Transposing bass clef instruments for Tuba, Bombardon, and Contrabass

You're fortunate in this case in that everyone's playing a concert Ab. So you can work out the transposition theoretically, then check your result empirically!

I guess you're familiar with 'Trumpet in B♭', 'Horn in F' etc.? Don't be thrown off by being in bass clef. It's the same thing. Play a major 2nd down for instruments 'in B♭' (because B♭ is a major 2nd down from C).

I suspect the bottom two instruments in your score sound a further octave lower than written.

Here's some further explanation:

https://www.vsl.co.at/en/Bass_tuba/Notation

It’s like Brian explains: all bass parts are identical, playing Ab in concert pitch.

There’s a trick for Eb Bass players reading treble clef:

Take the part for double bass, read as it were treble clef (just replacing the bass clef by a treble clef) and ignoring 3 flats: bass clef = treble minus 3 flats!

So the written Ab for double bass is read as F for Eb Bass in F major key (F => Ab transposed by the Eb-Bass.

Sibelius doesn't know about Bombardons, but the important thing is to look at what follows the instrument name, e.g. "in Es" or "in Bes", which mean respectively "in E flat" or "in B flat".

In the snippet below, all three instruments are sounding a concert C. Double bass is non-transposing. E flat bass performs A natural to sound a concert C, and B flat bass performs D natural to sound a concert C.

So if you read the B flat bass part and transpose down a tone you get concert pitch. And read the E flat bass part, transpose up a minor third to get to concert pitch.

British Brass Band has B flat and E flat basses but written in treble clef. Only bass trombone is written in bass clef, and that's at concert pitch. I've not come across transposing bass clef parts like these before.

Here are some staves that show the notes the various brass band instruments perform and the corresponding sounding concert pitches: