A Semiconductor work by Ruth Jarman and Joe Gerhardt. 20 Hz observes a geo-magnetic storm occurring in the Earth's upper atmosphere. Working with data collected from the CARISMA radio array and interpreted as audio, we hear tweeting and rumbles caused by incoming solar wind, captured at the frequency of 20 Hertz. Generated directly by the sound, tangible and sculptural forms emerge suggestive of scientific visualisations. As different frequencies interact both visually and aurally, complex patterns emerge to create interference phenomena that probe the limits of our perception.