The top or belly (and often the back) of the archtop guitar is either carved out of a block of solid wood or heat-pressed using either a solid top or laminations, the latter being a less expensive construction method. The belly normally has two f-holes, the lower of these partly covered by a scratch plate raised above the belly so as not to dampen its vibration. The arching of the top and the f-holes are similar to the violin family, on which they were originally based. The contours of the arching profile are usually derived in an ad hoc fashion. The tops of Gibson's archtops were parallel braced. X-braced designs were introduced later, giving a tone closer to that of a flat-top guitar. Sitka spruce, European spruce, and Engelmann spruce are most often used for the resonant tops of archtop guitars, although some guitar builders use Adirondack spruce (Red spruce), or Western red cedar. Archtop guitars often have Curly maple or Quilted maple backs. Full-sized archtops are among the largest guitars ever made, with the width of the lower bout in some cases approaching 19 inches (47 cm).