I heard a very good performance of the Maderna Violin Concerto (1969) on Friday evening with the HR-Symphonie Orchester (there was also a bang-up performance of Punkte, but that's a piece that is almost standard rep for the HR-ers). As well as it was played, the Maderna disappointed because one of the central features of the work, the spatial separation of the orchestra into several sub-ensembles, didn't really add anything to the music and maybe even detracted from it. In the concerto, the soloist is positioned conventially, front-and-center, next to the conductor, there are two bowed string ensembles, one immediately behind the soloist and the other at a distance, there is a plucked string group (mandolin, guitar, three harps), the brass, the percussion, and a wall-o-woodwind to boot. The spatial distribution was limited to positions in the stage proper, everthing directly in front of the audience, with spatial distinctions largely reducible to left-right, and upstage-downstage.
The writing for the violin solist was lovely, with cadenza-like playing overwhelming any concertante playing, which made for a pleasingly unusual concerto form. The problem was that the music for the various sub-ensembles was rather undifferentiated, and distrubuted through the course of the concerto rather too discretely, more in sequence than simultaneously, now this then that, and rarely this against that, rendering any charge the spatial segration might have added rather muted. (In fairness to the composer, a great deal of sequencing and timing in the concerto are decided, ex tempore, by the conductor, so an alternative interpretation might have led to a more pleasing use of resources.)
Asking an orchestra to reposition itself for a single piece in a concert is often a stumbling block to getting a work programmed, so if you wish to have spatial elements in a piece, you have to be able to convince others of the added value of the extra effort. It occurs to me that there might be some general principles of polychoral arrrangements that can be extracted from this experience and might assist in making the case to concert organizers for their utility, necessity, and/or attraction:
(1) If the spatial distinctions are limited — from the audience's perspective — to a single wall, then the differences in the character of the music played by individual groups can usefully be amplified when heard sequentially.
(2) If, however, the ensembles are more physically distinct — again, from the audience's perspective — then more subtle differences in the character of the music played by the separate groups in sequence can be usefully underlined.
(3) If groups are playing simultaneously, however, the more proximate the groups are, the more mixed their sounds will become, thus reducing the separation and clarity of the individual streams in the result polyphony.
(4) when two widely separated groups are playing similar music simultaneously, the effect of the spatial separation can be reduced.