In my work with touring shows still playing on Broadway.... big production numbers don't get individual vocal mics in foldback but some more intimate scenes/number might. In the Green Witch musical the numbers featuring duos tend to get *some* star mics in foldback; in the Mrs. Dictator in Argentina I don't recall any vocals in
stage foldback, but that was in the tour from 15 years ago so things may be different today.
The
Mouse's Big Kitty show had more lead vocal foldback than I've noticed in other shows - it wasn't particularly loud but tended to create a 'big' sound on
stage. Lots of playback/SFX in the foldback in that show, too.
I have a fairly dim view of vocal foldback in musical theater, partly for technical reasons but most of it is based on my artistic belief that actors should "learn their craft, practice and rehearse it." Singing is part of that craft (as is rudimentary dance) and the skills necessary to sing well, to sing with projection and diction, to sing correctly (to minimize throat damage)... all can be taught and coached. Actors - and theater in general - would be better served if we didn't have to rely on technology to deliver what the talent is insufficiently trained for. On the tech side, since all the foldback levels, input EQs, muting and unmuting,
etc rely on consistency of execution, the talent has to be spot on as the show mixerperson simply doesn't have time to tweak the foldback. Then there is the management of expectations - once you start putting 1 actor in foldback you'll find that other actors now "need" to be in the mix, too. They'll say they don't sound as loud as the amplified actor and while that's possibly correct, what is certain is that now the sound on
stage sounds significantly different to the actors and they really, really need to be performing in the same "sonic space" to keep their heads from exploding trying to make sense of the conflicting aural cues.
Finally, what does the actor genuinely need to hear on
stage, and how much? If the actor cannot hear him/her self over the
orchestra/band, that's a music direction issue as
Loudest Sound At The Mic, Wins! Putting that actor's mic in foldback will amplify the excess
orchestra, too. Perhaps a little, perhaps a lot,
book and score dependent, but it's gonna happen. OTOH, if having 2 actors on opposite sides of the
stage need to hear each other, a little cross-stage foldback is entirely appropriate. And now that every light over the
stage has motors and fans inside, the
base level noise floor has come up at least 6-9dB and much of it in the spectrum where it competes with critical midrange. We amplify that, too.
Optional Story-
Around the turn of the century (the most recent one) there was a touring show of Dry Ice
Fog, tap dancing, and possibly leprechauns. The band/
orchestra was on
stage and their foldback was mixed off
stage left (in music concert tradition) on a hernia-inducing amount of Cadac M. Every interval and after every show the musicians would swoop down on unfortunate
monitor mixerperson. Nobody was happy with anything. You'd think he stole their pot of gold or pissed in the Lucky Charms. At any rate the final indignity was that the live performance audio sources were the back up for the Otari RADAR
system (except for solo vocal performances, which were live as primary). Absent a technical failure, what the audience heard was not what the musicians were hearing and fighting over. Over and over. Eventually they flew in the Sound Designer for a refresh and the confrontations seemed to abate.