Subwoofer pulsing sounds can be quite annoying. If you are experiencing an annoying pulse sound from the subwoofer, almost like a rapid heartbeat, we will guide you on fixing it in this article.
For many people, this pulsing is a rhythmic “heartbeat” sound that may even occur when the AV cable is disconnected and the only cable running to it is the power cable. For many people, their subwoofer pulses like a heartbeat even on pause or when muted.
Typically, your subwoofer may be pulsing like a heartbeat due to bad media devices, a defective receiver/amplifier, defective capacitors or other components, incorrect frequency settings, WiFi interference, bad grounding, or worn-out cables as well as bad fuses.
Below are the steps you should take to fix this issue. Firstly, don’t assume that the sub itself is the problem. You may very well replace your sub with a new one and still have the same problem!
Please note that you should not modify the subwoofer in any way if you plan on returning it under warranty.
1. Disconnect All Media
The first step you want to take is to remove all media devices and rule it out if it is not causing the problem.
This means you should remove all media devices that you may be using and see if the subwoofer is still pulsing while no sound is playing. This could include DVD players, Blu-ray players, Alexa, PCs, etc.
A common example is if you are using a computer as a media source. A common issue here that causes pulsing sounds is the audio chipset hardware that may be damaged or the audio driver may be corrupt.
If a computer is causing this problem, try reinstalling the audio driver from the official site of your laptop’s brand.
For a simple fix, you could also turn down the system sounds to zero. The disadvantage here of course is that you will not hear other system sounds from the PC.
2. Rule Out The AV Receiver
If the subwoofer is still pulsing after you have disconnected all media, the next step is to rule out the receiver.
It is the same idea really if you remove the receiver connection and the pulsing sound goes away, then clearly the receiver is causing the problem.
Just disconnect the RCA line-in or the subwoofer cable connection and listen for the heartbeat pulsing sound.
If you have determined that the receiver is the problem, then you may have a defective receiver that needs to be checked out.
Disable AVR Bass Management
Do you have bass management enabled on your AVR? In other words, is your AVR controlling the LFE?
If so, can you turn it off, or set it to bypass or full range so that you get the full range to the sub and use the sub’s crossover? Just as a test.
3. Check The Amplifier
If you have an amp in your setup and you have determined that the receiver is not the problem, it’s time to check the amplifier.
For a quick test, simply throw in another amp if you have one. You could also connect the receiver directly to the sub and bypass the amplifier.
If the issue is occurring in a car subwoofer, check if your amplifier is going into protect mode, especially when the volume is turned up. if the music is cutting in and out with the pulsating heartbeat, then this is the likely problem.
Now, why does this happen? Well, your amp will go into protect mode via DC biasing meaning you are giving your sub a full DC rail as fast as the switched-mode power supply (SMPS) can create it.
However, the problem is that the protection circuitry detects that there is a DC signal on the output, and then resets it.
This is normally caused by a defective power supply or defective electronic components such as transistors, resistors, or operational amplifiers.
Check The Amps Capacitor
Capacitors are a common electronic component in audio devices. These components store up and release electrical charge as necessary.
These cycles of storing and releasing charge can “wear out” your capacitors over time. If you have the electronics technical know-how, take some time to go through the capacitors on the circuitry and replace the defective ones.
You can easily use a scope and capacitor tester to find the defective caps. It’s important to remember that some of them come in pairs.
4. Change Frequency Settings (Subwoofer Crossover)
For some subwoofers, you may experience this issue if your lowpass filter crossover is set too high.
The lowpass filter is simply a device in your subwoofer that limits the frequencies that the sub plays to low bass frequencies.
This means that if your subwoofer low pass filter is set to say 80Hz, then the filter will not allow any frequencies above 80Hz to play through the subwoofer.
Many people set their subwoofer LPF of LFE to 120Hz. This can cause pulsing as the subwoofer is not able to handle these high frequencies properly. Take some time to learn more about setting the correct subwoofer crossover frequency.
Adjust your lowpass knob on the sub down to 80Hz to 90Hz. Just adjust within this range until the heartbeat pulsing goes away and the sub sounds good enough to you.
We admit, for some subs, if you turn the LPF all the way down, the bass may no longer be adequate. To fix this problem, you can try adjusting your receiver bass management options and the amplifier gain.
5. Kill All Source of Interference
If your subwoofer is connected via wireless whether, by WiFi or Bluetooth, you need to ensure that there is nothing interfering with the wireless signals.
This could include the WiFi router, computers, phones, Bluetooth speakers, and more. check everything!
In one instance, one of our clients had a Chromecast plugged into the back of the receiver that was causing the problem.
6. Check Ground and Switch Cables and Outlets
Grounding problems may also be causing your subwoofer heartbeat pulsing issues. First of all, grounding is very important for your home theater system.
This is important not just for performance, but also to protect you in the event of shorts in the system and to also protect your system in the event of electrical surges due to shorts or even lightning!
For your home theater, ensure you have a three-pronged cable and if you have any extensions, ensure they are all three-pronged.
If grounding is the problem, switch out the 2 pronged cables for 3 pronged cables or get a 2-to-3 prong converter or a line conditioner.
If your issue is with a car subwoofer, grounding problems are a common cause for heartbeat pulsing and thumping as well.
7. Check The Power Supply and Power Cables
If you have ruled out grounding issues, check the power supply.
In some cases, the issue may even be with your room circuitry! A quick check is to use an industrial gauge cord and pug it into a power outlet from a different room.
An old or worn-out power cable can cause subwoofer pulsating problems as well. A failing supply voltage is normally caused by high resistance in the power cables. Switch out your old power cables for new ones and see if that helps.
If your issue is with a car subwoofer, hook up the sub straight up to the battery with short cables to test it. You can also check with a multimeter how much voltage is across the supply voltage terminals.
8. Switch Out Components
If neither the receiver nor amp nor cables and such are not the problems, it’s time to switch out other components and rule them out as you go along.
By this, we mean you should switch out the various components of your audio system. For example, switch out the cables and other special devices you may have connected, like Bluetooth transmitters and so on.
9. Check Fuses
A fuse is an electronic component used to cut off circuitry in the case of a power surge. This prevents circuitry from being damaged by a power overload.
If you had a recent power surge due to bad cables or shorts that have since been fixed, you may still have blown fuses within your system.
You can get a fuse tester like the simple JASTIND Heavy Duty Automotive Circuit Tester [Amazon Link] or even use a multimeter to test the fuses within your subwoofer and your amp.
However, don’t just replace the fuse. check to see if there is a shorted wire within the device that caused the surge that damaged the fuse in the first place.
10. Return It Or Send Back Under Warranty
If you have tried everything and still no luck, we recommend that you return the subwoofer to the manufacturer if it is under warranty.
Of course, if you intend to return the subwoofer, you cant disassemble it or change its internal components in any way. This is a solution for someone who is not familiar with electronics or who does not wish to pay a technician to fix it.
In most cases, if the defective subwoofer is a result of a manufacturer’s defect, they will send a replacement. For example, LG is known to have pulsing issues and subwoofer hum issues with some of their subwoofers, and Klipsch is known for its amp failures. In such cases, they will replace the device in short order.
In such a case, we do recommend that you pay to upgrade to another sub to try and avoid this issue with the same sub occurring again.