I gasped. An almost perfect 300Hz squarewave had appeared on the oscilloscope screen—something I had never before seen from a loudspeaker.

It was the spring of 1982. John Crabbe, then editor of the British magazine Hi-Fi News & Record Review, and I had driven up to Quad's factory in Huntingdon, England. The ESL-63 electrostatic loudspeaker had been launched the previous summer, and we were to interview its designer, Peter J. Walker, for an article that would appear in the July 1982 issue of HFN/RR. Peter set up a pair of ESL-63s on wooden kitchen chairs, fed one of them a 300Hz squarewave, casually placed a mike before it, and showed us the result on the 'scope. "Of course, why should a speaker being able to reproduce a squarewave matter at all, hmmm?" he rhetorically asked us.