Subwoofer question

[Confused7]

Hi everybody,
I have recently bought a 2.1 Altec Lansing system. Is it normal for the subwoofer to make a constant buzz when the PC is off and the speakers are off? It is not really noisy but it is steady and constant. Is there something wrong with the subwoofer or is this normal?
Thanks

[ski]

Your subwoofer hum may be caused by a 'ground loop'.

Some things to do in order to prevent this from happening are locating your subwoofer's power and speaker cables far away from other power cables and coaxial TV cables, laying its cables perpendicular(not parallel) to other power and coaxial cables when it's impossible to keep them separated, plugging it into an outlet that does not have another electrical component connected, and not plugging it into an outlet that's on the same circuit as a component with an electric motor(air conditioner, refrigerator, furnace, dehumidifier, etc.) or flourescent lights.

[Sylvander]

I assume these speakers have their own built-in amplifier?
You say "the speakers are off".
Are you saying their amplifier is receiving no mains power?
So the amp is "dead"?
I could understand this if the amplifier is "live" and something is affecting the signal input line to the amplifier.
The only way the speaker can generate sound output is if the signal leads to the speaker from the amplifier are not "dead".
I used to use amplifiers a lot and it was quite common to get hum if their was something amiss with the signal input lead to the amp. To simulate this just touch, with your finger, the end of the amplifier's signal input jack. You should hear a reasonably loud hum. Anything that produces a partial short of the signal lead to the shielding lead would produce hum. A total short produces really LOUD hum. They need to be totally insulated from each other. Perhaps when the PC is switched off, but the amplifier still has power, the separation/isolation of one lead from the other is not good enough. I'm thinking the imperfection is within the PC's sound card, and it only has effect when the PC is off.

[Confused7]

Thanks for your answers.

I hadn't noticed that this noise is made when the speakers are on too. But it is not really loud to notice it if music is played. Generally there's no problem with the performance of the speakers. I checked what ski mentiones but there was no change. I also disconnected the speakers from any audio device and just plugged them in and turned them on. The noise persisted. So I assume this is not a problem of the sound card or the cables. Can this be just normal for the subwoofer or is there some problem with it?

[Sylvander]

There has always been the possibility of the problem of unwanted sound ["noise"] versus wanted sound ["sound"].
"Noise" is just sound that you don't like/don't want [like "weeds" being plants that you don't like, or "terrorists" being freedom fighters/political activists that you don't like].
Hence amplifier/speaker systems have their "Sound to noise ratio" measured [it should be about 65 Decibels ( the sound is 65dB louder than the noise)].
That's so that when you are listening to what you want to hear, the background noise is effectively unable to be heard so does not intrude.
Good sound systems keep the noise level so low it cannot be heard, poor systems don't. What's the S/N ratio quoted for the system?
Sometimes you can hear both hum and hiss, probably depending on the tone settings. Bass brings out the hum, and treble brings out the hiss. These are more noticeable with the volume high and no "sound" playing. As soon as you play some "sound" it drowns out the "noise" [or should]. Turn down the volume and the "noise" becomes minimal. That's why the relative levels are what's important. The perfect amplifier would never produce any audible "noise" no matter what the level of "sound". Is that a practical impossibility I wonder?

[ski]

plugging it into an outlet that does not have another electrical component connected
Actually, that suggestion which I made in my previous post is incorrect.
The subwoofer should be plugged into the same outlet as other devices so that they all have a common ground(assuming that none of the other devices connected to that outlet or to that outlet's circuitry either use an electric motor, are flourescent lights, or are light dimmers).
For example, if your computer and its peripherals are connected to a surge arrestor which is in turn connected to a wall outlet, then the subwoofer should be connected either to the surge arrestor or directly to the same wall outlet.

[pop pop]

What you are describing definitely sounds like a ground issue, especially if the hum or buzz is constant. At normal levels (volume settings), without music or whatever, there should ideally be no perceptible sound out of the speakers at all. Of course, if you crank the volume up to max, you'll hear a hum on the lines even with a perfect ground. An intermittent buzz or click could be interference induce by something like a cell phone (my Klipsh Promedia do this).

The ground issue could be within the speaker, the external wires, or possibly inside your case.

Try different speakers, if you have them, try different wires, try a different sound card. If it turns out to be the speaker itself, take them back. If it's wiring, assuming the wires are standard, just replace them. If the issue is in the case, you have to figure out what to do there.

One other thing--the wiring--does it use the RCA connectors or stripped wires into clips on the subwoofer? If it uses stripped wires, make sure you have red (or striped or whatever) connected to red and black/solid connected to black. The reasoning there should be obvious and it's something that can be easily overlooked.

[Fruss Tray Ted]

I also disconnected the speakers from any audio device and just plugged them in and turned them on. The noise persisted.

Is the plug a 3 prong? Try a 3 to 2 prong adapter on it to effectively 'lift' the ground (round pin). If it doesn't help, return it to normal.

[Sylvander]

I have a faint recollection of this effect being fairly typical, and most noticeable on very powerful [loud] amplifiers.
I've just reproduced it in a lesser form on my own small speakers.
If I disconnect the amp input plug from the sound card line output socket and turn up the volume to max, I can just hear faint noise [hiss/hum] if I put my ear right up to the speaker [I'm not yet deaf though I'm getting there].
If I then plug it back into the socket the noise reduces to become practically inaudible.