Subwoofer buzzes/hums when XBMC is open
#1
Hi,

I tried searching Google & these forums but couldn't find anything. Apologies if there is a common fix.

I have a problem when watching anything on xbmc (actually I can just be in the menus to hear it too) that makes my sub produce a humming/buzzing noise. It doesn't happen any other time unless xbmc is open. Although it does seem to be linked to the master PC volume ie if the volume is lower in app & raised on my amp then I hear it louder. As soon as I exit the app it immediately cuts off & I've never heard it on anything else.

All the other speakers sound fine & don't have the problem.

Any ideas anyone?

Thanks.
Reply
#2
Star 
Usually buzzing or humm.. is alternating signal slipping into the audio, a lot of older systems do it. This could be induced by the audio section of your PC or an external amplifier or harmonics in the cables. XBMC opens up the audio and you hear the noise.. close out XBMC and it closes the audio port no noise (no mystery here) The biggest offenders are cables inducing the humm (make sure the cables don't pass around AC cords) and bad grounds.

The easiest diagnosis is to try a different cable set, failing that; tie up the grounds (connect a single wire to the chassis of the PC and audio amp) or try another amplifier. Ensure that your connections are solid.. wiggle them with everything in place with the audio port open, you'll find the offender.. if it's a cable.

Just thought I'd mention something about the frequency of the buzz.... if it's an AC 60 cycle freq, it will sound like a neon sign, or ballast on a fluorescent tube on start up. If it doesn't have that ptich.. then the frequency is induced internally and the source is likely bad capacitors.
Reply
#3
Nuwidol Wrote:I have a problem when watching anything on xbmc (actually I can just be in the menus to hear it too) that makes my sub produce a humming/buzzing noise.
It more likely that the external amplifier in your subwoofer is fighting with AVR for possession of the ground. When there are devices want to define 0.00 volts, it generates hum. It's more likely that your subwoofer Amp plug is different from your AVR plug (2 prongs vs 3 prongs), one device is really using 0.001 volt and the other device uses something closer to 0.003 volts. The subwoofer RCA cable connects the two, and the fighting begins.

You have to find way to stop these two devices from trying to steal ground from each other, or get them to not "see" each other. First, make your system produce the humming noise and disconnect the subwoofer RCA cable between your receiver and subwoofer. If the humming noise stop, you have a ground loop issue.

The safest way to solve this problem is to buy a special subwoofer cable with little arrows on the wire to show the signal direction. Subwoofer RCA cable has two wires, and one being a shield. If you have the right tool (and if RCA cable is cheap enough to do this too), you can simply cut off the RCA cable shield wire at one end. The humming noise will more likely gone! Smile

Nuwidol Wrote:All the other speakers sound fine & don't have the problem.
Because all other speakers are powered by AVR amp.
>Alienware X51- do it all HTPC
>Simplify XBMC configurations
>HOW-TO Bitstreaming using XBMC
I refused to watch movie without bitstreaming HD audio!
Reply
#4
Question: Do you have your HTPC connected to your TV via HDMI?

If so disconnect your Cable connection to the TV. Comcast feeds from my TV, through my HDMI cable, through my receiver to my sub.
Code:
GRANT ALL PRIVILEGES ON `xbmc_%`.* TO 'xbmc'@'%';
IF you have a mysql problem, find one of the 4 dozen threads already open.
Reply
#5
It's possible that you have a ground loop in your setup, which gets worse when XBMC is running because of the increased power consumption of the HTPC.
Yeah it's a long shot, but most hums happen because of ground loops Smile

The reason that you only hear it through the subwoofer is because the hum is 50 hertz, and the other speakers have a high pass filter higher than 50 hertz.
Reply
#6
What's this 50 Hz crap. Smile
Code:
GRANT ALL PRIVILEGES ON `xbmc_%`.* TO 'xbmc'@'%';
IF you have a mysql problem, find one of the 4 dozen threads already open.
Reply
#7
It's the frequency of the mains voltage.
Reply
#8
All good answers. I think Darkscout was tongue-in-cheek referring to the fact that many countries use 60hz AC mains lol.

As mentioned, your AVR probably has 3-prongs so a dedicated ground, whereas your sub likely has two prongs and no dedicated ground. This would mean your sub uses a floating circuit (no ground) and thus can be floating at something above 0V on the neutral.

Is the sub plug polarized (meaning one prong is wider and thus you can't reverse the plug)? Do NOT reverse it - see below:

A good thing to test if you have a meter or access to one is the neutral potential versus a true ground. Ideally there is no voltage difference between true ground and the neutral.

If there is more than a volt or two have an electrician properly ground your neutral - usually done to a copper water pipe with low resistence to true earth. It's a good safety practice regardless.
System: XBMC HTPC with HDMI WASAPI & AudioEngine - Denon  AVR-3808CI  - Denon DVD-5900 Universal Player  - Denon DCM-27 CD-Changer
- Sony BDP-S580 Blu-Ray  - X-Box 360  - Android tablet wireless remote - 7.1 Streem/Axiom/Velodyne Surround System
If I have been able to help feel free to add to my reputation +/- below - thanks!
Reply
#9
One other note: check that the amplification or gain on your sub is not set to max - for many subs this high gain makes it very sensitive to stray currents. Usually try set it to halfway and then adjust the signal from your amp to your tastes.
System: XBMC HTPC with HDMI WASAPI & AudioEngine - Denon  AVR-3808CI  - Denon DVD-5900 Universal Player  - Denon DCM-27 CD-Changer
- Sony BDP-S580 Blu-Ray  - X-Box 360  - Android tablet wireless remote - 7.1 Streem/Axiom/Velodyne Surround System
If I have been able to help feel free to add to my reputation +/- below - thanks!
Reply
#10
DDDamian Wrote:All good answers. I think Darkscout was tongue-in-cheek referring to the fact that many countries use 60hz AC mains lol.

However I can check the hostname people posted from so I know the mains frequency of the poster with reasonable certainty :p
Reply
#11
bobo1on1 Wrote:However I can check the hostname people posted from so I know the mains frequency of the poster with reasonable certainty :p

And we had it pegged as telepathic-guru omniscience! :p
System: XBMC HTPC with HDMI WASAPI & AudioEngine - Denon  AVR-3808CI  - Denon DVD-5900 Universal Player  - Denon DCM-27 CD-Changer
- Sony BDP-S580 Blu-Ray  - X-Box 360  - Android tablet wireless remote - 7.1 Streem/Axiom/Velodyne Surround System
If I have been able to help feel free to add to my reputation +/- below - thanks!
Reply

Logout Mark Read Team Forum Stats Members Help
Subwoofer buzzes/hums when XBMC is open0