Yes, the value of a good subwoofer is appreciated by everyone with a home theatre system. However, you might have another low-frequency signal which is found in every home, which may not be so pleasing to listen to. This is the 60-cycle hum of your AC power lines. In a perfect world, power cannot get into the audio signal path, and hence our world is just far from perfection.
Since the subwoofer intends to amplify low-frequency signals, when it hums, it can hum very loudly when the receiver is off. This article will take you through ways to find out and get rid of the hum in your subwoofer when the receiver is off.
Sometimes “brute force” way of getting rid of the 60-cycle hum is just filtering it out, but it is not the best way to solve the problem. Moreover, for you to be able to get rid of him when the receiver is off without throwing out some desired audio at the same time, first, you need to understand what the possible causes are
There are four likely reasons why subwoofer hum when your receiver is off; some of the possible causes;
- Subwoofer electrical defects;
- Induced noise around the cables;
- Ground loop sound, which comes from the different potential ground at the subwoofer or receiver; and
- Sound arising from other components upstream of the subwoofer.
In most cases, things that fix one of these issues may not solve all of them, and it is possible to have many factors contributing to your issue, so if some of the things help, then it does not resolve the problem, keep on trying.
How to fix the subwoofer hum when the receiver is off?
Unfortunately, in most cases, the cause of the subwoofer hum is the subwoofer itself. All audio reproduction devices that switch off of your regular AC power can tame the 60-cycle sound in the power supply; it can convert it to a very good DC voltage, then protect audio circuitry from power supply sufficiently and prevent subwoofer hum from reaching the signal path.
However, internal failures have a probability of messing up. This is one of the best ways to detect: disconnect everything from your subwoofer except power, then switch it on. If it still hums yet nothing is going on, then the problem could be with your sub, which may require replacement or repair.
1. Induced noise
Induced 60-Hertz sound is a hum that may come to an audio system through proximity to power cables. This can happen internally but commonly, and the bad routing of cables causes it. Most people have routed audio interconnect and power cable through just the same conduit.
The currents moving in your cable can create a field around the cable, then it can cause a similar current to flow to nearby conductors. Induced sound, which is entering through cables, is simple to fix.
The way to understand how to fix it is through the square of- the distance rule: the intensity of the magnetic field fades by the square of the distance from where the source is. A power line that is one inch away from the subwoofer interconnects is inducing some signal in it.
The induced signal will be quarter as strong at two inches, eighth as strong at three inches, and so on-The farther you separate them, the weaker the effects will be, so it is advisable to move some cables then see what happens. If you have a power cable lying just under a sub cable, then separation by a couple of inches can have a profound difference.
However, induced sound may be trickier than that because the issue is occurring inside the equipment. If you isolate power circuits badly from the line level, a powered subwoofer when the receiver is off, maybe something that does not work with cable placement will affect. If you are lucky that the problem is not an internal one, then this solution will address it.
2. Ground loop between receiver and subwoofer
It is a very common cause for subwoofer hum when the receiver is off. A ground loop current flows then attempts to solve the hum issue, which works well for induced sound, but will not be effective against ground loop sound.
The ground loop issue develops where we have differences in ground potential, maybe between pieces of devices, which can cause a small power current to pass through lines that connect the two. The flow on a circuit which is not balanced is in your signal path, so it gets amplified as if it was part of the original signal.
The ground loop can be easily solved without having to spend any money on the issue. The secret is to have all the grounds to have similar potential. It simply means getting them all plugged in the same power circuit. It is a matter of ensuring that you are using modern, earth-grounded circuits at every point in the system; hence you will have resolved the problem.
If you find out that you have a serious wiring problem at your home, just consider contacting an electrician.
3. “upstream” issues
In a situation whereby the above procedure does not resolve your issues, it is high time to broaden your search. Since the subwoofer hum can be isolated and its direct link to the receiver, the other distinct probability is that your hum is having its way to the audio stream further upstream. Some of the internal electrical defects, induced hum, and ground loops can develop anywhere in the system.
Firstly, check if the hum occurs only when the receiver is turned off to a particular source. If it does, it is a clear indication of where the issue could be arising from. Sometimes, under some conditions, sound can arise from the source you are not using.
Try to unplug all the sources, then reintroduce them one at a time; as you do that, check whether you have hum on that source or any other that you have reintroduced.
A good subwoofer will not hum when the receiver is off; however, depending on the cause of the hum, you can fix the issue simply by following the above procedure.
In a situation whereby you find that it is more complicated for you to fix the problem, just contact an electrician to help you on how to fix the problem.
To fix a subwoofer hum, you should watch this video below;