Harps are musical instruments that have been used for thousands of years and across dozens of cultures. Because of its widespread appearance in history, countless variations on the harp have been introduced and experimented with throughout the world. Because each harp string is tuned to a specific note, most innovations were developed to find a method to add sharp and flat notes to the instrument's range without making the instrument so large that the musician cannot reach them.
The lever harp tackled the problem of pitches by adding a lever that could be used to increase tension on strings in order to shift their pitch. The lever, which is mounted in the harp's body, is operated by a musician's hand as he plays. Its two-position construction only allows changes between natural notes and either sharps or flats depending upon how the instrument is tuned. While these detuning devices aren't very sophisticated, they're also small enough to keep a harp portable.
The pedal harp builds on the lever harp's basic principal---allowing musicians to shift the pitch of notes by changes in string tension---but applies the theory much more precisely across the harp. Changes in pitch are made using foot pedals, which frees up the musician's hand for full-time plucking. Instead of merely offering two positions, pedal harps function in three positions, allowing musicians to easily achieve natural notes, sharps and flats without having to retune each string on the instrument. Additionally, a pedal is provided for each of the natural notes, so musicians may shift only one set of notes at a time, allowing him to play natural notes on the D strings, sharps on A strings and flats on G strings if needed. These harps' mechanisms are complex enough to require the harp to be large and somewhat immobile.
Also known as a folk harp, lap harps are simple versions of the instrument small enough for a musician to be able to easily carry around. Although some are outfitted with a lever-harp detuning mechanism, many are strung without the ability to shift pitches on each string. This lack of chromatic versatility often lends itself to simpler folk music rather than lavishly orchestrated pieces.
Cross Chromatic and Double Harps
Rather than turning to mechanical solutions to provide additional tones, other harp makers simply added a second row of strings to the instrument. Sometimes, these strings run parallel to one another, as in a double harp, while other times they're strung to cross at a midpoint along the strings, in a cross strung chromatic harp. The extra set of strings provides the pitches to complement the natural notes on the original set, while the cross-strung innovation allows natural and pitched notes to be accessed by either hand.