My symphonic piece has a passage that requires four independent lines from the trombone section. Since brass instruments can't play more than one simultaneous note, this requires four trombones. I don't see the presence of 4+ trombones in most symphonic literature(Mahler broke this barrier a lot, but Mahler can get away with virtually anything). With the assumption that this gets performed, it will probably not be by a professional orchestra, more likely a high school-college level orchestra. Is it generally reasonable for a composer to expect a non-professional orchestra to have four trombonists?
Is there a good reason that the lowest line can't be played by on a tuba?– Elements in SpaceFeb 26 at 9:12
@ElementsinSpace The passage wanders tonally, and the bassline has some chromatic motion(Which, from my understanding, is not easy on a tuba, correct me if I'm wrong).– OprenSteinFeb 26 at 9:27
2@ElementsinSpace tuba isn't any less capable of achieving chromatic motion than trombones are– nuggetheadFeb 26 at 12:23
Why not simplify it to three trombones and get the horns to cover one of the inner voices. Or get trumpets playing in a low register to cover the top trombone part. Or get a combination of woodwinds to cover one of the inner voices. You'd be surprised what you can get away with!– Brian THOMASFeb 26 at 15:01
My experience is that at the high-school level, it would be extremely unusual. Even having trombones can be the exception, as it many school settings the orchestra is a string ensemble — maybe with woodwinds — but the brass and most wind players will be in the symphonic and/or marching band. Even the ones that do have trombones are unlikely to have four.
At the college level, orchestras tend to follow the symphonic model, but especially at a music school, they would at least have better access to auxiliary trombonists.
The standard 'symphony' orchestra has 60+ players including three trombones and one tuba. And two flutes, one doubling piccolo. And four french horns. etc.
And it's very unlikely that a high school orchestra will have this exact setup. What country are you in? If it runs the American pattern, the music program is likely to centre on marching band plus maybe a wind ensemble. There may be a plethora of trombones available, or a shortage. If there IS an established 'symphony' orchestra will an extra trombonist want to attend just to play in one piece?
Looking at previous comments, yes, there's always the tuba. And it's just as chromatically agile as a trombone, maybe even more so! There are no tricky slide shifts on a valved instrument!
But this IS a high school orchestra. You have to work on the assumption there MIGHT only be three trombones, might not be a tuba... Cross-cue this section in horns, trumpet, bassoon... It won't be quite what you envisaged, but at least the notes will get played!
The standard trombone section in an orchestra is three players. Asking for four is going to greatly reduce the chance that your piece will be played. Almost all orchestras will have a fourth trombone available if they decide to play your piece (in a professional orchestra this costs money). More likely they won't bother.
Things are different for an established composer (which you are presumably not). If you're John Williams, you can get as many trombones as you want.