Sound Off: How Guitar Positioning Affects Volume *

Abstract

A concert piano. It's a beautiful instrument and a spectacular sight when it's all set up on stage. The first thing you may notice when you first look at a concert piano is the impressive-looking soundboard, that large board on the back of the piano that is tilted up at an angle. It is used for amplification. The sound board greatly increases the volume of sound coming from vibrations of the strings. The soundboard is positioned so that it gathers the sound vibrations coming from the strings and then retransmits them at an even greater volume when it begins to vibrate. Many instruments have soundboards, including pianos, guitars, violins, banjos, lutes, and harps. Soundboards can even be found in nature. Did you know that you can hear the chirps of little black crickets at night thanks to small soundboards built right into their bodies? Yes, to increase the volume of their chirps, the crickets lift their wings to a 45-degree angle, just like the soundboard on a concert piano!

In this music science fair project, you will investigate how positioning affects the ability of a soundboard to transmit sound. In certain positions there is more damping of the soundboard, which results in a lower amplitude of sound. You will need a personal computer, either laptop or desktop, with a built-in microphone; or a tape recorder with a visual display of incoming signals. If you are using a personal computer, the Bibliography provides a link to free software that will allow you to look at and compare your sound recordings. You can choose any instrument with a soundboard to do your testing, but general instructions are given here for a classical guitar:

1. Sit in a chair a few feet away from the microphone with your guitar.
2. Hold the guitar snugly so that the back of the guitar body is making contact with your chest and stomach, and strum a chord several times. Pay attention to how hard you are strumming, and try to strum with the same force each time. Record or observe the amplitude of the signal.
3. Now hold the guitar in the "folk position" with the bottom of the body resting on your right thigh, and your right forearm and upper right chest contacting the top part of the guitar's body. There should be about 6 inches of space between the soundboard and your torso so that the soundboard can vibrate. Strum the same chord several times again, with approximately the same force as the first time, and record or observe the amplitude of the signal.
4. Now hold the guitar in the "classical position" with the bottom of the body resting on your left thigh, your left foot elevated with a foot stool or books, and your right forearm resting on the top of the body. Tilt the body of the guitar back until it contacts your chest. Again, there should be about 6 inches of space between the soundboard and your torso, so that the soundboard can vibrate. Strum the same chord several times with approximately the same force as the first time, and record or observe the amplitude of the signal.

In which position do you have the least contact with the guitar's soundboard? Which position produced the greatest amplitude of sound?

Last edit date: 2012-12-07

Bibliography

This source describes how soundboards work:

• Wikipedia Contributors. (2008, October 8). Sounding board. Wikipedia: The Free Encyclopedia. Retrieved October 14, 2008, from http://en.wikipedia.org/w/index.php?title=Sounding_board&oldid=243898620

This video link shows the folk and classical guitar positions:

• www.5min.com. (n.d.). How to Play Acoustic Guitar: Sitting Positions. Retrieved October 14, 2008, from http://www.5min.com/Video/How-to-Play-Acoustic-Guitar-Sitting-Positions-2458966

This link provides free "open-source" software with the capability for looking at and editing sound signals:

• Audacity Developer Team. (2000, May). The Free, Cross-Platform Sound Editor. Retrieved October 16, 2008, from http://audacity.sourceforge.net/

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