In
musical (and more spefically,
intervallic) terms, an unequal
fifth is a
perfect fifth followed a
diminished fifth, or the reverse.
Unequal fifths have been the subject of no small amount of debate, but unequal fifths do not fall under the same restrictions that normal fifths do.
As a general rule, all unequal fifths in
voice leading are acceptable unless a diminished fifth resolves to a perfect fifth with these intervals occuring between the
bass and another voice.