This is prompted in part by the near-war going on in another forum about the Furutech demag.
Audio writers, especially those of the objective data type, talk about 20hz-20khz being the limits of human hearing, excepting the occasional young person (when I was 16, I could clearly hear out to 22khz without more than about a 3db drop).
It happens I'm reading Helmholtz's classic 19th century work "On the Sensations of Tone," and his experiments show human hearing out to at least *40khz* with no substantial db drop. (Helmholtz's translator Ellis reports being able to hear 40,000hz from a tone generator at a distance of 100 feet-- this is on p. 18 of the Dover edition) Helmholtz's terminology is exactly the same (he of course refers to cycles per second rather than Hertz, but considers A to be between 435 and 440cps), and the experiments look pretty much the same as the ones I did in 11th grade physics lab 20 years ago. Except for the results.
So here's the question-- is there a problem with Helmholtz's saws and bows (or academic honesty?) that I'm missing, or has human hearing gotten substantially worse since the Industrial Revolution?