Speaker hum when I connect my external computer monitor
by Sean McPhillips
on
Aug 3, 2008 at 12:40:38 am
Hi,
I've just bought a pair of KRK Rokit 5 powered speakers to plug into my MacBook Pro (via the unbalanced audio/headphones out plug) for monitoring audio out of Final Cut Pro (for example).
They sound great until I plug my external computer monitor (Samsung Synchmaster 205BW) into the MBP - at which point I get a loud hum through both speakers.
According to the Rokit 5 manual any video monitors have to be on a different circuit than the speakers, so I went and got myself a couple of extension leads and proceeded to plug the Synchmaster into every power point I could find in our office (seven in total), and got the hum every time.
Now there are four power circuits in this office so unless all the points are coming off only one of them for some reason, that doesn't seem to be the problem.
Re: Speaker hum when I connect my external computer monitor by Sean ONeil on Aug 3, 2008 at 4:17:32 am
Computer speakers are horrible. They pick up any type of noise there is. Having a cellphone even near them is going to cause a really loud hum. You should return them.
Re: Speaker hum when I connect my external computer monitor by Chuck Reti on Aug 3, 2008 at 5:05:38 pm
[Sean ONeil]"Having a cellphone even near them is going to cause a really loud hum." (Sorry for inadvertent blank post above.)
The digital signal that the current generation of GSM/G3 phones generate gets into almost everything, not just nearby speakers.
On both studio and EFP shoots, we have to make sure crew and talent cell phones are in the full Power OFF, not just 'silent/ring off' mode to avoid the buzz getting into both wired and wireless mikes. Same with studio headsets and intercoms. Have heard this even on radio programs when talent's phone gets into the audio board. This will occur all by itself, when the cell phone and nearby tower sites need to communicate with each other, not just when a call is in progress.
As to the OP's hum problem, it does sound like a ground issue, which can affect audio monitoring regardless of the equipment price or manufacturer. Besides the recommendation to try an isolation transformer (though i suspect everything's on wall warts anyway), sometimes careful re-dressing of power and audio cables can help. Make sure speakers and speaker leads are nowhere near power supply or mains cables and especially transformers.
My next question is, if that fixes the problem, do I still have to worry that there is a ground loop problem in the building? Is it inherently dangerous or just a fact of life?
I understand that a power conditioning unit would be another possible fix and probably a good idea generally but to solve this problem, at AU$60 v AU$500+ I'd rather go with the cheap option at this stage.
Other than that,, well,, you are plugging into the KRK's unbalanced,, Make sure the wire going from your computer to the speaker isn't running along side any AC cables, power adapters, so on... If you have to pass over an AC cable, do so at a 180Deg angle.
Also, try to use a decent cable. If you're using a thin radioshack'ish mini-plug to RCA cable with thin to no shielding, you will pick up all sorts of ugly frequencies.
Re: Speaker hum when I connect my external computer monitor by david bogie on Aug 4, 2008 at 3:00:01 pm
q[Sean McPhillips]"I'll post here again once I've had a go at it. "
And please go back to all of the other forums where you have posted this same question.
You've gotten a weird range of mutually exclusive advice and suggestions on how to handle interference caused by many different sources. We would like to know what worked and what diddn't.
bogiesan
This is my standard sigfile so do not take it personally: "For crying out loud, read the freakin' manual."
