A double-flat is the equivalent of two flats, and lowers a note’s pitch by two half steps. The double-flat symbol (♭♭) is placed before a note like other accidentals.
- Exceptions to this are Fb and Cb, which point to the E and B natural keys, respectively; and Fbb and Cbb, which are the Eb and Bb keys.
The Purpose of the Double-FlatDouble-accidentals are not seen in any working key signature. In fact, if there were a key signature after Cb major (which has the maximum seven flats), it would contain a B double-flat (learn more about theoretical key signatures).
But in everyday notation, double-flats are necessary in certain scenarios. Suppose you were composing in the key of Cb major (which puts a flat on every note) and wanted to write a G natural in a measure or passage containing a lot of Gb’s. Instead of alternating between writing G natural and G flat, you could indicate the tone of G by writing an A double-flat instead.
See (x) double-sharp.