The Sound Book

In a paper in Nature he wrote, “In the deep caves of Font-de-Gaume and Lascaux, the images of horses, bulls, bison and deer are found in regions with high levels of sound reflection, whereas feline art is found in regions of the caves with poor acoustics.”36 It seems that our ancient ancestors were exploiting cave acoustics as they told stories around their drawings, with tales of loud hoofed animals being amplified by reflections, whereas quiet cats called for no sonic reinforcement.

Even today, acoustic engineers carry out measurements using “white” and “pink” noise. When paints are mixed together they form a particular color because the various pigments alter the frequency balance of the reflected light. Blue paint reflects light of a higher frequency than red paint. Similarly, acoustic engineers use colors to describe the dominant frequencies in sounds. White noise contains all frequencies in equal quantities and hisses rather like a poorly tuned radio. Pink noise contains more low frequencies, so it rumbles with a more thunderous quality.

For the third gunshot, I took off my headphones to appreciate the sound. The familiar crack of the gun was followed by a wave of explosion that washed past me and bounced off the end wall, before returning and bathing me in reverberance from all directions. If the world ends with an apocalyptic thunder crack, this is what it will sound like, with the rumble lingering and forlornly dying away. I wanted to shout with astonishment, but I had to remain silent so as not to ruin the recording.

But measuring such a reverberant space was not straightforward. If either I or Allan made a noise—for example, saying to the other something like, “OK, ready to measure”—we would have to wait a minute or more for the sound to die away before we could fire the gun. We also had to stand completely still and make no noise while the sound was decaying, because otherwise the measurement would be ruined. Since we were standing about a hundred yards apart in the pitch black, hand signals were out of the question. Allan suggested we signal by shining torches on the ceiling.

Stuart Dempster commented, “Usually when you stop for a mistake, the mistake has the decency to stop too, but it doesn’t [in the cistern;] it just sits there and laughs at you . . . You have to be a clever composer [or improviser] and incorporate all your errors into the piece.”53

The midfrequencies are where speech is the most powerful, where our ears are the most sensitive, and hence where reverberation times are the most important for clear hearing.

He was monitoring for faults in the system that might cause the sound circling between the microphones and loudspeakers to grow louder and louder, resulting in feedback, the howling and screeching we associate with heavy metal.

In the ceiling of the hall, microphones were mounted inside pots to pick up sound at particular frequencies. The electronic signals from the microphones were then amplified and fed to loudspeakers elsewhere in the ceiling. The sound circulated around a loop, going from microphone to loudspeaker through the electronics, and then from loudspeaker to microphone through the air. This setup sustained the sound for longer in the hall, creating artificial reverberation.

These reflections also make the orchestra appear physically wider than it is—an effect called source broadening, which listeners tend to like

However, the most important frequencies are not at the extremes of hearing. A grand piano has notes from only about 30 to 4,000 hertz. Outside that range we cannot easily discern pitch, and all notes start to sound the same. Beyond 4,000 hertz, melodies are turned into the mindless whistling of someone who is tone-deaf