Read The Sound Book: The Science of the Sonic Wonders of the World for Free Online Page B

in a line—the idea being that the sound from the loudspeakers adds together to beam the speech toward the audience. More modern systems use sophisticated signal processing to electronically alter the sound coming out of each loudspeaker, creating an especially narrow beam of speech concentrated only on the congregation. 3 5
    Whereas large churches are something of a nightmare for speech, they make wonderful performance spaces for organ music, as author Peter Smith writes: “The melody line is dominant, but its chords are sounded against the surviving strains of the preceding chords in declining strength. The result is a measure of clash or discord that adds considerable piquancy to the experience. There is a richness . . . in a great cathedral which is absent from the concert hall.” 36
    Churches had a profound effect on the development of music. St. Thomas Church (Thomaskirche) in Leipzig, Germany, is an important example. Before the Reformation, the priest’s voice took 8 seconds to die away in the church. In the mid-sixteenth century the church was remodeled to help the congregation comprehend the sermons. Wooden galleries and drapes were added that muffled the reverberation, dropping the decay time to 1.6 seconds. Moving forward to the eighteenth century, we find one of the cantors, Johann Sebastian Bach, exploiting the shorter reverberance to write more intricate music with a brisker tempo. Hope Bagenal, the senior acoustic consultant of the Royal Festival Hall in London, considered the insertion of galleries in Lutheran churches, which reduced reverberation, to be “the most important single fact in the history of music because it leads directly to the St Matthew Passion and the B Minor Mass.” 3 7
    How reverberant are grand cathedrals? St. Paul’s Cathedral in London was built between 1675 and 1710 to replace the predecessor, which had been destroyed in the Great Fire of London. Designed by Sir Christopher Wren, it has a vast volume of 152,000 cubic meters (5.4 million cubic feet). At midfrequency, the reverberation time is 9.2 seconds; at low frequency it rises a little, to 10.9 seconds at 125 hertz. 38 These decay times are long, but at low frequency the Hamilton Mausoleum is more reverberant, probably because it has fewer windows (which are quite good at absorbing low frequencies). The values at St. Paul’s Cathedral are typical of other large Gothic cathedrals, so the mausoleum appears to beat the sanctuary in terms of reverberation.
    W hat about natural spaces, such as caves? The US military became very interested in the acoustics of caves and tunnels during the hunt for Osama Bin Laden in Afghanistan. The idea was to give troops a better understanding of the layout of subterranean passages before they entered. David Bowen, from the acoustic consultancy Acentech, investigated the feasibility by having soldiers fire a gun four or five times at the mouth of a cave and recording the acoustic result. The branches, constrictions, and caverns would alter the way the sound reverberates. This information would reflect back to microphones at the entrance, allowing the cave’s geometry to be inferred. 39
    Cave geometry can produce wonderful reverberations. Smoo Cave on the north coast of Scotland emerges among some of the most spectacular and rugged terrain in Britain, with stony green mountains and glorious sandy beaches being bombarded by crashing waves. Nine months after hearing the Hamilton Mausoleum, I went to visit the cave in the hope of finding a more reverberant place. I entered through a large, gaping arch in a sheer limestone cliff cut by the sea. But the first chamber was not as reverberant as I had hoped, because the entrance was very open and there was a large hole in the roof, so the sound quickly disappeared. The second chamber was much more interesting, with a waterfall crashing through a hole in the ceiling, falling 25 meters (about 80 feet) to the flooded