Electric guitars typically do not need this set-up to be heard, though there are acoustic-electric guitars. Instead of vibrating a saddle, the vibrations of the strings are detected by a series of pick-ups, which transfers the sounds through electronic circuits, giving you the ability to alter the volume and tone color of the sound before it is output to the amplifier. The guitar in this illustration is partially hollow and has a small hole in the top on the left side, called an f hole because of its shape. This guitar will be audible when it is played without an amplifier, but it will not be very loud. Electric guitars with a solid body are typically very quiet and unusable when played without an amplifier. One of the characteristics of solid body guitars is their sustain. Their hard wood body typically causes strings to vibrate longer.