Re:Bose Hearphones
by Benofiniquity on Friday December 09, 2016 @03:16PM
(#13141462)
The hum you hear is actually double the mains frequency (100/120 Hz) with emphasis on odd harmonics going up. Magnetostriction gives you two expansion/contraction events per wavelength, effectively doubling the frequency. (If everything is perfect, spherical cow in a vacuum, &c.)
Re:Bose Hearphones
by twothamendment on Friday December 09, 2016 @03:12PM
(#13141437)
Yes, the one that came with my Amazon Echo is the worst. I can hear it from 15 feet away. If I walk up to it and push on it it stops. I don't think pushing on it really makes the difference, I was guessing that it has to do with grounding it or something electrical changes when I touch it.
https://en.wikipedia.org/wiki/Switched-mode_power_supply
"The operating frequency of an unloaded SMPS is sometimes in the audible human range, and may sound subjectively quite loud for people whose hearing is very sensitive to the relevant frequency range."
Even analog power supplies will generate a 50/60hz hum (depending on what the power-lines are providing)