Ralph West's November obituary prompted a letter of appreciation from a reader who added a query regarding the Voigt quarter-wave loudspeaker principle embraced by Ralph. How was it, he asked, that the drive-unit's position a third of the way from the closed end has a deterrent effect on the system's 3rd-harmonic, as it seemed to him that this location would be more likely to activate it. I promptly sent off a final page-proof of last month's 'opinion' piece, directing his attention to its discussion of nodes and antinodes in relation to standing-waves, which I thought should settle the matter. But it didn't, and as the same point has been brought up by others over the years, I'll try to throw a little more light on it. More, that is, than I'd managed to shed in that January attempt to explain the locations of sonic excitation-points in caves.
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