Double flat
Lowers the natural note by two semitones.
What it means
The double flat lowers a natural note by two semitones, that is, by a whole tone. A becomes A𝄫 (German asas), B (German h) becomes B𝄫 (German heses). In sound, the result corresponds in each case to a note that could be written more simply — A𝄫 sounds like G. That the more cumbersome spelling is nevertheless chosen has a reason: the score should show which degree of the scale is meant and where the note goes next. A lowered degree stays that degree in the spelling, even if it coincides with another.
In the notation
It is written as two flat signs standing side by side directly to the left of the notehead. Like every accidental, it applies to the note concerned in its octave register until the bar line. If the double lowering is to be reduced to a single one, in present-day practice a single flat suffices; for complete cancellation there is the natural sign. Older editions know deviating spellings for this, for instance the combination of natural sign and flat.
Musical use
The occasion for a double flat is almost always alteration in a key that already carries many flats. In the remoter flat keys, a lowered degree or a leading tone downward can be written correctly only in this way. It also occurs with secondary dominants and with the diminished seventh chord, whose seventh may require a double lowering. In sequences it makes sure that the pattern looks the same across all degrees.
The double flat is to be distinguished from the double sharp, which acts in the opposite direction, and from the merely enharmonic reinterpretation, in which the note stays the same but name and harmonic sense change.
Other names
Besides Doppel-B (double flat), the spelling Doppel-Be is common; both mean the same sign 𝄫. In German note names the double lowering is expressed by the syllable “-eses”: E becomes eses (E𝄫), B (German h) becomes heses (B𝄫). The sign is cancelled by a natural sign or, if only a single lowering is to remain, by a simple flat, which in older prints is often preceded by an additional natural sign.
Performance practice
Do not play the sign but the sound: first count two semitones down from the natural note and name to yourself the fingering you actually need. On first encounters, note the sounding equivalent small above the note. Take care that the cancellation within the same bar is not overlooked — that is precisely where most mistakes arise.