Viaduct echoes

In the village where I grew up is a viaduct which is great for shouting into, as you get good echoes. My mum and I still shout into it when we walk under it. She suggested that it should speak back to you when you shout into it, so I've connected up the Bare Conductive Touch Board to a sound detector. When the sound level is high enough, an MP3 will be played. Currently it plays back me saying "echo".

I can't visit the viaduct at the moment, but for now, I am shouting at a picture of the viaduct and it is shouting back.

Video on Flickr: Viaduct echo.