Custom Transpositions (tubas)

Could somebody help me with making custom transpositions?
I want a Bass Tuba in Bb.
Is there a way to do it without going to Layout overrides and doing it for the project?


What do you need this for, I wonder? As far as I have seen, bass tubas are not transposing instruments. The horn itself may have a fundamental pitch of C or B♭ or other, but they (along with trombones) are always written at concert pitch.

Music for tenor tubas and Wagner tubas in F, B♭, etc. is transposing, but I have not heard of a transposing bass tuba in B♭.

Gotterdamerung has Bb Bass Tuba and Eb Tenor Tubas.
I know they are not usual instruments, but having the option would be great.

Yes, so those are the Wagner Tubas. You may want to change the names after you put them in.

Standard (British style) brass bands treat all instruments, except the bass trombone, as transposing instruments in treble clef. So the BB♭ bass tuba (informally referred to as “the double B”) is written in treble clef but sounds two octaves and a second lower than written. Some European band music also has parts for E♭ and BB♭ tubas written as transposing instruments in bass clef - you occasionally come across this in late Romantic orchestral music with bass clarinet and bass trumpet parts written in bass clef but transposed.

In the instrument picker, Dorico has an option for BB♭ tuba in treble clef (at least in the part). It is under Brass > Bass.