When your subwoofer is in perfect shape, it delivers heavy bass. If it starts producing a humming sound, you need to act fast to fix it.
Something is going wrong. Many people begin by unplugging the input devices such as an amp or AV receiver to find out if any of them has a default. That is a great troubleshooting tactic.
But what will you do to fix the subwoofer when there is still a hum after removing the input? We have compiled this easy-to-follow guide to help you troubleshoot to establish the cause of the hum in this case and fix your subwoofer hum when no input is connected.
Trouble Shooting Subwoofer Hum No Input Step By Step
There are numerous potential causes of subwoofer hum.
On the other hand, here is what you need to do to detect the cause of the humming noise:
1. Check the Subwoofer’s Connection
The power plug’s orientation. If the power plug is reversed in the electrical socket, it can cause a hum in the sub.
The prongs are normally not equal in size. As such, check for the sign that one of them is wider and plug them in accordingly. You can also switch around the cable end that connects to the back of the sub as well.
Also, consider if components share one source. If this is the case, the two-prong AC plug can be the cause of the noise and not the subwoofer.
2. Check Whether Signals Bleed Over/Interference
Signals often bleed over and cause subwoofer hum if the audio and power cables are bundled together which is quite common.
A great way to manage your cables is to use a cable management rack. This prevents the bundling of the cables and prevents the bleeding of signals between different cables.
For example, the Rack Mount Horizontal Cable Management rack is a pretty good choice.
3. Consider Ground Loop
A ground loop is another major cause of subwoofer hum. Normally, to establish whether this is the source of the problem, you would need to check whether you have connected at least two of your devices to a common ground through different paths.
However, it is important to note that the ground loop is often rare when all inputs are eliminated. This normally occurs when you connect the sub to a receiver and it causes issues with the cable TV connection.
In this case, there may be a grounding issue with your subwoofer’s power supply. A quick fix is to try to ground the power supply. Here’s how you do it:
- Connect one side of a wire to the metal chassis screw of your subwoofer and the other side to something metallic and grounded. This could be anything like a metal grill or water pipe.
- Check for humming issues again
4. Check The Subwoofer’s Internal Amplifier
In most cases, the 50/60 Hz hum is really due to a leakage from the power supply side into the sub’s amplifier.
Maybe a component is damaged or maybe there are loose connections or a similar problem. However, the most common causes of these issues are capacitors in the amp or the amp’s power supply that goes bad.
You needed to check these components first but ensure that you do a general check of the internal amplifier. If you find that the capacitors are the problem, replacing them with better caps will normally fix the problem.
In any case, your best here is to contact the manufacturer for a replacement amp. Otherwise, it might just be too expensive to fix the sub and you may need to replace it altogether.
If you find that your amps issue was caused by a power surge, then please ensure that you get a proper surge protector for your subwoofer and all other home theater devices.
5. AC Line Noise
There are many home devices that cause interference on the AC mains, especially devices with a motor.
One common way to confirm this is you will normally see the effect on your TV in the form of jagged lines.
There’s, of course, one easy solution to this, turn off all those devices while the sub is blasting. Another way to fix this is by wrapping the subs power cable around to create a power choke using a ferrite ring as displayed above.
Quick Fixes For Subwoofer Hum With No Input
Once you have troubleshot the problem, you will know the exact cause of the noise. In some cases, you may end up fixing it during the troubleshooting stage without any difficulty.
But in others, you may need to try many different options until you successfully eliminate the problem.
The common techniques you can use to fix the hum include:
1. Reverse the Orientation of the Power Plug
If you notice that one of the prongs is wider, then you can tell with a high degree of accuracy that there is a problem with the power plug’s orientation.
Fixing this is perhaps the easiest. Change the connection polarity of the subwoofer by reversing the power plug’s orientation. It is easiest to use an AC ground adapter with uniform-sized prongs. You can find these adapters at your local home improvement store.
In some instances, changing the polarity of the connection may not be enough. For that matter, if your first attempt to fix the noise fails, consider reversing other plugs.
This is usually a problem if the components of your sound system share the same source of power. To solve this, be sure you reverse the other plugs’ orientations one by one. If this is the only hitch, that simple action will fix the subwoofer hum.
2. Separate the Cables
If you noticed during the troubleshooting period that your power and audio cables are clustered in bundles, this could be caused by the subwoofer hum.
The proximity can cause the signals to mix up and cause the subwoofer to hum. But you can also ensure that the fields that the moving current creates do not interfere with each other by increasing the space and fixing the sound.
Due to space limitations, you may not be able to stop the electric fields from interfering. If you are encountering this, you should upgrade your audio cables. Choose cables with an advanced shielding mechanism, and you will be able to fix the subwoofer hum successfully.
3. Switch Outlets
If you detect that a ground loop is responsible for the subwoofer hum, switch the outlets that you use.
You can move your subwoofer to a different AC circuit in the room. In case you cannot reach an extension wall separate from your sound system, use an extension cord, and you will fix the ground loop.
But there are occasions when they may fail to resolve ground loops. If the grounding techniques fail to serve the intended purpose, purchase an audio isolation transformer. Install it to solve the subwoofer hum. Again, if you eliminate all subwoofer inputs, you are less likely to experience the ground loop.
4. Fix or Replace The Amplifier
At the end of the day, if you discover that the amp is the problem, you should attempt to fix whatever issue it has such as a damaged component. If that doesn’t work, you need to replace the amp altogether.
Which Are the Subwoofer Inputs?
In most cases, subwoofers use LFE (low-frequency effects) input cables. Many others are using the right and left inputs (RCA connectors).
The sound system sends low frequencies through the left and right channels in the latter case.
In the practical sense, you are less likely to use the R and L inputs if your subwoofer has the common LFE cable option. But the subwoofer can have the inputs whether it has the LFE cable option or not. If the device lacks the LFE option, you can use the L and R inputs.
The work of the LFE is connecting the subwoofer to the receiver. Since the sole purpose of a subwoofer is to produce low bass tones, you need to incorporate a transmitter of low-frequency audio waves into the system to get quality sound. The right and left channels are usually combined in this single cable.
Car Subwoofer Makes Loud Humming Noise
To troubleshoot this problem, check the RCA cables. The cables provide a musical signal from your car stereo right into the amp and convert them into a bigger and louder signal. Sometimes, the cable becomes loose, or the shielding becomes brittle due to cold weather. Run a spare pair of RCA down the side panel and check if it fixes the problem.
If changing the RCA does not fix the problem, check the grounding spot for weakness and poor conductivity with the chassis metal. Clean the metal with sandpaper and connect the ground loop to bare metal to improve conductivity.
If the subwoofer still hums, check if the power and RCA cables are too close together. If the two cables are running down the same panel, try running them separately and check if the problem is solved.
The fact is persistent humming can be produced from the subwoofer, whether you have connected an input device or not.
You can disconnect all the inputs and leave the speaker cables, AC plug powering the unit, and loudspeakers but still hear the 60-hertz hum. In many cases, only plugging the unit into the AC wall outlet can be the direct result of this low-level noise.
Whether your subwoofer hum with no input has been caused by electrical defects, induced noise, ground loop noise, or ‘upstream’ issues, you can use this simple guide to troubleshoot the exact cause of the problem. Use your findings to help you fix the hum, but remember the problem could be caused my more than a single issue.
Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics.