Cluster voicings pack 3-4 notes within a span of 4-6 semitones — much tighter than any other voicing type. The close intervals create controlled dissonance that adds tension and colour. These are NOT random note clusters — each note has a specific harmonic function within the chord.
Dominant 7th cluster: 3rd + #11 + 5th + b13 (4 notes within 4 semitones). Altered cluster: b9 + natural 9 + #9 + 3rd (chromatic cluster). Dominant chords only — they tolerate the most dissonance.
For colour and tension on dominant chords, especially before resolution. The most advanced voicing technique — requires deep understanding of chord extensions and a confident ear. Use sparingly — clusters are spice, not the main course.