Originally Posted by Fatawan
There is also the possibility the cable guys never properly grounded it outside the house. My house and cable use the same ground rod outside and I have never had any hum. Go outside and check that its properly grounded before spending money. Treat the disease, not the symptoms(if possible, of course)
truth be told..
if you ground the AC system and the cable system to the same rod, it doesnt mean the problem goes away.. it means the problem is simply much smaller, to the point of not being noticeable through hum from a speaker.. but still possible to be seen with the measuring equipment.
the reason for that is because the ground signal has two sources of entry.. one from the AC system and one from the cable system.
one would think, if the electrical grid was really networked, then those two systems would use the same exact ground .. and if that were true, then there wouldnt be any ground hum at all to be heard.
and be smart.. every cable connection, as well as every AC system connection all have (or are typically supposed to have) an individual ground connection per house.
and that doesnt say anything about the cable system having any ground connections at the hub boxes that sit outside in the neighborhood.
it is easier to simpy assume there are two individual ground sources using two seperate grids, and those two have come into contact with eachother and the connection must be broken.
what that little filter does is break the connection.
i've got the same problem here, and it got a whole lot worse when i connected the television to the computer .. there was a rolling hum bar on the screen and noise from the speaker.
and comcast didnt care to do anything about it, probably because i disconnected the computer from the television and the hum bar went away.
i told them to listen to the headphones to hear the hum, and they acknowledge it was there.. but they said they wouldnt do anything about fixing it, leaving it up to me to get one of them isolator filters.
truth be told..
it is simply because the cable box doesnt have the filter already installed inside on the circuit board as it should, leaving room for people to go out and get one themselves.
and yes, it is possible to ground both systems to the same rod.. but most houses dont even use a ground rod into the house, they mount a strap to the metal pipe that holds the high voltage electrical wires.
with that said.. most houses need a cable box with the filter inside of it, but it does save money to build the box without the isolator on the circuit.
and more to the point ... if the box already had an isolator inside of it, and the customer put another isolator on the line.. it could actually age the cable hub outside somewhat faster, or cause line distortion that plagues the signal.
and i think hackers would want to use two isolators to try and slow the signal down (or at least put a gap of space in the line) to grab information and inject their data into the line.. known as a sandbox.
if 60hz is what the ground is functioning at .. then the isolator is basically just a transformer that allows all frequencies to pass through the air from the copper to the magnet except for 60hz.
kinda like a parametric equalizer with a very narrow Q (down to one frequency only)
but it is better to view it as electrons flowing from the copper to the magnet.
they say it is just a capacitor.. and that means the capacitor has been engineering using chemistry to specifically block one single frequency and let everything else pass.
the real problem is adding two of those capacitors together.. because 61hz starts to bend in, and 62hz starts to bend in.. and in terms of tiny distortion, those two frequencies bowing in starts to fill up the 60hz area again .. that is known to the world as harmonics.
and if you want to read up about it.. you could take the kindergarden route and view maxxbass bass enhancer, because they claim to give speakers more bass by adding two frequencies together to make it sound like lower bass.
and the principle really works extremely well.
the one frequency gets thrown out from the speaker, and the second frequency is a subtraction at a specific rate .. and the rate is what changes the physical
soundwave to become the lower bass frequency.
(just saying.. on a forum like this.. that is how you get 20hz from a ported subwoofer box tuned to 32hz)
it works as long as the room isnt a pressure chamber.
(and if there is mild pressure in the room, that simply means the sound processor needs to be adjusted to bring the functionality back up)
be sure to share that information before the moderators come in here claiming i am off topic with my audio advice on an audio|video forum.