Hot-wired piano tunes itself
NewScientist.com 19:00 04 December 02 Mick Hamer A piano that tunes itself is due to go on sale at the end of 2003. All the pianist has to do is hit a switch and wait for 40 seconds while hidden electronics tune the strings. With more than 200 strings inside them, pianos are the one musical instrument that musicians cannot normally tune themselves. And even after tuning by a professional, strings quickly go out of tune because of slight changes in temperature, humidity and the permanent stretching of the piano wire under tension. The idea of a self-tuning piano is not new but, until now, most inventors have tried to develop devices that mechanically alter the string tension in the same way that a human piano tuner would do. In a piano, one end of each string is wrapped around a metal pin. The human tuner adjusts the tension by turning the pins, increasing the tension to raise a flat note, and reducing it if the string's note is too sharp. No moving parts Don Gilmore, an inventor based in Kansas City, Missouri, has come up with an electronic self-tuning piano with no inherently unreliable moving parts. Gilmore had good reason to find a better way to keep pianos in tune. He trained as a classical pianist in the 1970s before he became a mechanical engineer and inventor. "My piano at home is audibly out of tune a fortnight after being tuned," he says. During a three-month break between jobs, Gilmore firmed up his idea for a self-tuning piano. He realised that carefully controlled electric currents could be used to tune the strings - based on the principle that warming a string with an electric current causes it to expand, reducing its tension. Before it leaves the factory, Gilmore's invention requires a piano's strings to be manually tuned nearly a third of a semitone sharp. The system then tunes the piano using a warming current to ease the tension of the strings. Underneath each of the strings are two magnetic coils, like those used in electric guitar pickups. In a guitar, a vibrating metal string induces alternating current in the coil, producing the note. Gilmore uses the reverse effect: he applies a current to one coil, inducing a magnetic force that vibrates the string. This induces a small electrical current in the second coil, which is amplified and fed into a frequency analyser. "Absolutely appalling" A microcomputer compares this frequency with the correct frequency for each string and then instructs a power transistor to deliver pulses of a correcting current through the string. The pulses warm the string, lowering the pitch to the correct frequency. The sound from each string during the tuning process is scarcely audible, says Gilmore. The electronically controlled strings have an operating temperature of around 35�C. "The strings feel as though somebody has just put their hand on them," says Gilmore. The piano draws about 500 to 600 watts. Gilmore's system will go on sale in some grand pianos made by American piano maker Story and Clark at the end of 2003. But the firm says it is too early to say exactly how much extra a self-tuning piano will cost. As might be expected, piano tuners are unimpressed. "From a pragmatic point of view I think it's an absolutely appalling idea. It would put me out of a job," says Martin Surrey, who tunes pianos for the English National Opera company. He points out that one problem with the idea is that concert pianos have to be tuned to suit the acoustics of the room: "They can't be tuned to a fixed formula." 19:00 04 December 02
