In the winter of 1951 shots from a Colt revolver rang out in St Paul’s Cathedral in an experiment designed to solve the mystery of how architecture shapes sound. In this episode of Holy Smoke, Damian Thompson talks to Dr Fiona Smyth, author of a new book on the subject, and choral musician Philip Fryer, about the perfect acoustic – an increasingly important topic for churches, since many of them rely on the income from hiring themselves out as concert and recording venues. And it raises the question: should we think of a church as a musical instrument?