I occasionally went to concerts in that church in the early 70s. The one that really stands out was a performance of Cornelius Cardew's "The Great Learning", paragraph 7, where the whole audience participates - walking around the nave singing the text at pitches they chose themselves, then every so often walking up to somebody else, listening, and adopting their pitch instead of their own. So the sound started out as an enormous blur and as as a result of all those individual exhanges gradually focused down on a single unison tone.