Close harmony

Close harmony is an arrangement of the notes of chords within a narrow range. It is different from open voicing in that it uses each part on the closest harmonizing note (such as - C4, E4, G4), while the open voicing uses a broader pitch array (like - C3, G3, E4) expanding the harmonic range past the octave. Close harmony or voicing can refer to both instrumental and vocal arrangements. It can follow the standard voice-leading rules of classical harmony, as in string quartets or Bach's Chorales, or proceed in parallel motion with the melody in 3rds or 6ths.

Impressionist composers like Claude Debussy and Maurice Ravel often used this voicing in their works and other intervals, such as 7ths, 9ths, and 11ths may be used, since the chords have 4 or more notes and the harmonies are more complex. In jazz, this influence is reflected in George Gershwin's work.

Source : http://en.wikipedia.org/wiki/Close_harmony