable routine minimizes the need for dramatic, disruptive changes during live gigs—allowing you to preserve tone while keeping feedback under tight control across venues and situations.