How we built the Fire Organ
August 17, 2015 by louis
This guest blog post is from Matthew Duckett, a Guerilla Science collaborator and structural engineer with Buro Happold. Matt and his colleagues worked with us to build the Fire Organ, a flaming tower of awesomeness that’s touring the UK throughout summer and autumn 2015.
My first experience of a Rubens’ tube was watching MythBusters as a kid. Adam Savage lit the flame – “a stunning visual representation of a soundwave” – and I couldn’t fail to be mesmerised. I realised that sound wasn’t only something that could be heard – it was visible and tangible too. With this childhood fascination in mind it was no surprise that I jumped at the opportunity when Guerilla Science asked if I would help to design and build a five-headed version of a Rubens’ tube (aka the Fire Organ) and then take it around the country on a tour of festivals and schools.
I’ve been working on the project with a number of colleagues from Buro Happold, a company who thrive from using engineering as a visual and emotional stimulus. My day job is as a structural engineer, which came in handy with design of the organ, but we also had acoustic, fire and bridge engineers on board as part of the team. Looking at the Fire Organ, I see a spectacular manifestation of scientific and engineering principles – and it’s important for us to get this across to audiences at the festivals where we’re showcasing the organ. However, being the only five-piped Rubens’ tube this side of the Atlantic (and one of the biggest in the world!) we also wanted the Fire Organ to be more than a teaching prop and to really wow people and connect with them on an emotional level.
To enhance the performance we wanted to optimise certain features of the Fire Organ to make it highly visual and interactive, and allow audience members to play it themselves and directly witness the effects of the sounds they were producing. The speakers are therefore set up to allow an audience member to plug in anything they want that could produce a sound – microphones, guitars, iPods, keyboards, laptops – and get a real time visualisation of the sound… in fire!
During our performances we’ve been explaining some of the concepts behind the Fire Organ, so I’m going to try and get a few of the basics down here.
Essentially the Rubens’ tube works by attaching a speaker behind a rubber membrane at one end of the tube, with a solid cap at the other. Sound is a vibration of air, so the sound from the speaker vibrates the flexible rubber membrane, which causes compressions in the air which travel down the tube, known as sound waves. These reflect off of the solid end of the pipe and travel back – like in the digram below.
If the waves are at the right frequency, the waves travel back on each other in the same phase. This causes them to superimpose (add together) or cancel out and form what is known as a “standing wave”.
The standing wave forms areas of higher and lower pressures, which causes the gas particles to bunch up or dissipate. Where the pressure is low, shorter flames are produced and where the pressure is high, taller flames shoot out of the Fire Organ.
The Fire Organ project is generously supported by the Royal Academy of Engineering.