Tuesday, February 11, 2003

Guitar science 102 - the bodies

I have to wonder just how long people fooled with the design of guitar bodies before they came up with the modern acoustic guitar. There are so many things to get wrong. The type of wood, the aging, the dimensions including thickness, the finish, the gluing and bracing, the size, shape and location of the soundhole(s), the joining of the neck, placement of the bridge....

All of this is critically important in creating the mechanical amplifier that is an acoustic guitar. Variations will deaden the sound, lose the amplification, change the tone or intonation, or might even cause the guitar to collapse under the stress of string tension.

The overall shape of the guitar is intended to be shaped like a woman. Mercifully, they fed their women in those days, and the early guitar makers (known as luthiers because in times of yore they made lutes instead) built them accordingly. Fortunately Kate Moss wasn't around back then. (Although she could have inspired the dulcimer).

Anyway, this complex shape results in complex vibration patterns in the guitar body. The result is a vibration pattern that needs two dimensions to describe it, and it defies neat analysis. The result was that building guitars right required a fanatical attention to detail by people who weren't always sure exactly what they were doing right.

Then along came a guy named Charles Kaman. He was a guitarist and an aerospace executive who possessed the talents and the resources to analyze good-sounding guitars in great detail. By using sophisticated instruments, he was able to determine exactly how good guitars vibrated, and then was able to recreate this behavior in mass production. Eventually he came up with Adamas guitars, with their historically strange body designs and soundhole patterns.

But acoustic guitars were doomed because of their low volume. Big bands would drown out guitars, so they needed sound reinforcement badly. So people like Charlie Christian started using amplification.

Then they ran into another problem. Recall that everything has a fundamental frequency for vibration. As a result, when they are subjected to sounds at this frequency, they start vibrating themselves. Under the right conditions, this "feedback" builds on itself, causing screeches and worse and possible destroying equipment and eardrums.

The amplification of a acoustic guitar depends in part on the guitar's body vibrating readily at the frequencies a guitar produces. Thus they were highly susceptible to feedback when played near their amplifiers. What to do?

Then came Les Paul, a guitarist and recording pioneer. He realized that if you were going to use electric amplification anyway, who needs acoustic amplification? Electric guitars needed to eliminate this vibration as much as possible, and one way to do this was to make the body very stiff and dense. This ultimately resulted in the famous Gibson Les Paul guitar which is manufactured to this day.

Thus the shape of an electric guitar has little to do with its sound. Most continued to follow the general outlines of an acoustic guitar only with necks mounted at a higher fret and cutaways for better access in the high ranges. But then there were Flying V's, Explorers, the Stick, and many more oddball shapes to come.

OK, but how do you amplify them? Stay tuned for guitar science 103 - the electronics.

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