A soundboard is the surface of a string instrument that the strings vibrate against, usually via some sort of bridge. Pianos, guitars, banjos, and many other stringed instruments incorporate soundboards. The resonant properties of the soundboard and the interior of the instrument greatly increase the loudness of the vibrating strings. "The sound board is probably the most important element of a guitar in terms of its influence on the quality of the instrument's tone [timbre]."When the [guitar] top vibrates, it generates sound waves, much like a loudspeaker. As the soundboard moves forward, the air that is in front of it is compressed and it moves away from the guitar. As the soundboard moves back, the pressure on the air in front of the guitar is reduced. This is called a "rarefaction," and air rushes in to fill the rarefied region. Through this process, an alternating series of compression and rarefaction pulses travel away from the soundboard, creating sound waves.

In musical instrument classification, string instruments or chordophones, are musical instruments that produce sound from vibrating strings when a performer plays or sounds the strings in some manner.