A SHIVER of anticipation swept through the audience as they took their seats in Liverpool’s Metropolitan Cathedral one evening last September. For this was to be a recital with a difference.
The soloist was a young Russian pianist with an impressive reputation for interpreting 20th-century classical music. But this time she had some unusual accompanists: two scientists from the National Physical Laboratory (NPL) near London. And they were playing a 5-metre long sewer pipe.
The pipe was part of an “infrasound generator” developed by the NPL scientists specially for the concert. It was designed to produce a frequency of 17.5 hertz, which is just below the lower threshold for audibility of 20 hertz, putting it in the range of frequencies known as infrasound. So although the pipe should have been inaudible, the aim was to see whether the audience would somehow be able to sense when it was playing. Would it affect their appreciation of the music?
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The Liverpool recital – billed as soundless music – was the dress rehearsal in an ambitious experiment designed to answer these questions. The experiment, which will reach its climax next year, is the brainchild of Sarah Angliss, a composer and electroacoustics engineer, and the young pianist, who goes by the stage name of GéNIA.
Angliss was intrigued by the number of organs built over the past 300 years with pipes that pump out bass notes below 20 hertz. The world’s largest organ, in the Convention Hall in Atlantic City, New Jersey, is an impressive sight with 33,000 pipes, the largest of which is 19.7 metres long. The fundamental frequency of this pipe is less than 9 hertz – more than 20 semitones below the lowest note on a piano keyboard. The only other organ with a pipe that length is in the town hall in Sydney. But lots of other organs have 9.75-metre pipes with fundamental frequencies in the infrasound range. So what, Angliss wondered, is the point of these pipes?
Angliss had hoped that organ builders themselves would have some answers, but she was disappointed. “Their views are completely polarised,” she says. “Some say they’re the most profound things. Others say they’re a waste of time and money.” Those who say the pipes do have a point argue that although people may not hear the sound, they can sense it at some subliminal level. Angliss compares it to looking at a black object in a very dark room: you know it is there even though you can’t see it properly.
Infrasound enthusiasts also believe that the low notes help to create a sense of awe in a cathedral. And they might be right. Intense infrasound is known to make some people hyperventilate, while others feel breathless or oppressed. And in one strange case, reports of a ghostly presence in a laboratory were traced to infrasound generated by an extractor fan (see New Scientist, 19 December 1998, p 42). The only way Angliss was going to know for sure if infrasound could affect people’s appreciation of music was to design a controlled experiment. But infrasound is uncharted territory for scientists and artists alike.
For a start, says Richard Lord of the NPL, infrasound isn’t always strictly inaudible. “You can hear it,” he says. “It just needs to be loud enough.” How audible it is depends on the person, as well as their age and sex. As a rule of thumb, you can hear a note of 19 hertz if it’s played louder than 86 decibels – at higher frequencies that’s the sort of noise generated by a loud vacuum cleaner or an electric drill. However, the researchers had to keep their eye on the volume: infrasound played at 120 decibels can induce temporary deafness.
For the concert in Liverpool, Lord and his colleagues used an infrasound generator made from a 5-metre length of heavy-duty plastic pipe about 40 centimetres in diameter. They produced the note in the tube using a high-quality bass speaker placed about a third of the way along the pipe. The generator was suspended to prevent the audience sensing any ground-borne vibrations.
The NPL team tucked themselves away in an alcove with the generator, hidden from the audience and GéNIA, so that no one would know exactly when the infrasound was played. When a light came on in front of the audience at points during the concert, the listeners were asked to write down their answers to a questionnaire. On hand to monitor the audience’s response was Ciaran O’Keeffe, a psychologist from the University of Hertfordshire.
When the NPL scientists monitored the infrasound in the cathedral, they discovered the room’s acoustics had an unexpected effect on the distribution of sound.
The cathedral is a circular building with a domed roof. For the recital, the piano was placed in the centre of the building, with the audience seated in rows surrounding it, while the alcove containing the pipe was some 20 metres away from the piano.
It turned out that the building focused the infrasound waves, producing a volume “hot spot” in the centre at GéNIA’s piano. Unfortunately the audience received the infrasound at lower volume. The researchers also had to cope with an unexpected source of infrasound – a passing truck that produced almost exactly the same frequency as the generator. But they weren’t too bothered. “From the start this was only going to be a pilot study to sort out the logistics,” says O’Keeffe, who has been analysing the results.
Unfortunately, Angliss reckoned that the infrasound wasn’t very noticeable. “I felt it was a damp squib,” she says. However, the team was far more impressed by the preliminary rehearsals they did in a London church. GéNIA agrees, saying that she was definitely aware of the infrasound in London: “It was the most amazing experience doing the rehearsal.” This could be partly due to the psychological effect of having the infrasound generator next to the piano during the trial run. Then again, rehearsals are not the same as a public performance. “When you are performing, you’re too immersed to notice what is going on around you,” GéNIA points out.
But despite the team’s disappointment, the audience in Liverpool did seem to respond to the infrasound. People were noting down comments like “a tingly feeling in the back of my neck”, “something in my stomach” and “a sense of presence” when the infrasound was on. “We’re treating the results so far with caution,” says O’Keeffe.
He and his colleagues will get their big chance to test the effects of infrasound next year. The Liverpool recital was only the dress rehearsal for two concerts to be held in London’s Purcell Room next May. Although the programme has yet to be finalised, it will include pieces by composers such as Claude Debussy and Philip Glass, as well as two specially commissioned works, including one by Angliss.
And it’s not just the music that will be special. For their big London debut next year, the NPL scientists are designing three more infrasound generators to improve the coverage of the audience, and they plan to turn up the volume to achieve a better effect. “We’ll still be well within safety limits,” says Lord.
Orchestras have a long history of adopting unusual musical instruments. Tchaikovsky’s 1812 Overture requires a cannon for the retreat of Napoleon from Moscow, while Edgard Varèse wrote for anvil and siren. If it turns out that infrasound does enhance our emotional response to music, how long will it be before orchestras find a place for the B-flat drain pipe?
- Soundless Music will be played at the Purcell Room in London on 31 May 2003