It’s inevitable that any performing acoustic guitarist will have to consider amplification, but the glut of options can make it hard to find the right setup for your situation. This is the first in a series posts I’ll be doing that aim to shed some light on various aspects of acoustic amplification.. This particular article will cover the differences between the common pickup types and their strengths and weaknesses. It will also look at what modifications would be necessary to add it to an instrument after-market.
The most common acoustic pickup elements use piezo crystals transducers (piezo, from the Greek word piezein for “to squeeze”). When pressure is applied to quartz crystals they produce a small amount of voltage. In a pickup, the guitars vibrations are turned into an electrical current, which an amplifier then turns into sound. There are two types of piezo pickups; Under-the-Saddle and Souudboard Transducers.
These are the most commonly found factory-installed acoustic guitar pickups, and offer some of the best all-around performance. As the name suggests, they sit beneath a guitar’s saddle; the small strip of plastic or bone on which the strings rest on the body of the guitar.
Because these pickups don’t take vibration directly from the guitar’s top, they are highly feedback resistant. But this means that the signal is derived more from the vibration of the strings rather than the body of the guitar. This makes them ideal for high volume environments, but less than optimal when one desires a transparent representation of a particular instrument’s tone.
Installation of this type of pickup requires a small hole to be drilled through the bridge and top of the guitar for wiring, as well as widening the endpin hole to accommodate a 1/4″ jack. In addition, the saddle must be shortened or replaced to compensate for the thickness of the pickup element.
This style of pickup attaches to the underside of the guitar’s top and usually gives a more accurate reproduction of the instrument’s natural tone. Unfortunately, they are more likely to feedback than undersaddle or magnetic pickups.
Soundboard transducers are fairly non-invasive to the guitar, needing only the installation of a 1/4″ endpin jack. The pickup itself is mounted internally on the underside of the bridge with an adhesive, putty or double-sided tape. Though, I know of at least one brand of pickup requires that it be superglued to the the bridgeplate, meaning that de-installation destroys the transducer elements.
It is possible to temporarily mount this style of pickup to the outside of the guitar. This means the instrument can be amplified with no permanent alteration to the guitar, but the trailing cable often causes noise as the guitar shifts during performance.
Soundhole Magnetic Pickups
Technically, this is the oldest style of acoustic pickup as it is essentially the same basic design found in electric guitars. They consist of one or more magnets wound in copper wire. Mounted in the soundhole, the strings of the guitar pass through the pickup’s magnetic field. When the strings vibrate, the pickup turns the disruption into an analog audio signal.
Though these pickups are the least susceptible to feedback and the easiest to install, they have the least acoustically accurate sound of any of the pickups described here. Because the sound is derived solely from the strings interaction with the magnetic field, the acoustic properties of the guitar or the strings never come into play. This is can be good for high-volume live shows, but if you want a pickup that more closely represents your guitar, you should choose a soundboard transducer or an undersaddle pickup.
Usually, these can be installed with little impact on the instrument. A hole for the endpin jack is required, but the pickup itself usually clamps in place and has foam pads to protect the guitars finish. On higher-end models, there may be adjustable pole pieces. This allows one to adjust the volume on each individual string.
Again, these can be mounted with no alteration to the guitar by trailing the cable out of the soundhole. But unlike the soundboard transducer, they tend to produce little to no noise when jostling the cable.
So… What now?
Well, pickups are great. And you’ve got a lot of options if you’re looking to install one or know what you’re getting if you buy an instrument with something already on board. But what if you need to record?
That’s where microphones come in. While you can make great recordings with a pickup, you often get awesome results with even an inexpensive mic and a little know-how.
So, next time we’ll be talking about microphones for both recording and live performances.
A version of this post was previously published on the website of The House of Musical Traditions.