Can you explain the transposing convention in this Jean Sibelius's score?

Question

I am looking at a 1954 edition of Jean Sibelius's orchestral score for Tapiola.

It has the Concert Pitch instruments (Flutes, Violins etc) in two sharps.

He then has various other key signatures which don't seem to match up. For example he has Clarinetto Basso in B, Corni in E, and Trombe in B; staves with no key signature.

Clarinetti in A has one flat; Corno inglesi has three sharps.

So now I'm really confused.

I was expecting that the Bass Clarinet would have a Key Signature of three flats assuming that Clarinetto Basso in B means that it sounds one semitone below written pitch.

Can someone explain what's going on?

I've only read full scores concert pitch so this has me confused.
(Quite apart from the fact that AFAIK Bass Clarinets are Bb.)

Answer 1

The English horn (in F) and the A clarinets have the expected transposed key signatures: concert B minor (two sharps) is written F♯ minor for the English horn (three sharps) and written D minor for the clarinets (one flat).

The "B" instruments are B♭ instruments, denoted using the German system where B♭ is called "B" (B♮ is called "H"). You might therefore expect these instruments to have a C♯ minor signature of four sharps. However, it was traditional for transposing brass instrument parts to be written without key signatures, since they originally always played in their own notated key of C major. Sibelius is perhaps being a bit conservative in following this practice in 1926.

Sibelius also followed the same practice for the bass clarinet in B♭, though I don't have a great hypothesis to explain it. Nonetheless, you can see for example in measure 50, where the contrabass has D and E, that the bass clarinet has E and F♯.

The score is available on IMSLP.