Unlike acoustic guitars, solid-body electric guitars have no vibrating soundboard to amplify string vibration. The string causes the soundboard and the air enclosed by the sound box to vibrate. The audio track includes a mix of both soundboard and taper recordings. The piano has normal strings and hammer action but no soundboard. A harp is an instrument where the strings are perpendicular to the soundboard. Harps' strings rise approximately perpendicularly from the soundboard. It has a large, resonant soundboard made from "Paulownia". It had a soundboard under the strings. Much of mandolin development revolved around the soundboard (the top). Vibrations are transmitted through the bridge(s) to the soundboard. The body has a rounded almond shape with flat or sometimes canted soundboard. Soundboard thickness varies, but generally hovers between . There are braces inside on the soundboard to give it strength. The guitarist uses techniques like strumming ("rasgueado") or tapping the soundboard ("golpe"). The size of the soundboard on a standard modern koto has remained approximately 182 centimeters.