B flat flat ?

[daz]

I know what a [b]B[/b] flat is, but today i came across what appears to be a [b]B [/b]flat flat?! I was printing out some chord charts to learn when i came to [i][b]C[/b] diminished 7th[/i] and the notes for it were [b]C[/b], [b]E[/b], [b]G[/b]b, [b]B[/b]bb. and the [b]B[/b]bb was in the place where the [b]A [/b]note should be on the finger chart. Whats all that about ?

[jonny-lad]

It's all to do with correct spelling of the notes;

A diminished chord is made up of the intervals tonic, minor 3rd, diminished 5th and diminished 7th...In the key of C, a diminished 7th is 4 and 1/2 tones up from the tonic (9 semitones), rather than being 5 tones (10 semitones) for a minor 7th, or 5 and 1/2 (11 semitones) for a major 7th, [u]but[/u] it is still a 7th, and so is spelt as Bbb rather than A, which would be the 6th.

If it were spelt as the note A, it would take away the option of adding a 6th, or 13th to the chord, like a minor 6th, or 13th (even if it's unlikely to be done), as, in the case of a minor 6th, or 13th, there would be an A and an Ab in the same chord and it would be impossible to notate clearly on a stave.

Hope this makes sense!

[Doddy]

Basically,if you look at chords,you will see that they are generally made by stacking thirds- 1,3,5,7.
(Obviously this isn't always the case,but often it is). In the key of C this would be C,E,G,B.
Now,a diminished chord is made up of the chord tones 1,b3,b5,bb7. So again,in C this would be
C,Eb,Gb,Bbb.
Although the B double flat is enharmonically the same as an A it has a different function. The A
is the sixth(or 13th) of C which in this case, would generally be used as an upper extension. The
B is the 7th,and because it is the seventh note that is double flattened in a diminished chord,it is
written as a Bbb and not an A.

[Major-Minor]

While Doddy's explanation is absolutely spot on (as always !), I have to say that it is very rare to see a double flat or double sharp written on a bass part in the world of rock / pop / jazz. While theoretically correct, it makes sight reading harder, and is really rather unnecessary.
They are fairly common however in the classical and orchestral worlds, particularly in music from the 18th and 19th centuries when being theoretically correct was expected of all composers.

The Major