Making an acoustic guitar is a balancing act. On one hand you have structure, and on the other you have sound. The guitar needs to be built strongly enough to resist the string tension and have a long life. It also needs to be built with enough flexibility to produce a warm and inviting tone. Loading the soundboard is one thing you can do to help your new guitar produce the best sound possible.
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Loading the Soundboard for the Best Tone
A soundboard functions like a speaker cone. It moves up and down as the strings increase and decrease in tension. When the string is plucked, it moves side to side. As it moves away, it pulls the soundboard up. When it moves back to center, it releases the pull. Then, as it passes center and goes to the other side, it moves the soundboard up again.
This happens so many times per second that the top feels like it is vibrating, which it is. The constant up and down motion of the soundboard feels like vibration. This vibration is what produces audible sound. However, the sound will only be as good as the ability of the strings to activate the soundboard.
The downside of a plucked or strummed instrument, like an acoustic guitar is in the energy transfer. You only get one chance to impart energy into the system, and that is when you pluck the string. This is the apex of the energy transfer, and it is all downhill from there. The note sounds the loudest and brightest at that moment, then fades away.
Bowed instruments are different. A violin for example derives so much power from such a small structure. Part of the reason is that the bow imparts energy to the string the entire time it is played. This is vastly different from the acoustic guitar. A violin can produce extremely pleasing tones and loud tones because of the constant energy transfer.
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Due to the limitation in the energy transfer of plucked instruments, one thing that is very important is loading the soundboard. This simply means using strings that are powerful enough to apply good torque to the top.
It takes a certain amount of tension to fully activate the soundboard. Very low gauge strings do not pull as hard as heavier strings. The effect is less energy transfer to the top, because lighter strings do not have the same momentum as heavier strings. The heavier an object is, the harder it is to stop when in motion. This is physics 101, and loading the soundboard well by using heavier strings will help conserve energy.
A soundboard requires tension to be pulled up and down and create sound. If too light of strings are used, they do not fully activate the soundboard while at rest. It may be that it takes the first 20%-30% of the strings energy just to overcome the structural resistance, and get the soundboard moving. This means that only the difference (70%-80%) is actually making vibrations that create sound. This is a losing proposition when it takes so much energy to create good sound.
One answer to loading the soundboard well is to use heavier strings. Especially with a guitar that does not have the boom or punch that should be there, heavier strings can drive the soundboard better. There is an upper limit, because overly heavy strings can deform the top over time. However, most players can benefit from going up one level in string gauge.
Loading the soundboard well requires several elements of construction inside the guitar. However, once the guitar is made, using heavier strings can help activate the soundboard to reach its full potential.
Make this small change, and you will notice a difference in your sound. There will be a difference in feel when playing, but it is a small trade for better sound. Heavier strings require more tension to come to pitch. Pressing the string to a fret and strumming will be a little stiffer, but it does not take long to get used to.
Have you ever walked into a room with an acoustic guitar and sneezed? Did you hear the strings vibrate slightly and make noise? If you did, that would be an example of loading the soundboard with the perfect amount of tension. The sonic impact from a single sneeze was enough to create sound from the instrument. Imagine how well it sounds when the strings are actually played. This is an example of nearly 100% energy transfer, and means the guitar will sound the best that it possibly can.
Do you have any questions on loading the soundboard? Leave a comment and I will answer them. Happy building.
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