David Lamkins picked up his first guitar a long time ago. As best he can recall the year was 1967: the year of the Summer of Love. Four decades later David has conjured up an amalgam of folk, rock and jazz solo guitar music for the occasional intimate Portland audience.
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location: Portland, OR USA

Facets: guitars, physics, @musings info

On guitars... a block of wood?

One of my singer friends sent around an Internet mailing titled something like "30 Rules for Rock Bands". Among the rules were gems like "If you enter a Battle of the Bands, you've already lost". And then there was the one: "Guitarists shouldn't change guitars between songs. They're all just blocks of wood with strings, and the amplifier makes all the sound."

Well, maybe... Maybe this is cognitive dissonance at work, but I think there's a difference. We're not talking about subtle subatomic differences that only a physics major could understand, either. Here are some of the things, just off the top of my head, that could affect guitar tone:

  1. the way the guitar vibrates
    1. materials
    2. construction techniques
  2. the way the vibration is translated into an electric signal
    1. the kind(s) of transducer(s)
    2. the location(s) of the transducer(s)
    3. the qualities of the electrical connections to the transducer(s)
  3. the way the electric signal interacts with the rest of the signal chain
    1. tone shaping
    2. distortion
    3. feedback

The guitar is a physical system. Its pieces have physical properties that interact according to the laws of physics. Changing the physical properties of each piece and the way the pieces interact with each other changes the way the guitar vibrates. Changing the way the guitar vibrates changes the way it sounds.

Constructing a guitar is still more art than engineering. A luthier could -- hypothetically -- catalog the effect of each aspect of a guitar's construction upon its sound, thereby turning luthiery from an art into a science. Unfortunately, the number of variables is huge, and their potential combinations are astronomical. So luthiers tend not to stray too far from well-understood formulas for success. Still, there are some well-understood properties of different woods and construction techniques which can -- to a fairly accurate degree -- predict the general tonal characteristics of a guitar.

I want to clear up a potential confusion you may have in your mind about the difference between choice of woods for a guitar and choice of, say, oxygen-free copper cable for your guitar cord. These are both engineering choices; aren't they equally valid? The short answer is: no, they are not equally valid. The vibration of a piece of wood is a physical phenomemon that can be analyzed and measured by instruments that measure the vibration of the entire piece of wood at its interface to the surrounding air. A guitar cord carries the motion of electrons from one end to the other. The amplifier cares only about the change in the number of electrons versus time. How an individual electron travels is of interest only to a theoretical physicist, or to someone who's trying to make a 2,000 percent profit selling wire to gullible guitarists.

The magnetic pickup is the most common kind of transducer used on electric guitars. The ferrous guitar strings vibrate in a magnetic field. Changes in the field are detected by a coil of fine wire and changed into a varying electrical current. Again, there are a lot of possible variations having to do with the strength and shape of the magnetic field (which are themselves determined by the magnetic material and physical construction of the pickups) and with the shape, size and construction of the coil(s). The placement of the pickup affects the quality of the sound because it picks up different harmonic nodes of the strings' vibrations. Even the way the pickup is mounted to the guitar has some effect on the sound, since the vibration of the pickup itself creates a motion relative to the strings; this motion is indistinguishable (so far as the coils are concerned) from the motion of the strings themselves.

Again, pickups are an art rather than a science. People who build pickups are a little more innovative than luthiers (partly because there's less wasted effort if an experiment doesn't turn out well, and partly because pickups are less subject to whims of aesthetics than guitars), but there's still no science of pickup design or placement.

Pickups also have electrical properties. They interact with the guitar's controls, the guitar cord, and the amplifier's input in ways that are predicted by conventional electrical engineering formulas.

The amplifier and speaker adds another set of variables. Some frequencies are emphasized more, others less. Distortion is added, changing the harmonic content of individual notes (in a way that changes with the volume of the note from instant to instant), and altering the sound of chords in more complex ways. And the amplified sound may affect the vibration of the guitar itself, causing feedback. All of these effects are musically desirable. And all of them interact to some extent with the vibration of the guitar and the signal delivered from its pickups.

So an electric guitar is not a block of wood, indistinguishable from other electric guitars only by color and shape. The character of the guitar combines with the amplifier to create a unique sound. The flip side of this coin is that it's difficult to compare guitars -- or amplifiers -- objectively. The sound is created by the whole package: guitar, amplier, settings, and technique. What works well for one player, for one style, may be a disaster for a different player or style.

July 13 2003 08:00:11 GMT