Infrasonic - the pipe
Infrasound generator, designed and built for this experiment
In order to generate enough infrasound to fill the Purcell Room, we had to build an infrasonic generator - ordinary speakers couldn't play it at the volumes we wanted to acheive. Our generator was an extra-long stroke subwoofer in a sewer pipe that was around 6 metres long. It was driven by a sine wave generator, amplified by a power amp that had a flat frequency response down to 10Hz.
For acousticians:
Tests at the National Physical Laboratory showed this was performing as a quarter-wavelength pipe. Tests showed the pipe had a resonant frequency of 17.4Hz.
We realised such a large pipe would be difficult to move from venue to venue so we employed Tim Hunkin (engineer, cartoonist and sculptor) and Graham Norgate to put it together, according to our designs, so it would be portable. Tim and Graham are both excellent craftsman - and Tim has the added advantage of a owning the biggest shed we've ever seen! (pictured above).
The pipe is very well together - Richard Lord (NPL) and I have been carting it around the country ever since. It recently made an appearance in my event at the Edinburgh International Science Festival and in my new, collaborative theatre piece Senster.
NB The strange, white figure standing in the back of these photos has nothing to do with the experiment! It's a mock crash-test dummy, made by Tim for The Human Factor, an exhibition that we put together for the Science Museum, UK, around 1997.
Equipment from the National Physical Laboratory is used to test the frequency response of the pipe
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