Speaker hum

[gogreen]

When I shut down my computer and the room is silent, I notice the speakers humming. Doesn't seem to affect the sound otherwise. Lots of crossed wires on the floor behind the computer, but I've tried different ways to isolate the speaker cables and power cord, to no avail. Logitech Z2300 speaker system. Any ideas on why I'm getting this hum, and how to stop it? Thanks.

 

[Mashed1316]

Is your computer near to one of those fluorescent lamps?

 

[zigzag3143]

When I shut down my computer and the room is silent, I notice the speakers humming. Doesn't seem to affect the sound otherwise. Lots of crossed wires on the floor behind the computer, but I've tried different ways to isolate the speaker cables and power cord, to no avail. Logitech Z2300 speaker system. Any ideas on why I'm getting this hum, and how to stop it? Thanks.

\


Hums are usually a grounding issue. Is the computer and speakers grounded correctly into a surge strip or its equivalent?


Ken J

 

[Mashed1316]

When I shut down my computer and the room is silent, I notice the speakers humming. Doesn't seem to affect the sound otherwise. Lots of crossed wires on the floor behind the computer, but I've tried different ways to isolate the speaker cables and power cord, to no avail. Logitech Z2300 speaker system. Any ideas on why I'm getting this hum, and how to stop it? Thanks.

\


Hums are usually a grounding issue. Is the computer and speakers grounded correctly into a surge strip or its equivalent?


Ken J

Hey Ken, actually "Hum" is not a grounding issue, that's called a "Hiss", "Hum" is an oscillation of the AC at the frequency of mains electricity (60 or 50Hz)

I'm definitely sure it's not a grounding issue because that would sound like a high pitch hiss that could go away with touching the "non (or poor) grounded" spot...

 

[gogreen]

Zigzag3143 and Punkster: Thanks. No fluorescents near the computer or in the room, in fact. I had the speakers power cord plugged into a grounded strip at first--still humming. Then I plugged into a wall socket--still humming.

 

[Dwarf]

Hum can be caused by a problem in the power supply allowing noise to pass through and be amplified. This is a filtering problem, and the common way to eliminate it is to add a coil (choke) and capacitor as follows (the use of ferrite beads on the power leads may also prove benficial):



A standard PSU as found in speakers consists of a transformer, a rectifier and some form of power conditioning/smoothing (filter). This filter is often just a single capacitor across the rectifier output. The job of this capacitor is to store energy and to supply it to the rest of the circuitry. With reference to the above image, the dotted waveform represents the output from the rectifier. As you can see, this is far from smooth. It is the job of the capacitor to store some of the energy that is supplied and to release it to the rest of the circuitry when voltage level of the rectifier output drops (as it does on a cyclic basis). Even the PSU found in computers suffers from this, although the effects are very much minimised because of the higher frequencies involved (the higher the frequency of the voltage pulses on the input, the smoother the filtered output will be).

Again with reference to the above image, the closer to horizontal that we can get the filtered output, the less noise will be imparted to the rest of the circuitry. This is done by selecting appropriate value components for L and C. In addition, the use of ferrite beads on the input/output leads of the filter will prove beneficial.

Amplifier/speaker hiss is usually caused by having a floating input with the gain turned right up. The effect can be exacerbated if excess hum is also present.

One way to reduce this is to ensure that the amplifier/speakers is plugged into the same power strip as the rest of the system and to ensure that the gain is not set too high.

 

[Aphelion]

Dwarf nailed it..... most inexpensive computer speakers have shoddy power supplys I corrected 90% of the hum in a cheap set just by beefing up the filter capacitors.

Ap

 

[gogreen]

OK. I might be in way over my head here, but how do I beef up the filter capacitors?

 

[zigzag3143]

When I shut down my computer and the room is silent, I notice the speakers humming. Doesn't seem to affect the sound otherwise. Lots of crossed wires on the floor behind the computer, but I've tried different ways to isolate the speaker cables and power cord, to no avail. Logitech Z2300 speaker system. Any ideas on why I'm getting this hum, and how to stop it? Thanks.

\


Hums are usually a grounding issue. Is the computer and speakers grounded correctly into a surge strip or its equivalent?


Ken J

Hey Ken, actually "Hum" is not a grounding issue, that's called a "Hiss", "Hum" is an oscillation of the AC at the frequency of mains electricity (60 or 50Hz)

I'm definitely sure it's not a grounding issue because that would sound like a high pitch hiss that could go away with touching the "non (or poor) grounded" spot...

While no expert the last 5 articles I have read including the IEEE say

A one-volt difference, while seemingly insignificant, can cause large loop currents to flow through the ground conductor of the signal cable. Depending on the circuit configuration of the audio hardware, the audio signal impedance and the impedance of the signal cable ground, the currents may cause induced voltages in the audio circuitry. This is a source of the familiar 'hum' problem.

 

[gogreen]

OK, zigzag3143. And how do I solve the problem? Thanks. I get the feeling that curing this problem could be more complicated than I suspected.

 

[zigzag3143]

OK, zigzag3143. And how do I solve the problem? Thanks. I get the feeling that curing this problem could be more complicated than I suspected.

You might want to google audio hum yourself so you can choose the solution that will work best for you. There is a somewhat complicated description of the fix here

Avoiding Ground Loop Hum

There are devices (isolated, impedance balancers, etc) but more often than not if you make sure all the cables are solidly grounded and hopefully the computer as well, it may minimize it.

Also, this type of noise is usually more prevelant in spkr sys with sub woofers. If the sub is ampliefied I would start there.


ken J

 

[gogreen]

OK. Thanks, Ken J. Yes, the Logitech Z2300 speaker system includes a subwoofer. I'll have to move some things around and check all that's been suggested here. Thanks again.

 

[Aphelion]

OK. Thanks, Ken J. Yes, the Logitech Z2300 speaker system includes a subwoofer. I'll have to move some things around and check all that's been suggested here. Thanks again.

Do you have any small wall-wart power adapters in the vicinity of your speaker wires?

Are the speakers plugged into the same power supply as the computer, the same wall outlet? Also, does the speaker system power supply have a 2 or 3 prong (grounded) plug.

The Logitech you own is a well built system so I doubt if you need to deal with beefing up filter capacitors.

Ap

 

[Aphelion]

OK. Thanks, Ken J. Yes, the Logitech Z2300 speaker system includes a subwoofer. I'll have to move some things around and check all that's been suggested here. Thanks again.

Last on this..

If the Logitech speaker system has a three prong plug, use a ground lift adapter (3-prong -> 2-prong) and see if that eliminates audible hum.

Ap

 

[gogreen]

The speakers have the newer 2-pronged plug. The speakers aren't plugged into the same wall outlet.

 

[krokusnat]

The problem is the insulation surrounding the speaker wires isn't sufficient enough for all the electricity that the computer is generating from the power supply and other electronics and the hum is the sound of electricity penetrating you insulation and rendering it audible through the speakers. Most computer speaker manufacturers don't consider that. The only solution is to buy a high quality sound system for the computer one that is made for that type of environment...cause I wouldn't be breaking out the black electrical tape to beef it up, also speakers that plug into the outlet on the back of the motherboard are very susceptible to noise cause the electronic components used to create the outlets aren't of high enough quality...grounding won't get rid of this noise....speaker magnets are wonderful tools in amplifying the sound of electricity...

I forgot that one way to help the situation is to turn the sound down on the computer to about 50 percent and make sure you don't have microphones un-muted and things of that nature also turn the speaker volume down so not so much electricity is amplified....