Plasma Speaker

I was super excited to get to show my prototypes on the floor of the exploratorium last Friday. The main exhibit I worked on and brought in was my 'Plasma Speaker' prototype. I also showed the platform with lasers and acrylic shapes, which I titled 'Laser Island'.

For the plasma speaker, I didn't quite get the physical unit built up to the level that I would have liked beforehand, and as a result I had to sit next to the exhibit the whole time to make sure people didn't shock themselves. All of the high voltage connections were insulated, but there were still loose wires showing and the terminals of the 12V batteries were exposed, so my presence was required and my attention had to be focused primarily on any possible dangers rather than the interaction. I would have liked to back off a bit and just observe how people approach and interact with the piece, but being right there to answer questions and hear any initial comments was nice too.

Since we showed on one day, we had to split up into pre and post lunch showings. The morning was filled with field trip groups of mostly school children with some adult supervision. The afternoon was much more relaxed in general and consisted of smaller groups and families with younger children.

The bigger rush in the morning meant that there was a constant flow of mostly children next to the plasma speaker. The kids were great! They were interested, engaged, and asked questions about how the arc worked and how it made sound. This gave me a great opportunity to explain things in simple terms compared to the more technical details I tend to get into when speaking with Stanford engineering students. In the few moments when one of the adults came over without the kids, I was able to practice my explanation of the effect to them also and judge by their reaction how technical I should be.

My electronics were not sounding very clean, and a static noise started showing up and covering most of the music playing through the speaker. I thought this would be a bad thing, but there were some pleasant unexpected results. For example, when the arc gap was increased beyond a distance that the arc could sustain itself, there was a really interesting lightning effect. This doesn't happen when there is no sound, and the static noise made the effect much more pronounced than with any music source I've tried so far.

In the final piece, I may not want to allow the gap to increase to a size that allows this. I think it is an interesting state of the arc, but it may be a distraction from the regular mode of the singing plasma arc.

In the afternoon, the smaller group and family dynamic changed how people approached and interacted. The initial approach was usually made by a parent, and then they would call attention to the children. Sometimes this worked, and sometimes the kids were just distracted by the giant mirror exhibit within view.

After having the chance to reflect on the day, I've thought of a number of changes to make for the next version.

In the electronics, I tried to build a second circuit on the breadboard and I think there was interference either from that or from spikes in the power supply rails coupling with oscillations in the input stage, causing some feedback that caused the static noise. I also was having issues with controlling my phone anytime I plugged it in, so I'm going to add an input amplifier/buffer circuit to isolate the sound source from any high voltage or high frequency feedback.

The arc was much weaker at the end of the day compared to the beginning, which tells me that my batteries aren't lasting as long as I'd like. I'm ordering a 36V power supply to try to replace the batteries with something more consistent over time.

For safety issues, I need to build a box that more fully encloses the electronics and the power supply. I may also need to alter the geometry of the cover because there is a lot of heat coming out of the top all directed towards an area that is easily within arms reach.

I don't think anyone had any problem believing that the sound was coming from the arc, so the transparency of the device was pretty good. I'll just have to make sure I don't make it worse when building up the enclosure.

For the handle, I'd like to build in some adjustable hard stops so I can control the range of the moving electrode and keep it within a distance that doesn't get too far away from the optimal sustainable arc range. If the limit does extend out into the 'lightning zone', I'll attempt to add some springs to bias it back after the handle is released.