From the August 2018 issue of Acoustic Guitar | BY DOUG YOUNG
One of the appeals of playing an acoustic guitar is the intimacy—that personal experience as the sound washes over you when you’re playing for yourself. Unfortunately, sharing that sound with more than a few others can be challenging. Whether you need to reach an audience in a large concert hall, rise above the chatter at a coffee shop, or compete with drums or electric instruments in a band, making your guitar heard requires some assistance from an amplification system. Figuring out what equipment you need and how to use it can be a daunting task. To help you chart a course through the options, we’re going to look at the big picture and cover the three main elements of an acoustic amplification system: pickups, preamps/DIs, and amplifiers/PA systems.
Where It Begins: Pickups
To amplify an acoustic guitar, we first need to convert its acoustic sound into an electrical signal, which requires either a microphone or a pickup. Mics can be effective in quiet settings, but present challenges when you’re playing loud gigs, or performing in a setting where a mic will also pick up other instruments. In most cases, guitar pickups are a more convenient option, as they allow you to move around, they provide more volume before feedback, and they isolate your guitar’s sound from other instruments. For most of this article, we’re going to focus on systems based around pickups. Although there are hundreds of pickups on the market, they generally fall into several basic types:
Magnetic acoustic pickups are similar to the pickups on an electric guitar. They typically mount across the soundhole, clamping onto the top of the guitar, and in some cases are easily removable. Magnetic pickups are popular among players who need to play at higher volumes because they tend to be more resistant to feedback. They also produce a big, warm—though somewhat “electric”—tone that can be pleasing for many styles. Examples of magnetic soundhole pickups include the Sunrise S-2 ($330), Fishman Rare Earth ($170), Krivo Djangobucker ($199), L.R. Baggs M80 ($249), and DiMarzio Black Angel ($165).
Undersaddle transducers (USTs) are thin pieces of piezo-electric material placed in the slot under the saddle, and are the most common pickups used in factory-installed systems. USTs are, by far, the most popular pickup, owing to their ability to combine good feedback resistance with a reasonable acoustic tone, although they can produce an undesirable sound (often referred to as “quack”) when driven hard. USTs are easy to install and are completely invisible. The Fishman Acoustic Matrix ($167) and the L.R. Baggs Element ($149) are just two examples of USTs.
Soundboard transducers (SBTs) are sensors, usually installed inside the guitar on the bridge plate. SBTs mostly sense the motion of the guitar’s top, and are often described as having a somewhat “woody” tone. In loud playing situations, SBTs can be somewhat more prone to feedback than USTs or magnetic pickups. Examples of SBTs include the Trance Audio Amulet M ($279), the K&K Pure Mini ($99), and the DiMarzio Black Angel Piezo ($119).
Internal mics offer better feedback resistance than external mics, but the sound quality is not as good as that of a mic placed outside the guitar. A few are intended to be used alone, such as the MiniFlex 2Mic Model 1 ($245), but internal mics are more frequently combined with another type of pickup.
Dual-source systems combine two or more different types of transducers in an attempt to reproduce the complexities of an acoustic guitar, or to offer more flexibility. Dual-source systems include the L.R. Baggs Anthem ($299), the Fishman Ellipse Blend ($260, UST plus internal mic), and the Fishman Rare Earth Mic Blend ($289, magnetic pickup plus mic). If you’re adventurous, you can also create your own dual-source system by combining different pickups, even those from different manufacturers.
If you want to amplify anything other than a typical steel-string guitar, there may be other considerations. For example, magnetic pickups won’t work at all for nylon-string guitars, although the other pickup types are all candidates. Resonators have a different saddle geometry that eliminates most standard steel-string pickups; there are a few companies that make specially designed pickups for resonators. Some guitars have unusual saddle configurations, such as Lowden’s split saddle. Guitars with wider-than-usual string spacing or offset soundholes may also limit your options.
DIs, Preamps, and Effects
Most acoustic amplification setups benefit from either a preamp or a DI (direct input) box. At its simplest, a DI consists of an unpowered transformer that converts the high-impedance signal from a passive pickup to a low-impedance signal expected by a mixing board. A DI accepts a standard 1/4-inch guitar cable as input, and supports an output for an XLR mic-type cable that can be run to the input of a mixing board. A DI improves your sound by ensuring that the signal matches what a mixer expects, while allowing you to run a long cable without degrading your tone. Simple passive DIs include the Whirlwind IMP 2 ($53), and the Radial ProDI ($99) or JDI ($199). Some DIs are active, meaning they require power and may include some amplification, such as the Radial J48 ($200) or Samson MDA1 ($35).
The main task of a preamp, either on your instrument or on the stage floor, is to increase your guitar’s signal strength, but most also provide volume and tone controls for shaping your sound, and may include other features as well. Most outboard preamps also provide an XLR output, so that they perform the function of a DI as well. The difference between an “active DI” and a preamp often has more to do with marketing than with function.
A DI or preamp is essential for getting the best sound when plugging a guitar into the mixer of a PA system, and many guitarists prefer to use a preamp even when plugging into an amplifier. Some preamps can also route your guitar to multiple locations. For example, a preamp might send one signal to a PA system and another to your stage amplifier. (Fig. 3) A full-featured preamp can act as a central control point, providing a mute switch, notch filters for feedback control, and more. Some preamps offer effects, tuners, and other useful features not usually found on amplifiers. Preamps also often offer more sophisticated EQ than amplifiers or mixers.
Popular outboard preamps for acoustic guitar include the Fishman Platinum Pro EQ ($299), L.R. Baggs Venue ($299), and Grace Alix ($625). The Tech 21 Acoustic Fly Rig ($299) is an all-in-one pedal board, with reverb, chorus, compression, a tuner, and more, while the Boss VE-8 Acoustic Singer ($299) not only acts as a guitar preamp/DI with effects, but also includes a vocal processor, complete with a harmonizer and pitch correction. Other preamp/DIs, like the Fishman Aura Spectrum DI ($349) or Audio Sprocket’s ToneDexter ($399), promise to improve your guitar sound through modeling techniques.
Amps and PA Systems
The amplification and speaker system you use has a huge impact on what your audience hears. There are two basic options: an amplifier or a PA system, though some products blur the line between the two.
Combo amps are relatively compact amplifiers with built-in speakers. Small amplifiers like the Fishman Loudbox Mini ($329) or Henriksen’s The Bud ($995) are easily transportable and provide enough volume for small venues. Many ampifiers offer a DI output that can be connected to a PA sytem in larger venues (Fig. 2), or you can use a preamp that routes your signal to both the amp and a PA. Either approach allows you to use the amplifier as a stage monitor, while the audience hears the PA.
PA systems usually consist of a mixing board with multiple inputs and relatively large speakers that are placed out front, and may also support monitor speakers aimed back at the performer. A PA system can usually provide higher volume before feedback and can project your music to a larger audience. Smaller PA systems can still be fairly portable, and usually consist of a mixer, such as the Mackie ProFXv2 ($249) or the Allen & Heath ZEDi-10FX ($249), along with a pair of powered speakers, such as the QSC K10.2 ($699 each) or JBL EON610 ($349 each).
There are also systems, often called “Personal PA Systems,” such as the Bose L1 Model II ($2,699 with bass module), Fishman SA330x ($999), or L.R. Baggs Synapse ($1,999), that bridge the gap between amplifiers and PAs. These relatively small systems promise the ability to project to a large audience, like a PA, but can be placed behind you like an amplifier, so the performer hears what the audience hears. (Fig. 1)
Dialing In Your Sound
Once you have chosen some gear, the next challenge is learning how to use it effectively. The first issue most amplified acoustic guitarists encounter is feedback, which can be a problem even in surprisingly low-volume situations. The first step to attacking feedback issues is amplifier placement. A good spot for a stage amp is often on the floor, off to the side, so that your body is between the amp and the guitar (your left side for a right-handed guitarist). When working with a PA system with a wedge monitor, make sure the monitors are not facing back directly into your guitar. PA speakers should generally be well out in front of you. Some guitarists find that a “feedback buster”—a device that plugs up your soundhole—helps to reduce feedback.
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A notch filter on your amp or preamp can usually help you to dial out a problem frequency. To adjust the notch filter, turn up the volume until feedback starts and then turn the notch filter knob until the feedback goes away. Keep in mind that the feedback frequency often depends on your position relative to your amp or speakers, so if you move around while you play, you may encounter different hot spots that you can try to avoid. You may also find that feedback occurs only when you play certain notes, so be sure to check out different bass notes during sound check (if you are able to have one!).
With feedback under control, the next concern is adjusting your EQ to get a good tone. When putting together a system, a great goal is to be able to get a good basic sound with all EQ controls flat, so that the EQ can be used to adjust to different room acoustics and volume levels, rather than to fix the inherent sound of your gear. Guitars tend to have resonances in the lower midrange, which can be problematic at higher volumes. Cutting some bass (60–120 Hz) or low mids (200–400 Hz) can help eliminate boominess. When using magnetic pickups, the electric sound can often be reduced by cutting upper mids (around 1 kHz). With piezo pickups, especially USTs, you may be able to reduce some harshness and quack by cutting the frequencies around 1 kHz, as well as 5–7 kHz. Note that a preamp with parametric EQ controls is useful for dialing in these frequencies; your options will be much more limited if you have only have basic bass, treble, and mid controls.
Your volume levels also affect how your ears perceive tone. At low volumes, our ears don’t respond as well to low or high frequencies. If you are playing at a fairly low volume, you can make your guitar sound fuller by cutting the mids and/or boosting the bass and highs. At higher volumes, you may want to reduce the bass and treble and increase the mids somewhat. If you play in a band, you also need to be concerned with how your guitar sounds along with other instruments. The midrange often ends up competing in a mix with other loud instruments, so a deep midrange-cut may help your guitar stand out.
It is often better to cut frequencies instead of boosting. Cutting instead of boosting can provide more headroom and avoid overdriving parts of your signal chain. For example, if your guitar sound is too dark or is lacking presence, you might cut the bass or lower mids instead of boosting the treble. Your results will vary depending on the characteristics of the EQ controls on your system. Another EQing technique that is especially effective, if you have parametric EQ that allows, is to start by boosting, then adjusting the frequency control to find a setting that sounds particularly bad, and cutting the offending frequency.
You may notice that some of the EQ suggestions here seem contradictory. Dialing in a good sound with an amplified acoustic guitar is a balancing act between volume, tone, and feedback, especially at higher volumes. It helps to learn how boosts and cuts at different frequencies affect your sound, so that you can trust your ears and respond to different situations. The more you use your gear, the better you’ll understand how EQ and other features work. With a bit of practice, you should be able to dial in a good sound quickly, so you can forget about it and focus on the music and your performance.
Active vs Passive Pickups
One major decision when choosing an after-market pickup is whether to choose “active” or “passive.” An active pickup system has a preamp inside the guitar, along with a battery to power the preamp. The preamp may be included invisibly in the endpin jack, or may be mounted on the side of the guitar, along with volume and tone controls. Some side-mounted pickups even include a tuner. There are several benefits to active systems: Besides the possibility of fingertip control over the sound, the preamp buffers the raw pickup element and conditions it to sound its best. This is especially helpful if you tend to plug into a lot of different amplification systems. The vast majority of pickups available today are active, and virtually all factory-installed systems are active.
A passive system has no electronics or battery in the guitar, so it is simpler, which appeals to many players. However, the tone of most passive systems can vary depending on the input impedance of what you plug into. An external preamp can provide a consistent interface and help head off problems. An external preamp may also offer higher quality and/or more flexibility than onboard systems.
Factory-installed Vs. After-market Pickups
Playing amplified is so common that most manufacturers offer guitars already equipped with pickups, and some models are only available with a built-in pickup, often with controls in a panel in the side of the guitar. In some cases, a pickup may be proprietary to one guitar company—Taylor, Takamine, and Maton are a few manufacturers that only offer their own pickups pre-installed in their guitars. Alternately, you can add a pickup to a guitar. Installing an after-market pickup gives you the flexibility to choose the guitar you like and then select your pickup separately, and to experiment with different pickups. On the other hand, buying a stage-ready guitar with factory-installed pickup allows you to experience the complete system before buying, and offers a complete solution designed to work well together.