# AI Wiki - Music - Electro-Acoustic Guitar ## What it is An electro-acoustic guitar (in the US usually "acoustic-electric") is an acoustic guitar with a pickup and, almost always, a preamp built in. Unplugged it is a normal [[AI Wiki - Music - Steel-String Acoustic Guitar|steel-string acoustic]] or [[AI Wiki - Music - Classical Guitar|classical guitar]] (an "electro-classical"); plugged in, it sends a signal to an amplifier, a PA or a recording interface. Wikipedia classes these as acoustic instruments, because the amplification raises the volume without changing the nature of the sound, unlike an [[AI Wiki - Music - Electric Guitar]], where the pickup and amp are the sound. It plays exactly like the acoustic it is built on: same strings, same neck, same feel. The differences are the electronics (a control panel on the upper side, an output jack in the end pin, a battery compartment) and, often, a cutaway, since many are designed for stage use. The hub comparison is [[AI Wiki - Music - Guitar Types Compared]]. ## Pickup systems | System | Where and how | Sound | Feedback resistance | Notes | |---|---|---|---|---| | Under-saddle piezo (UST) | A thin strip under the saddle senses string pressure | Bright, clear, sometimes "quacky" or nasal | High | The most common factory system; needs a preamp | | Soundboard transducer (contact) | Glued or stuck to the top or bridge plate, senses the top's vibration | Fuller, more body and bass | Lower | K&K-style and Taylor Expression-style sensors | | Magnetic soundhole | Clips across the soundhole, senses the steel strings like an electric pickup | Warm, a little "electric" | High | No drilling needed; steel strings only | | Internal microphone | A small mic inside the body | The most natural, includes body resonance | Low at stage volume | Usually blended, rarely used alone live | | Blend (hybrid) | Two systems mixed, e.g. piezo + mic, or magnetic + contact | Combines punch and naturalness | Depends on the mix | The mic can be turned down when feedback starts; the most expensive option | Sources: Premier Guitar ("Your Acoustic Amplified"), Stringjoy, Wikipedia. Premier Guitar found body sensors "not as feedback resistant as piezo or magnetic pickups" and notes that internal mics "often have feedback problems at high stage volumes". Wikipedia notes piezos are the usual factory fit. A magnetic pickup does nothing on nylon strings, so electro-classical guitars use piezos, contact sensors or mics. ## Preamps and onboard controls A bare piezo has a very high output impedance and a weak, harsh signal. Wikipedia: piezo pickups need a preamp built into the body to boost the signal before it reaches the amplifier. Premier Guitar adds that piezos "require a fair amount of preamp gain and EQ" to remove the under-the-string sound. A typical onboard preamp has: - **Volume** and **EQ**: bass, treble and one or more mid bands, sometimes a sweepable mid (useful for cutting the nasal piezo honk). Wikipedia mentions up to six bands. - **Tuner**: a built-in display; many mute the output while tuning. - **Phase switch**: flips the polarity; Fishman's Prefix Pro manual describes it as a tone control at low volume and a feedback filter at high volume, with the best setting depending on the room. - **Notch filter**: a narrow cut you sweep to the frequency that is feeding back. - **Battery**: usually 9 V or AA. A dying battery makes the sound distorted or thin; check it before a gig. Passive systems (no preamp, common with magnetic or retrofitted contact pickups) need an external preamp or a high-impedance input. ## Feedback Feedback happens when sound from a speaker reaches the guitar, makes the top and the air in the body vibrate, gets picked up, amplified and sent back out, louder each time. The hollow body that makes an acoustic sound good is a resonator, and every body has frequencies where it rings most; Premier Guitar describes a player whose guitar fed back mostly on an A chord, at a body resonance near 440 Hz. Low frequencies and boomy notes are the usual culprits. Fixes, roughly in the order to try them: 1. **Turn down** the stage volume or monitors, and stand to the side of the speakers rather than in front of them. 2. **Phase switch**: try both positions at performance volume. 3. **Cut the problem frequency**: notch filter, low-cut, or a narrow cut on the amp or desk EQ. Heavy EQ costs tone, so cut narrowly. 4. **Soundhole cover**: a rubber plug stops the air resonance. Premier Guitar's test found a full cover stopped the feedback but made the guitar "a little banjo-ish"; a vented cover kept more tone and reduced, without eliminating, the feedback. 5. **Change the pickup choice**: rely on the UST or magnetic pickup and turn the internal mic down. 6. **In the moment**: damp the strings with the picking hand, lower the guitar's volume. ## Plugging in - **Acoustic amplifier**: a full-range amp with a flat response, often with a mic input, reverb and a DI output. The simplest setup for busking, practice and small gigs. - **PA through a DI box**: the standard on stage. A DI converts the guitar's unbalanced signal to a balanced, low-impedance mic-level signal that runs over a long XLR cable without hum. With an onboard preamp, almost any DI works; a **bare piezo** needs an active DI with an input impedance of several megohms (the Radial PZ-DI offers a 10 MΩ setting for this; acousticfingerstyle.com explains why a typical mixer input of 1 kΩ or less would choke it). - **Electric guitar amp**: works, but guitar amps are voiced for electric pickups and colour the sound strongly. Wikipedia mentions Kurt Cobain running his acoustic-electric through his pedalboard and amp on MTV Unplugged to keep a familiar sound. - **Recording**: plug into an audio interface's instrument (Hi-Z) input, or better, record with a microphone and blend in the pickup. A mic usually sounds more natural than any pickup; see [[AI Wiki - Music - Home Recording Basics]] and [[AI Wiki - Music - Recording Yourself]]. Acoustic tone through a PA benefits from a little compression and reverb, and occasionally a preamp pedal with EQ and a notch; the general pedal principles are in [[AI Wiki - Music - Guitar Effects]] and amp EQ in [[AI Wiki - Music - Guitar Amps and Tone]]. ## Acoustic-electric vs electric playing acoustic sounds Two different routes lead to an amplified acoustic-like sound: - **An acoustic with a pickup** (this article): real acoustic construction and feel, real acoustic sound unplugged, prone to feedback at volume. - **An electric that imitates an acoustic**: piezo saddles fitted to solid-body electrics, modeling guitars that compute acoustic sounds from the string signal, acoustic-simulator pedals, and thin-body hybrids (for example the Taylor T5 or Fender's Acoustasonic line). They resist feedback and switch quickly between electric and acoustic sounds in one song, but they don't feel like an acoustic: lighter strings, thinner body, and little or no acoustic volume unplugged. For a player who strums acoustic songs and wants to play them on stage, an electro-acoustic is the obvious choice. For a band guitarist who needs a few acoustic-sounding parts among electric ones at loud stage volume, a hybrid or modeling solution avoids feedback. ## Buying and using one - Try it both unplugged and plugged in. Some cheap electro-acoustics put the budget into the electronics and save on the guitar. - Check how easily the battery can be changed and whether the preamp has a tuner and a phase or notch control. - If you only play at home, the electronics add cost and weight without helping; a plain acoustic of the same price may sound better unplugged. - A pickup can be retrofitted to almost any acoustic (soundhole magnetic pickups need no drilling). ## Key Points - Electro-acoustic = an acoustic (steel or nylon) with a built-in pickup and preamp; it plays and sounds like an acoustic unplugged. - Pickups: under-saddle piezo (common, feedback-resistant, can sound quacky), contact (fuller, feeds back), magnetic soundhole (steel only, warm, resistant), internal mic (natural, feeds back), blends. - Preamps provide gain, EQ, tuner, phase and notch; a bare piezo needs a high-impedance input. - Feedback fixes: lower volume, move off-axis, phase switch, narrow EQ cut or notch, soundhole cover, less mic in the blend. - Plug into an acoustic amp, or a PA via a DI; record with a mic when possible. - Electrics with acoustic simulation resist feedback but don't feel like an acoustic. ## Open Questions - Under-saddle piezo vs magnetic soundhole pickup for a home player who records occasionally: which sounds better on a budget? - How much does a good external acoustic preamp/DI improve a cheap onboard system? - Do modeling acoustic simulators (pedals or IRs applied to a piezo signal) now beat traditional blends on stage? ## References - Wikipedia, "Acoustic-electric guitar": https://en.wikipedia.org/wiki/Acoustic-electric_guitar - Wikipedia, "Electric guitar" (section on electric acoustic guitars): https://en.wikipedia.org/wiki/Electric_guitar - Premier Guitar, "Your Acoustic, Amplified": https://www.premierguitar.com/your-acoustic-amplified - Premier Guitar, "Joe's Woes: Acoustic Feedback": https://www.premierguitar.com/joes-woes-acoustic-feedback - Stringjoy, "Acoustic Guitar Pickup Types Explained": https://www.stringjoy.com/acoustic-guitar-pickup-types-explained/ - acousticfingerstyle.com, "DI box" FAQ: https://www.acousticfingerstyle.com/gfaqs/dibox.htm - Fishman, Prefix Pro preamp manual (hosted by Martin): https://www.martinguitar.com/on/demandware.static/-/Library-Sites-MartinSharedLibrary/default/pdf/electronics/prefix-pro.pdf - Sound On Sound, "Radial Engineering PZ-DI" review: https://www.soundonsound.com/reviews/radial-engineering-pz-di ## Related - [[AI Wiki - Music - Guitar Types Compared]] - [[AI Wiki - Music - Steel-String Acoustic Guitar]] - [[AI Wiki - Music - Classical Guitar]] - [[AI Wiki - Music - Electric Guitar]] - [[AI Wiki - Music - Switching Between Guitar Types]] - [[AI Wiki - Music - Guitar Amps and Tone]] - [[AI Wiki - Music - Guitar Effects]] - [[AI Wiki - Music - Home Recording Basics]] - [[AI Wiki - Music - Recording Yourself]] - [[AI Wiki - Music - Playing with Others and Jamming]] - [[AI Wiki - Music - Percussive Fingerstyle]] - [[AI Wiki - Music - Guitar Gear Tips and Tricks]]