Ground loops are among the most common causes of interference noise when using powered monitor speakers. This is because powered monitors often utilize a “safety ground” in their power cable, and since desktop computers also use a safety ground, a “ground loop” is liable to occur once these devices are connected to each other.
Image
Safety grounds (the circular pin on a North American 3-prong power cable) exist to ensure electricity has a low resistance path to the earth. Since electricity naturally seeks the earth through whatever path offers least resistance, they are effective at preventing electricity from traveling through less favorable conduits instead (such as a person).
Ideally, every safety ground would offer identical resistance. However, in the real world this is almost never the case. Temperature, humidity, electrical load, and other factors affect the ground potential of each outlet in subtle ways. These differences are usually non problematic when a piece of equipment is by itself, but when two or more devices are connected to each other they can create a ground loop, and that’s where problems arise. In this circumstance, the differences in ground potential between devices turns the ground wiring into a crude antenna, amplifying nearby magnetic interferences and introducing them to the signal. With speakers, this interference manifests in the form of an annoying hum or chirping sound.
Luckily there are many solutions to this problem, and we will cover a few of the most common below, most of which work by the concept of “breaking the loop.”
- In-line ground loop isolators are one way of breaking the loop. They work by breaking the direct current connection between components while continuing to pass signal. They are generally inexpensive and considered an ideal solution by many. The downside is that they can produce signal distortion. This distortion is very seldom noticeable when using purpose-built isolators, but however negligible, it is worth considering.
- Removing the ground from one or more of the devices also breaks the loop. This can be done by simply using a 2-prong power cable instead of a 3-prong. However, bypassing the safety ground can create an electrocution risk. As you could imagine, we file this solution under “not advisable”.
- A safe alternative to the above is to use an external DAC/amp which has an AC adapter power supply. These types of small power supplies rarely pass the safety ground through to its receiving device. For the DAC, this prevents it from being introduced to the loop. An added benefit of using an external DAC is they often provide superior sound quality to onboard motherboard audio.
- Balanced cables are considered a minimum requirement by most audio professionals, as they are resistant to many types of signal noise, including ground loop interference. By design, these cables separate the ground wire from the signal path, so although a ground loop exists, its effect on the audio signal will be reduced, if not removed entirely.
Note: Sometimes power conditioners and Uninterruptible Power Supplies (i.e. battery backup units) are mistakenly considered as a solution to ground loop interference. Although both of these devices serve their respective purposes, neither will resolve a ground loop interference problem. If they do happen to remove noise, it is likely the interference was caused by “dirty power”, and not a ground loop.
Ground loops have been well understood by humanity for over 50 years, but despite them being such an old and familiar problem, they remain an infamous cause of frustration for audio/video professionals today. Hopefully this article sheds some light on their nature, or points you in the right direction if you are experiencing one.