This afternoon I experimented with making the propagation of a sine wave visible using a shallow amount of water in a cooking tray and a directional light source to capture the wave's movement. As with the bowl piece, I've been using my Marshall amplifier to drive the sine wave, the amp and speaker have been removed from the speaker box as this makes things more convenient. The thing about a cooking tray is that it (at a specific set of frequencies) it resonates quite violently, so not a great deal of volume is required for this phenomena to take effect. This is good as I really want the sine waves to be in the background as much as possible. Though they are part of acknowledging the intention behind this process (sound and vision), the sine waves shouldn't necessarily be the centre of attention, the beauty lies in its interaction with the metal tray, the water and the refracted light. I am thinking of incorporating this into an installation - a darkened space, with four or five of these trays (of various sizes), listeners would be given hand held torches and go around to each of the trays reflecting light off the moving surfaces of the water. The sine waves could also move in cents of frequency (gliss) as this would cause the waves to move and change shape and formation. I'll write more on this soon...
With the setup of speaker, water tray and directional light (amp and oscillator out of shot.) What I'm doing here is trying to move the waves around manually.
Example one: A low frequency resonance (note large bandwidth). The metal tray has many resonant nodes, the complicated formation is due to the waves reflecting off the edges and corners. It would be interesting to see a more pure representation of a single spherical formation - though this is proving difficult to acheive.
Example 2: A much more elaborate formation at a higher frequency with a shallower amount of water. A blue bulb was being used at the stage.