text: BBC Radio 4 - Material World, Acoustic Mapping - The Earth's Big Dynamo
  Acoustic Mapping - The Earth's Big Dynamo
  Scientists have been recreating the exact sounds of a building without having to actually be there.
  Sue Nelson talks to Damian Murphy from York University who is using the latest acoustic mapping techniques to recreate the exact sound of ancient and new buildings.
  He does this by capturing a series of room impulse response profiles - the acoustic fingerprint of a particular environment for a sound source and listener located at a specific position within it.
  He can even recreate the acoustics of buildings that no longer exist, such as the old cathedral in Coventry.
  Sue also talks to psychoacoustics expert Dr. Peter Rutherford from the School of the Built Environment at the University of Nottingham about how we hear and the interplay between music and the environment.
  He explains how the physical acoustic properties of a building can change depending on how your brain listens to it and why the designers of concert halls are increasingly turning to scientific techniques to create exactly the right kind of sound.
  The Earth's big dynamo
  The problem of how the Earth generates and maintains its magnetic field was described by Einstein as one of the top five problems facing physics.
  Theory has been about 30 years ahead of experiment in the realm of "Magnetohydrodynamics" – the area of physics that deals with how a massive ball of liquid metal can generate, and sustain, a magnetic field in the way the Earth's core seems to.
  Recently a team of scientists in France have taken the lead in the race to build a model Earth by stirring a tank of liquid sodium using a pair of propellers spinning in opposite directions.
  Joining Sue to discuss how such a simple apparatus has potentially opened up a whole new corner of experimental physics is Professor Keith Moffatt of Trinity College, Cambridge and Dr Jean-François Pinton of the Ecole Normale Supérieure in Lyon.