The method I am using as I have said before is a small mass mounted on the end of a flat spring and tuned to a frequency of 48 cycles per second. To avoid any possible contamination with the mains, the vibrating mass is a piece of thin glass 5 mm square on which has been drawn 10 lines, A similar piece of glass is mounted in a fixed frame and a laser beam shines through them. The fixed glass is rotated to produce a Moire fringe pattern and the movement of fringe detected with a photo cell. The resulting voltage is amplified and rectified using an opamp precision half wave rectifier. The rectified voltage is passed through a low pass filter to extract the modulation voltage the amplitude of which is a measure of the Hum intensity. All electrical power must be supplied by battery and if possible the mains supply to the building turned off.
On Sep 11, 10:26 am, Trev <[email protected]> wrote: > Yes, I appreciate that John. It's just a bit confusing if you post a > disconnected sound to an analysis. > I have never heard anyone describe or post such a sound with high sibilants > in it. > The 'drone' is what gets to most people -and it is boring in the extreme. > What would be nice is a audio modulated optical signal from your gravity > mass vibrating device and see if that fits the bill. I know you say it > can't be done but I wouldn't mind having a go after some design work. > > > > On Monday, 10 September 2012 20:10:46 UTC+1, John Dawes wrote: > > > I made it clear that this was not a sound recording of the Hum. It has > > been known for many years that not everybody hears the same sound and > > there is no reason why they should. The perception of noise is > > generated inside the body and will depend upon the individual. Some > > perceive it as a low rumble others at a much higher frequency. Some > > hear it as a continuous note and some as a pulse which they describe > > as Morse Code . The purpose of this exercise is measurement, for > > without measurement you have nothing, what it sounds like is > > irrelevant. > > > On Sep 10, 6:37 pm, Trev <[email protected]> wrote: > > > John, thet sample sounds very like a raspy mains hum- not even remotely > > > like my hum- for the record :) > > > Also, I notice some corona discharge noise in there too. Was this > > recorded > > > at/near a local HV substation? > > > > - Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > - Show quoted text - -- You received this message because you are subscribed to the Google Groups "Hum Sufferers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/hum-sufferers?hl=en.
