A single loudspeaker in a line array can draw up to 24A at 240V [0]. Even a very small rig of 6 speakers would require over 30kw. A 50kw UPS [1] can be purchases for a very affordable $25,000 in 2016 [2]. When building a performance art venue in 1960 or today, a technical ground is a much more suitable option than a UPS.
[0]: http://www.meyersound.com/sites/default/files/leo-m_ds_a2.pd...
[1]: http://powerquality.eaton.com/Products-services/Backup-Power...
[2]: https://store.fgcupssystems.com/products/eaton-93pm-50kw-480...