This instr., of very ancient lineage, can be simply defined as an open frame over which is stretched a graduated series of str., set in vibration by plucking with the fingers. In the modern orch. hp. the series is not normally chromatic, as it is in the pf., having merely 7 different notes with the octave, these being in the major scale of B (treated for convenience as that of C♭). There are 7 pedals, each affecting one note of this foundational scale; each pedal works to 2 notches, and by depressing it to its first or 2nd notch, respectively, the vibrating lengths of all the relevant strings are simultaneously shortened by fractions representing a semitone and a tone: thus all keys become possible, and by depressing all the pedals together the pitch of the complete instr. can be raised from C♭ (the normal key) to C♮ or C♯. The usual compass is 5½ octaves from C. Chords are normally played in more or less rapid succession of their notes, in the form understood by the word arpeggio (It. arpa, hp.). The typical ‘sweeping’ (glissando) action of the hand may be used in many kinds of scale (but evidently not in the chromatic scale, nor in any other scale passage employing more than 8 notes to the octave). In addition, of course, single str. may be plucked individually or in small groups. The instr. described above is the double‐action hp., introduced by Érard (c.1810), the word ‘double’ marking its differences from its predecessors on which the pitches could be raised only a semitone.
One earlier form of the hp. is the Welsh harp or telyn, with 3 rows of str., the 2 outer rows (tuned in unison or octaves) giving the diatonic scale and the inner row the intermediate semitones: a simple modulation was effected by touching one of the inner str.
The hp. has been much used as a solo instr. in Wales from time immemorial and in Eng. domestically during the Victorian period. It was a frequent member of the early 17th‐cent. orch. but in later times was rarely found again in orch. use until the 19th cent. when the great Romantic orchestrators—Berlioz, Wagner, Strauss, Mahler, Elgar, etc.—made effective use of it. In the 20th cent. it has been used in chamber mus. (e.g. by Debussy and Ravel). There are several hp. concs.
See also chromatic harp, double harp, clàrsach, dital harp, aeolian harp.