The Rise and Fall of the Lesser Load-Dependent Adaptive Power Bicore-Controlled Electromagnetic String Driver.
La Monte Young would certainly have come up with a different name, but he might just as much have sat back and lit up for this one. Such is minimalism.
It started as a robot. Actually not. It started as a starry-eyed vision of a minimal 8-node circuit that remembers so well that it would repeat phrases spoken at it. 8 timed circuits strung in a loop, high-impedance loudspeakers acting as both inputs and outputs, with trimmers to ground and DIP switches as output mixers. I actually built it; on a neat PCB I designed before testing. It was bound to work. Of course I switched it on with bated breath, timidly whispering “hallo” into one of the speakers. It did exactly nothing – no pop, no phlogiston escaping, no hum, no hiss, no furtive words darkly spoken: “daddy, is that you?” Not once. At least it’s predictable I thought, thinking of politicians in Africa. It has turned out remarkably more predictable than that.
That’s where the robot first came in: I showed it to my friend Willem.
“Ah, a BEAM circuit.”
“BEAM?” He typed the word into Google.
“It’s an octo-core.”
“Well, it isn’t working,” I said defensively.
You get the idea.
Then Willem’s dad wanted to make an art work with BEAM robots crawling over some letters. We were called in and a quantity of money was put on the table. Willem immediately went to buy smokes and I started struggling with a few components on a lit from below glass table. By the time I started needing an own pair of glasses, the thirty or so components had become five. And it was still working. The euphoria evaporated as soon as we tried it on a solar cell: it needed more voltage, and a little more current. Miller engines simply didn’t. Around the time I reduced a second 555 (and Willem his 400th cigarette) to holy smoke, his dad returned and I was fired. “Mark Tilden,” they said. I moved to Cape Town.
Time to get serious – I called up Brendon Bussy. Brendon builds small stringed instruments from fish cans and dowel sticks and plays on them. He also plays the mandolin rather well, sometimes through Audiomulch and sometimes not. One day he wants to teach informal settlement urchins to do the same things.
By now I had Wednesdays in the bag. Brendon would pick me up at the Waterfront and we’d tinker ’till it was time to go home. The circuit had decided to remain being a bicore – we dropped one component (why five if you can have four?) strung a loudspeaker in circuit and powered up. It buzzed like hell. We swapped components – it still buzzed, exactly like the hell it was buzzing like before. Interesting, we thought (although by now we’d started using words like “interezzting”.) There was one (not totally unexpected) phenomenon: whenever one pushed on the loudspeaker cone, the sound changed markedly. One could shift the pitch by about an octave without damaging the cone. This made sense – the loudspeaker impedance forms the resistive element of the RC timing circuit. Pushing on the cone changes the Thiele-Small parameters of the loudspeaker and moves around the resonance peak of its impedance curve. The circuit reacted to this, by oscillating faster or slower, depending on which “side” of the impedance peak it was operating. This is not what every monostable circuit does. In addition the generated wave forms were quite complex. It had become moot whether this was because of “learning behaviour” (loop hysteresis) or because of complex interactions with the load due to impedance changes and reverse EMF. But the buzzing was monotonous and pitched right in a nasty region of one’s hearing, exactly there where Fletcher-Munson indicates the greatest sensitivity. A suitable resonator improved matters slightly, but it remained daunting to listen for more than a few seconds.
By this time it had become clear that we either needed oodles more variation, a different register or a different and more chaotic resonator than a loudspeaker cone. A fortnight before, Brendon had stretched a string across a lagoon at Kogelbaai to create a wind harp. This worked beautifully, producing a whole wreath of haunting drone-like sounds. If the practically linear movement of air over a simple string could produce such harmonics, the circuit-without-name would probably do at least as well. The next week we glued a tube onto a small loudspeaker driver and tried connecting it to a nylon string Brendon had strung across his work bench. Predictably it buzzed like hell. Sounds coming from a piezoelectric transducer stuck to a small fish can resonator (Glenryck, I think) were more interesting, but there still was a lot of “bleed” of the unmitigated loudspeaker buzz, even on the piezo output. We started winding solenoids, to create a drive which produces very little sound of it’s own. These didn’t work, no surprises, with too thick a wire gauge and too few windings. Brendon mentioned a door bell..
The next week I was greeted by a weird one-stringed instrument on Brendon’s bench, with the bridge and resonator (KOO Pilchards in Chilli Sauce) equidistant from the two ends. The string was steel.. We quickly removed from its cradle, re-wired and re-mounted the solenoid on a piece of wood, flanked it with a mild steel magnetic cradle with two cut-outs where the string could pass through and tried it on the naked string. It started buzzing, softly, but happily. A great relief. Brendon recorded a few minutes. Levels weren’t optimal. Perhaps another resonator. His old mandolin had a suitable steel bass string and didn’t object to being recorded. Exactly this, on a CD he hastily made me as I was leaving, is what I’ve been listening to for the last five days. We’re not even close to the end yet, I’m sure, but I think it’s time to start choosing a name for the circuit. And it won’t be Tilden.