If you've ever cranked up the volume of your favourite songs in the car, you may have noticed audible speaker distortion. The speakers may have even been distorting without you noticing at all.
Why do speakers distort at high sound/audio levels? There are two main reasons why a loudspeaker would distort at high levels. The most common is that the audio source, itself, is distorted. However, speakers can also distort if their drivers are pushed to the extremes of their designed motion, in which case they behave non-linearly and produce distorted sound.
In this article, we'll discuss speaker distortion in greater detail, going into its causes and effects. We'll also touch on how distortion may or may not damage speakers.
What Is Distortion?
Audio distortion refers to any deformation of an output waveform compared to its input.
Speaker distortion, then, is technically only the difference between the waveform of the sound waves it produces compared to the waveform of the audio signal applied to its drivers.
This is rather difficult to calculate, considering sound and audio are two different types of energy.
To learn more about the differences between sound and audio, check out my article What Is The Difference Between Sound And Audio?
In practice, we typically consider speaker distortion as the audible distortion we hear in the sound emanating from the speaker. This isn't always obvious to untrained ears but is generally what we're referring to when discussing speaker distortion.
This distortion is largely a product of non-linear movement in a speaker driver.
The sound we hear from a speaker is dependent on more than just the speaker's accuracy as a transducer. It's also a function of:
- The original audio signal.
- The amplifier(s) between the audio device and the speaker.
- Cross-over networks.
- Physical damage in the speaker.
If any of the above factors produce distortion, then the speaker will likely sound distorted.
For more information on how loudspeakers act as transducers, check out my article How Do Speakers & Headphones Work As Transducers?
Disregard Power Handling
Power handling is a loudspeaker specification that refers to the maximum nominal amount of wattage the speakers can handle from an amplifier (measured in watts). However, this spec is rather useless without considering other specs and details of the loudspeaker.
Let's say a speaker has a specified power handling rating of 100 watts.
A 200-watt amplifier can still drive this speaker without sustaining damage or distorting so long as the volume is kept at a reasonable level.
This speaker can also be driven by a 50-watt amplifier, though there's no guarantee that the speaker will not distort or get damaged when turning the amp up too loud.
As a rule of thumb, if the speaker begins to sound distorted, turn it down!
All this is to say that speakers can distort when connected to stronger and weaker amplifiers. Distortion is less likely to happen when the speakers are properly matched to their amplifiers. More on this in the section titled Active Vs. Passive Speakers.
Why Speakers Distort At High Levels
Let's now examine the reason why speakers would distort at high levels.
First, “high levels” refers to the audio signal amplitudes applied to the speaker driver.
The most common form of speaker distortion actually has less to do with the speaker failing and more to do with the amplifier. This distortion is known as amplifier clipping and is described in the diagram below:
In the above diagram, we see that there is a limit to the amount of signal an amplifier can produce. This clipping voltage level is defined as +/– Vc.
The blue audio signal to the left is perfectly within the limits of Vc and is not distorted. However, the red audio signal to the right has been amplified beyond the amplifier's capabilities, and the signal has been clipped at its max positive and negative values.
Turning the volume up increases the amount of gain the amplifier applies to the signal. There is a threshold at which the amplitude of the output waveform exceeds the current or voltage capability of the power supply/amplifier. It's at this point that the top and bottom are “clipped” off the waveform.
This is exactly what is shown in the diagram above.
That explains the audible distortion in a speaker due to the overloading of the amplifier.
However, though not as common, it's also possible for the speaker to be overloaded rather than the amplifier.
The majority of speakers have a linear range of motion. As an audio signal is applied to the driver's voice coil, the driver should mimic the waveform of the signal to produce the appropriate sound waves.
However, if the voice coil travels further than it is designed to due to a higher-than-expected audio signal, then the motion can become non-linear.
This is particularly true at the extremes of the driver's movement, where the cone cannot push (or pull) any more air. This causes a discrepancy between the audio signal waveform and the sound waveform, which is effectively distortion.
Even worse is the banging and popping that can occur when the driver's motion causes the cone to slam against the housing of the driver.
That explains a single speaker, but the audio has the potential to become even more detrimental when crossover systems are overloaded.
Crossover systems/networks are used to split up the frequency bands of an audio signal and send those bands to the speakers that will best reproduce them.
For example, a crossover network could split an audio signal up as follows:
- 20 Hz – 100 Hz is sent to the subwoofer.
- 100 Hz – 4,000 Hz is sent to the woofer.
- 4,000 Hz – 20,000 Hz is sent to the tweeter.
When sending high amplitude audio signals from a powerful amplifier to a speaker crossover, out-of-band energy can “leak” into speakers that aren't expecting it.
This has the potential to cause the individual speakers to act non-linearly and cause distortion in the speaker's sound.
On top of all that, overloading the speaker with a high-amplitude audio signal can actually burn or melt the electrical components. If the speaker is not rated to handle certain levels of electricity, it may not be able to dissipate the heat energy caused by the audio signal.
This can result in the electrical lead wires and even the voice coil melting or burning. A damaged electrical connection or driver is not good. If the speaker performs at all, it will produce noticeable distortion.
To recap, though it is certainly possible to overload the mechanical and electrical components of a loudspeaker, it is typically amplifier clipping that causes our speakers to sound distorted.
Is Distortion Bad For Speakers?
As we've discussed, distortion in speakers is typically caused by the clipping of the audio signal going into the speakers.
Distortion itself will not cause damage to a speaker. However, the factors causing the distortion can also cause serious damage to the speaker.
So typically, a bit of distortion will not harm a speaker. Rather, it will just sound bad. We can think of audible distortion as a warning sign that damage could be occurring, even though it is not necessarily occurring.
It's still best practice to turn a speaker down when it's distorting.
As discussed in the previous section, the speaker damage can be caused by too much voltage or current (too strong of an audio signal) being applied to the speaker driver.
This may result in mechanical damage to the driver, but if damage is to be done, it's generally going to be the melting, burning and deformation of the voice coil.
As the electrical audio signal passes through the voice coil, the driver produces a coinciding sound. The inefficiencies inherent to any transducer produce heat in the system. If the speaker cannot dissipate the amount of heat generated, the voice coil can become damaged.
As we'd expect, the greater the audio signal's amplitude, the more heat is created in the voice coil.
So if the amplifier is too strong for a speaker, it could potentially send a signal that is “too hot to handle” and damage the coil.
Of course, if we keep the volume down, a stronger amp should work just fine with a smaller speaker.
It is also possible for a weaker amplifier to damage a speaker that is, on paper, capable of handling its output.
This is an extreme case that would require significant overloading at the amplifier level. If we were to apply enough gain to the amplifier that the signal became more of a square wave, we could end up sending enough electricity to the speaker to damage its voice coil.
However, there would be significant distortion before this would happen. It may even be impossible if the speaker can handle more than the absolute maximum output from the weaker amplifier.
Active Vs. Passive Speakers
In theory, it's more likely that a passive speaker will produce a distorted output and sustain damage than an active speaker.
Active speakers are built with internal amplifiers. When properly designed, a built-in amp and crossover network should be ideal for the speaker drivers they drive.
Passive speakers, on the other hand, rely on external amplifiers. It is, therefore, up to the user to properly match the active amplifier to the passive speaker. There is a greater potential for improperly matched amps and speakers to distort and even get damaged.
That is not to say that passive speakers are inherently more fragile than active speakers (plenty of arguments suggest the opposite). It's simply a point I thought was worth mentioning in this article.
Can You Fix A Distorted Speaker?
The easiest fix for a distorted speaker is to turn down the volume.
If the original audio signal has embedded distortion, then there's nothing we can really do to stop the speakers from sounding distorted except for changing the song/audio.
Speakers can also sound distorted if they are damaged. Fixing the distortion in a damaged speaker means repairing the damaged speaker.
A speaker can sustain mechanical damage to its cone, speaker or surround if it is forced to move further than it was designed to.
A speaker can also sustain thermal failure when too much electrical power is sent to the electrical components (voice coil, electrical lead wires and even crossover networks). Amplifying the signal (turning up the volume) can actually cause the internal components to melt or burn as they fail to dissipate heat.
Of course, speakers can also sustain tears and deformities from physical impact. This has more to do with the physical handling of the speakers.
Repairs must be made to fix the damage, rid of the distortion, and have your speaker sound great like it once did.
- Replacing a melted/burned voice coil.
- Replacing the electrical lead wires.
- Fixing the crossover network.
What causes audio distortion? Audio distortion is caused by any non-linear behaviour of electronic components and by power supply limitations. Specific causes of audio distortion include:
- EQ, frequency response and crossover networks (linear distortion).
- Overloading electrical components especially amplifiers (non-linear saturation distortion).
- Trying to surpass the maximum digital headroom (digital clipping distortion).
How do you fix a rattling subwoofer? The rattling of a subwoofer is typically a result of loose objects in or around the speaker enclosure. To fix a rattling subwoofer, try the following:
- Reposition the subwoofer.
- Remove any objects that are touching the subwoofer enclosure.
- Tighten any screws that hold the enclosure together (this includes the grille and the feet of the woofer, if applicable).
- Secure the wires within the subwoofer.
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.