Getting a Buzz - Useful Tip?

[ChrisHunt]

For those plagued by an annoying buzz from their sub (not at all nautical)...

I have one of these home cinema setups with an amp, speakers, sub, PVR etc and started getting a horrible buzzing in the sub. After much reading on the audio forums it seemed that the most likely cause was an earth loop feedback from two devices completing over the same earth. All sorts of potential resolutions, some Heath-Robinsonish and others downright dangerous and often expensive were suggested. Anyways after thinking b*gger me this is going to be tricky to solve I set about reading a bit more and frankly there was so much conflicting advice I was close to giving up. I'm delighted to say that the buzz is now Buzz Yesteryear and has disappeared from my system. For me the solution was fairly simple - I replaced the rather crappy cable I got with the sub for a Y cable with much better shielding (an improvement but not a cure) and remembering one of the key principles of induction I rearranged the power supply for the sub so that the power cable ran in a different direction to the audio cable with the result that the buzz has completely disappeared.

So there you go - a useful tip, possibly!

Regards,
Chris

[Airspeed]

Thank you Sir,
I'll remember that when I bolt the woofer to my Hurricane frame.

[Tako_Kichi]

I was a recording studio engineer when I lived in the UK and fighting hum on audio cables was an almost daily challenge. Running speaker cables alongside AC power cables is a sure-fire way of inducing hum into the audio system. They should be kept as far apart as possible and if they have to cross each other for some reason then the crossing should be made at 90 degrees to minimize interference.

Cheap cables, as you found out, are very prone to the problem too due to the nature of the cable. Normal speaker cables are un-shielded twin lead which means they are very susceptible to interference as they have no braid to keep out unwanted signals. The more copper in the core the better they are at rejecting unwanted interference. In addition the shorter the cable the better it as long cables act like antennas pulling unwanted signals into the system. I once had an issue at the studio where I suddenly started picking up radio signals whenever the fire station across the street used their radios. It took me days to track down the problem as it only happened when the studio was in use and the fire station were actually transmitting radio signals. The culprit turned out to be a bad XLR microphone cable with a broken ground connection but as there were over 20 mic cables hanging on the wall and different cables were in use each day (students would just grab cables at random so some days the bad cable was not in use) it took a while to find the bad one!

In really bad cases of interference you have to resort to using ferrite rings or ferrite beads on the audio cable in order to block the spurious signals. If you look at the monitor cables on your computer you will see ferrite rings at either end, they are the things that look like short plastic cylinders around the cable, and they are there to stop external signals interfering with the data being carried up the cable.

[Vancouver]

Good post, now can you solve an annoying noisy fridge motor for me, its a 5 year old Maytag so the warranty is up and drives me nuts.

[Dev One]

These things cause problems in aircraft installations too. I remember one experimental installation that put a 800Hz tone onto the radio & the local ATC were not very happy!! Tried Pi ferrite thimbles & screened cables without success, but one of the electricians remembered the routing of the cables & subtly changed its position & hey presto, noise gone.
Seems the unit had an AC motor with its own inverter that did not show up as having excessive radiation when tested in a special chamber, but this cable was alongside one of the power cables to the Radio in the aircraft!!
Happy serendipity days....
Keith