The simplest voicing for a four note chord is the close position voicing, in which all the notes in the chord are arranged as close together as possible. For example, a C7 chord might be voiced in close position as “C E G Bb”. This is referred to as root position, since the root, C, is at the bottom. The chord might also be voiced in close position as “E G Bb C”, which is also called the first inversion, since the bottom note has been inverted to the top. The second inversion is “G Bb C E” and the third “Bb C E G”.
A drop voicing is created from a close position voicing by dropping one of the notes down an octave. If the second note from the top is dropped, the voicing is called a drop 2 voicing; if the third note from the top is dropped, the voicing is called a drop 3 voicing. For a C7 chord in root position, “C E G Bb”, the corresponding drop 2 voicing is “G C E Bb”. The second note from the top, G, has been dropped down an octave. The corresponding drop 3 voicing would be “E C G Bb”. Drop 2 and drop 3 voicings can be constructed from any of the inversions of the chord as well. On the piano, the dropped note must normally be played in the left hand, so these are almost always two handed voicings. The intervals in these voicings make them perfectly suited for guitar.
Close position and drop voicings are effective when used to harmonize a melody, particularly in a solo setting. Each melody note may be harmonized by a different drop voicing, with the melody note on top. Pianists and guitarists often use this type of approach in their own solos. A phrase in which every note is accompanied by close position or drop voicings is said to be harmonized with block chords. Red Garland, Dave Brubeck, and Wes Montgomery all regularly played block chord solos.