I have two speakers and a subwoofer (powered - plugged into the wall) hooked to my computer. When I turn off the computer (speakers still plugged in) the speakers buzz. I've tried the same connection with an expensive sound bar and subwoofer and they do not buzz.

Typically that noise happens when computer and speakers have different ground levels, explained here. Are you sure that you did not also change anything in that regard, different outlets, etc? Is your pc connected to other devices, antennas, network switches, etc? Try connecting your speakers and computer at the same power outlet, with an extension cord.

Edit

http://www.soundonsound.com/forum/showflat.php?Number=984446

They are all connected to a ups battery back up. I tried plugging the speakers into a different outlet in a different part of the house. They buzz unless they are hooked to a computer that is running.

You mention the speakers buzz when the PC (I assume it is a Desktop) is switched off.

What happens when the PC power plug is removed from the electric socket (but the speakers are powered on and connected to PC)?

What happens when the speaker is isolated from the PC, meaning all the audio cables removed from the PC (but the speakers are powered on)?

Did you try a change of location?

Any other electrical appliances or wiring near by?

You could try connecting the chassis of the PC and a metal part of the speaker with a wire (just for a common ground).

Perhaps the polarity should be reversed on each speakers wire. Reverse them, one speaker at a time. If that doesn't help, the problem is probably that your electricity is not properly earthed, or grounded. Do you plug into a 2 prong or 3 prong outlet. Is that outlet, meaning the entire system grounded. Maybe you can run a wire off the back of the backup battery and ground this all, thus eliminating the buzz?

They are all connected to a ups battery back up. I tried plugging the speakers into a different outlet in a different part of the house. They buzz unless they are hooked to a computer that is running.

As has already been mentioned,

Buzz is likely when the input line is allowed to 'float', or when ground levels of the connected devices are different, or when unwanted additional paths to ground are present which allow non-audio currents to mix with audio signals.

Computers are an instant combo of the best and worst audio devices ever designed.

...but I would say your soundbar amplifier is of higher quality design, dampening the effect of the floating input when the computer is shut off or when its input cable is unplugged.

Your other amplifier most likely lacks circuit properties to reduce open circuit ground buzz.

If you eliminated a ground loop as per the posts above, it will just be because it uses a POS STK style amplifier chip - nothing can make them quiet.

Speaker wires are not sufficiently shielded not to pick up stray electromagnetic radiation radio, cell phone or wifi from your router if you use one!

Speaker wires are not sufficiently shielded not to pick up stray electromagnetic radiation radio, cell phone or wifi from your router if you use one!

No way - the amount of EMF/EMI required to make a typical 4-8 ohm loudspeaker buzz is so high, the OP wouldn't be posting here. It's just a shit STK amp.

50Hz filtering problem? As one post says if you have different earths you will get circulating currents

Thanks all. I changed all the plugs and tried different connections then I finally looked at the subwoofer volume control. I never touch the thing because the volume is controlled from my PC. There must be a short in it because after I whacked a couple of times the buzzing stopped. Again thanks all.

Thanks all. I changed all the plugs and tried different connections then I finally looked at the subwoofer volume control. I never touch the thing because the volume is controlled from my PC. There must be a short in it because after I whacked a couple of times the buzzing stopped. Again thanks all.

If any of the cables are screened make sure the creen is tied down at one end only.

Perhaps the polarity should be reversed on each speakers wire. Reverse them, one speaker at a time. If that doesn't help, the problem is probably that your electricity is not properly earthed, or grounded. Do you plug into a 2 prong or 3 prong outlet. Is that outlet, meaning the entire system grounded. Maybe you can run a wire off the back of the backup battery and ground this all, thus eliminating the buzz?

Don't have him wasting his time, reversing polarity will make no difference. Nor will trying to earth a two wire L/N supply if there is no actual earth. I would remove the PC Completely and test the speakers on their own, if they buzz they are junk, if not, then look at some way of putting a cable to ground the speakers to the chassis of the PC.

Poor connection from the 3.5mm jack? Maybe, you could hook a wire from the 3.5mm earth / negative and ground it out to the metal chassis of the pc?

Speaker wires are not sufficiently shielded not to pick up stray electromagnetic radiation radio, cell phone or wifi from your router if you use one!

Wi-Fi and GSM carriers are long way out of the band in question for audio, also of coures these systems have very low transmission power far below the requirement to buzz the speakers

Speaker wires are not sufficiently shielded not to pick up stray electromagnetic radiation radio, cell phone or wifi from your router if you use one!

Wi-Fi and GSM carriers are long way out of the band in question for audio, also of coures these systems have very low transmission power far below the requirement to buzz the speakers

Speaker wire, and speakers ...no. Unshielded line inputs that get amplified, yep.

When Blackberry phones started making their way into the hands of TV and Radio Broadcasters, we instantly had a nightmare on our hands.

Blackberry devices were causing serious interference for all manufacturers’ microphones.

The radio signal transmitted by digital mobiles penetrated right through the metal mic grille to be picked up by the mic capsule and circuitry.

That noise sounded like a digital horse galloping through your control studio.

The FET gate lead inside the mic capsule is particularly vulnerable to RFI/EM fields.

OP, glad to hear you found the cause.

In this damp environments, Rheostat or Potentiometers control metal contacts are open to air and can pick up oils, dirt or start to corrode.

But can keep the contacts clean by 'wiping' the contacts (quickly moving the knob from one extreme to other several times).

"after I whacked a couple of times" might also work ...but they don't put that procedure in the manual.

...last time I checked, getting 'whacked' was also a way they permanently fixed problems on the US east coast.

They are all connected to a ups battery back up. I tried plugging the speakers into a different outlet in a different part of the house. They buzz unless they are hooked to a computer that is running.

Open the master volume panel on your computer.

Tick the mute on Mic Volume. This should solve the problem.

Thanks all. I changed all the plugs and tried different connections then I finally looked at the subwoofer volume control. I never touch the thing because the volume is controlled from my PC. There must be a short in it because after I whacked a couple of times the buzzing stopped. Again thanks all.

Excellent! All the electronics and audio theory in the world floating around the post and you whacked it a couple of times. Loving it.

To quote an old saying, What is the difference between a technician and an engineer? A technician knows to hit it. An engineer knows WHERE to hit it.

A. switch polarity of plug by unplugging, rotate 180*, plug back in if receptacle compatible

B. phase your speaker wires...Google for explanation

They are all connected to a ups battery back up. I tried plugging the speakers into a different outlet in a different part of the house. They buzz unless they are hooked to a computer that is running.

Open the master volume panel on your computer.

Tick the mute on Mic Volume. This should solve the problem.

very helpful advice indeed, but only if he turns ant clockwise three times while snapping his fingers and reciting robert burns.

I cured a similar background buzzing by running a short wire from ground to the frame of the amplifier.

When you turn off the computer the amplifier input picks up interference and amplifies it.

Possibly from the inverters in the UPS system.

Could you power the amplifier from the computer so that it is powered off when the computer is?

(If it is a laptop it should not need a UPS as it has a battery).

I wish you had said hum not buzz, then I could have hit you with the pun 'because they do not know the words'.

Speaker wires are not sufficiently shielded not to pick up stray electromagnetic radiation radio, cell phone or wifi from your router if you use one!

Wi-Fi and GSM carriers are long way out of the band in question for audio, also of coures these systems have very low transmission power far below the requirement to buzz the speakers

Ever experienced a mobile phone ring near a desktop with a CRT screen?

Speaker buzz and the screen flicker is obvious - even before the 1st audible ring!

They are all connected to a ups battery back up. I tried plugging the speakers into a different outlet in a different part of the house. They buzz unless they are hooked to a computer that is running.

Open the master volume panel on your computer.

Tick the mute on Mic Volume. This should solve the problem.

It says mic not plugged in so no volume control.

USually a sign of eating too much Candy.

I cured a similar background buzzing by running a short wire from ground to the frame of the amplifier.

When you turn off the computer the amplifier input picks up interference and amplifies it.

Possibly from the inverters in the UPS system.

Could you power the amplifier from the computer so that it is powered off when the computer is?

(If it is a laptop it should not need a UPS as it has a battery).

I wish you had said hum not buzz, then I could have hit you with the pun 'because they do not know the words'.

Do you use Bees (B's) for speakers?

Thanks all. I changed all the plugs and tried different connections then I finally looked at the subwoofer volume control. I never touch the thing because the volume is controlled from my PC. There must be a short in it because after I whacked a couple of times the buzzing stopped. Again thanks

I like the sound of that, we already have (among others), "Spanking the Monkey", "Choking the Chicken" and not forgetting "Flogging the Dolphin" but lostoday I reckon you've found a real winner. Folks I give you:

"WHACKING THE WOOFER" l