If you've ever touched the end of a cable that was plugged into a speaker, you've likely heard a buzzing sound. Common examples include handling the auxiliary cable in the car when trying to plug your phone in or handling a patch cord when plugging it into an electric guitar while the amp is on.
Why do speakers hum when someone touches the plug, jack or cable? The human body is electrically conductive, so touching the conductor (the plug or even the cable itself in poorly insulated cable designs) of a connected cable will effectively produce a circuit between the speaker and us. This circuit causes the speaker to produce a hum.
Let's discuss why this is with more scientific detail to better understand why touching the plug and/or cable of a speaker will cause the speaker to hum.
A Primer On Speaker Transducers
Before we get started, let's quickly define how a speaker works.
A speaker is a transducer of energy. This means it converts one form of energy to another form of energy.
More specifically, speakers turn electrical energy into kinetic energy.
To get even more specific, speakers are designed to take electrical energy in the form of audio signals (alternating currents) and turn them into diaphragm motion that mimics the waveform of the AC signal. This diaphragm motion pushes and pulls air to produce mechanical wave energy, which is the type of energy that sound waves are made of.
So to simplify it, speakers take AC voltage and use it to produce sound.
To learn more about audio signals and sound waves, check out my article What Is The Difference Between Sound And Audio?
Typically this happens by connecting a speaker to an amplifier or directly to an audio source.
However, there are electrical energy sources other than AC audio signals that can have an effect on the motion of the speaker's diaphragm and the sound waves the speakers produce.
So to understand why touching a speaker cable or plug/jack causes the speaker to hum, we must understand the following:
- Humming and buzzing is sound.
- Humans are electrical conductors.
For more information on how speakers are defined as transducers, check out my article How Do Speakers & Headphones Work As Transducers?
With that primer, let's move on.
Typical Causes Of Speakers Hum
Below is a list of the typical culprits that cause speaker hum.
- Electrical ground loops
- Electromagnetic interference
- Faulty hardware (speaker, speaker cable, plug/jack or audio device)
Electrical Ground Loops
A ground loop is caused by connecting electrical devices in a way that provides multiple paths to ground.
Ideally, two points of an audio circuit should have the same ground reference potential. In a ground loop, these two points will have a different ground potential between them.
Let's say that two audio devices, a mixing board and an active speaker, are each properly connected to ground.
The mixing board's output is connected to the speaker's input via an audio cable.
This audio cable's shield (a conductor designed as “cable ground”; to protect against electromagnetic interference and provide a signal return path) connects to the ground of the speaker and the mixer to form a closed conductive ground loop.
The closed-loop includes the ground conductors of the active speaker and mixer power cords, which are connected through the power mains and the building utility ground wire.
The AC power mains have a frequency of 50 Hz or 60 Hz, depending on where you live in the world.
These power mains induce an alternating current through the resistance of the cable ground conductor and will cause a small AC voltage drop across the cable ground.
Because audio signals are AC voltages between 20 Hz – 20,000 Hz, the induced 50 or 60 Hz interference may be heard as humming/buzzing in the speakers.
Electromagnetic Interference
Note that radio frequency interference (RFI) is a common type of electromagnetic interference (EMI) that happens in the radio frequency range (30 Hz – 300 GHz) of the electromagnetic frequencies.
EMI will induce noise to an audio signal through means of electromagnetic induction, electrostatic coupling, or electrical conduction.
The flow of electricity will produce magnetic fields, and magnetic fields cause the flow of electricity.
The aforementioned power mains can cause electromagnetic interference and noise in the audio cable and the speaker, which will cause hum.
Similarly, nearby and distant radio wave transmission can cause interference, noise and hum in the audio conductors and, therefore, the connected speakers.
Related article: Why Speakers Hum/Buzz Around Cell Phones And How To Stop It
Faulty Hardware
Finally, a faulty piece of hardware can lead to hum and buzzing in the speaker. Faulty gear is may directly cause hum and buzzing, or it may make the audio path more susceptible to the EMI and ground issues stated above.
The Human Conductor
Electricity is everywhere, even in our bodies. In fact, our central nervous system requires electricity to send signals throughout the body and to the brain effectively.
Nearly all of our cells use electricity in some capacity with the help of electrolytes (namely sodium, potassium, calcium, and magnesium). Without electricity, humans couldn't think, act or sense the world around them.
Though we've evolved within electromagnetic fields, the magnetic fields and electricity of our environment do affect our “inner electricity.”
Our skin is, fortunately, the least conductive part of our electrical bodies. The skin’s normal resistance is high enough to limit the current through the body and protect us from externally applied electrical signals.
The relative dryness of the skin combined with its lack of both ions makes it a relatively poor medium through which the current can flow. Of course, the resistance can be lowered by wetting the skin.
That being said, the skin is affected by the electromagnetic and electrostatic fields it is surrounded by, and our bodies effectively antennae that pick up electromagnetic energy, which becomes a voltage on your skin.
The body also has its own capacitance, which means that it can hold onto electrical charge. The dissipation of this charge is the electrostatic shock we feel (after rubbing our feet on a carpet and then touching a doorknob, for example).
The bottom line is that it is possible for the electricity of our bodies to affect the sound a speaker would make.
Hum When Touching The Cable Plug Before Plugging The Speaker Into A Source
This is perhaps the question that brought you to this article. If a speaker is on and has a cable ready to connect to a source, why does the speaker hum when I touch the end of the cable?
An Example of this happening is plugging a patch cord into a guitar to connect the guitar to an amp in the on position. Another more relatable example is touching the end of the auxiliary cable in a car when the car stereo is already set to aux mode, and the volume is turned up.
As we've discussed, your body is electrically conductive. When you touch the end of the audio cable connected to a speaker, some electricity from your body flows through the cable's conductors and causes the speaker to produce sound.
But why is the sound typically a 50/60 Hz hum rather than a, say, a simple 1 kHz or white noise (as a few examples)?
We learned previously that the human body acts as an antenna to the electromagnetic fields around it and has a capacitance that allows it to hold onto electric charge.
We've also learned that the AC mains (whether 50 Hz or 60 Hz) produce constant electromagnetic radiation.
Our bodies pick up the electromagnetic radiation of the power mains, which effectively produces a voltage on our skin.
So, if we are to touch the end of the audio cable connected to a speaker, the 50/60 Hz AC voltage is transferred from our bodies, through the cable and to the speaker, which causes the speaker to produce the dreaded “60 cycle hum” (or 50 cycle hum, depending on your location).
Active speakers have built-in amplifiers that will effectively amplify the voltage from our bodies and make the hum louder.
If you were to touch another person (another antenna for the mains electromagnetic radiation), then the hum would get louder.
If we were to touch a grounded device, the voltage should dissipate from your body rather than get transferred to the speaker, which would eliminate the hum (or at least reduce the volume in the non-ideal world we live in).
Pro tip: it's always best to either turn the speaker(s) off or turn the volume all the way down before connecting anything to the speaker(s) (including your body).
Hum While Only The Cable Is Connected To The Speaker
Sometimes we'll have a speaker turned on but not connected to anything that will still produce hum/buzz.
This is because the speaker itself and its cables also act as antennas that will pick up electromagnetic interference from the power mains and other electromagnetic devices in proximity (wireless devices, nearby radio stations, etc.).
Hum When Touching The Cable While The Speaker Is Plugged Into A Source
If your speakers begin humming/buzzing when you touch the cable, then the cable is likely faulty or not shielded correctly. Again, the hum/buzz is from your electrical body transferring it induces electromagnetic radiation from your skin to the cable's conductors and the speaker.
Alternatively, if the speaker starts crackling or cutting out when you touch the cable that connects it to its audio device, there is likely an electrical or mechanical fault with the cable and/or its connections (jack and plugs) with the speaker and audio device.
Try troubleshooting by swapping the cable. If this doesn't solve the issue, try isolating the connectors by swapping the connected devices. The connector may require repair or replacement.
Hum Without Touching The Cable While The Speaker Is Plugged Into A Source
If the speaker hum/buzz by simply being plugged into your audio system, then you likely have an issue with one of the aforementioned factors that cause speaker hum. They are, once again:
- Electrical ground loops
- Electromagnetic interference
- Faulty hardware (speaker, speaker cable, plug/jack or audio device)
Troubleshooting these issues can be a difficult and tedious task and is beyond the scope of this quick article.
Even once the issue is narrowed down, solving the issue is often complicated and elusive.
Related Questions
What is audio cable noise? Audio cable noise is defined as any electrical noise that is not part of the intended audio signal. This noise is the flow of electrons in the cable that is not part of the audio. Noise is typically caused by electromagnetic interference, static electricity, handling noise and ground loops.
What causes buzzing in a 3.5mm jack? Sometimes the electrical connections in an audio jack can be faulty; the fit may be loose, or the plug and jack may be incompatible. This can cause buzzing and crackling. However, the more probable cause is electromagnetic interference and/or ground loop in the audio system that induces buzzing noise in the audio signal.
For more information on audio jacks, check out the following My New Microphone articles:
• Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks
• Are AUX (Auxiliary) Connectors & Headphone Jacks The Same?
• How Do Headphone Jacks And Plugs Work? (+ Wiring Diagrams)
• What Is The Difference Between A Microphone Plug And Jack?
Choosing the right PA speakers for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive PA Speaker Buyer's Guide. Check it out for help in determining your next PA speaker purchase.
With so many loudspeakers on the market, purchasing the best speaker(s) for your applications can be rather daunting. For this reason, I've created My New Microphone's Comprehensive Loudspeaker Buyer's Guide. Check it out for help in determining your next speaker acquisition.
This article has been approved in accordance with the My New Microphone Editorial Policy.
