Function of Voice Coils in Speakers. Why Do Voice-Coils Burn Out?

Speakers are devices used to reproduce sound. Speakers receive sound signals in the form of electric signals and convert the signals into the corresponding sound. There’re many types of speakers available today. They differ in size, shape, frequency response range, and power handling among other features. Regardless of these differences, speakers have several components that all work together to reproduce sound. The most important components of speakers include the magnet, cone, surround, suspension, and voice coil among others. Today, we will discuss the function of voice coils in speakers, why voice coils burn out, and how to prevent them from burning out.

What’s a Voice Coil and what are its Functions?

A voice coil, just like the name suggests, comprises of a coiled wire connected to the speaker driver terminals. It receives electric current from a source and converts it into linear motion. Basically, a voice coil functions as an electromagnet. The coiled wire is typically made of aluminum or copper material. The wire is coiled around a magnetic metal.

Once electric current is conducted through the coiled wire, a magnetic field is produced around the coil. Consequently, the electromagnetic field magnetizes the metal on which the coil is wrapped. This creates south and north polarities. As such, an electromagnet is created, whereby the polarities are switched by reversing the flow of electric current.

Speaker voice coils work by using the principle of electromagnets to reverse the flow of electric current repeatedly. The signal from the source (such as an amplifier) switches the electric current repeatedly such that the polarities switch between the negative and positive electric charges. The electromagnetic field of a voice coil usually sits inside a permanent magnetic field. The permanent magnetic field is created by the magnet you see on a speaker. The two magnetic fields interact whenever the polarities of the electromagnet are switched.

As the polarities get switched repeatedly, the two magnets are attracted and repelled repeatedly. As such, the coil moves back and forth. The movement of the coil is what moves the speaker cone back and forth. As the speaker cone moves, it vibrates and moves the air in front of it, thereby creating sound waves.

To understand the working principle of a voice coil better, think about what happens when two magnets are placed closely together. As you place two magnets closely together, they attract each other forcefully when the polarities facing them are opposite. The magnets repel each other forcefully when the polarities facing them are similar. This is how a speaker coil works when polarities are switched.

Does the Size of a Voice Coil Matter?

Voice coils come in various sizes in terms of length and diameter. To start with, the length of a voice coil determines the distance that the coil will move back and forth. For instance, the voice coil needs to move a longer distance when reproducing low frequencies and when being fed with a lot of power. The coil may be lengthy on a thin pole plate or short on a thick pole plate to give the same results. The coil only needs to move a short length when reproducing high and mid frequencies.

A small coil has less power on a speaker cone whereas a larger coil has more power on the speaker cone so long as the diameters of the speakers in comparison are the same. If the coil is small, then it becomes more resonant than a larger coil so long as the cone diameter is the same. Although some smaller coils appear more efficient, the efficiency is only experienced when hitting a certain resonant low frequency. If the frequency is above that resonant low frequency, then the speaker will have lower efficiency when compared to a speaker of the same cone size but with a larger coil.

A larger coil usually has more control on the speaker cone. Thus, the larger the coil, the better the linearity and damping of the cone. However, making large coils is quite expensive. Larger coils also make it more challenging to assemble a speaker. Also, a larger voice coil demands a larger magnet. Nevertheless, larger coils result in better power-handling.

Why Do Voice Coils Burn Out?

If the voice coil melts or burns out, then it’s most likely that it has experienced an electrical surge. You can tell that a coil is melting or has burnt out by detecting a burning smell from the speaker. You can also tell that the coil has burnt out by hearing a crunchy noise upon pressing the cone inward. Here’re some of the reasons why voice coils burn out:

i. Overpowering the speaker

If you’re using an extremely powerful amplifier beyond what the speaker can handle, you’ll most likely burn out the coil. This will likely happen when the volume is raised to a high level. If the amplifier has a power rating that is double or thrice that of the speaker, then the coil may burn out at higher volume levels.

ii. Under-powering the speaker

Another common reason why voice coils burn out is under-powering the speaker. If you feed the speaker with a weak signal, the speaker will clip and distort, especially when you struggle to increase the volume level. Consequently, the voice coil may burn out.

iii.A malfunctioned amplifier

A malfunctioning amplifier may destabilize the signals being sent to the voice coil, thereby burning it out.

iv.Poor speaker cable contact

In the event that the positive and negatives terminals of a speaker cable have poor contact on the speaker, there will be some noise. As a result, distortion may be experienced and the voice coil may burn out.

v. User error

Besides the aforementioned problems, issues related to user error can also make the coil burn out. For instance, raising the volume level excessively for a prolonged period can burn out the coil. Also, using treble and bass correctors excessively may burn the speaker coil. If you set the correctors to their maximum, the power emitted may be thrice or more, thereby burning out the coil. Setting up the equalizer improperly may result in clipping, and this can burn the coil.

How to Prevent the Voice Coil from Burning Out

The best way to prevent the voice coil from burning out is using an amplifier with the right power rating. The amplifier should neither under-power nor overpower the speaker. You should also avoid turning the volume level and bass boost all the way up. Also, use the equalizer appropriately.

How to Fix Speaker Other Voice Coil Problems

Besides the coil burning out, there’re other problems that voice coils experience. Sometimes, it’s possible to fix these issues. Basically, it’s easier to repair issues affecting larger coils than smaller ones. Here’re some coil problems and how to fix them:

i. The coil is off center

Although voice coils in most modern speakers hardly go off center, it may still happen. In most cases, the coil goes off center as a result of moisture on the cone. You’ll start noticing the problem when the speaker makes grating noises when it’s being used. You can fix this problem by moving the cone to the center. To do this, hold the cone gently and ease it back to the center. Doing so will move the cone back to position. Be careful when handling paper cones as they tear easily.

ii. The coil is misaligned

Some speakers come with a spider that holds the speaker coil in place. If the spider is not properly aligned, the coil won’t be in place such that it may rub against the magnet. You can fix this problem by aligning the spider properly. To do this, find a screw at the center that keeps the spider in place. Tighten the screw to align the spider properly, thereby aligning the coil in place. Avoid over-tightening the spider as it will misalign the coil further.

iii.The coil detaches from the cone

Another common issue with voice coils is that they can get detached from the speaker cone. This usually happens as a result of overheating or aging. Overheating and aging destroys the glue holding the coil onto the cone, making the coil detach from the cone. You can fix this problem by re-gluing the coil onto the cone.

Replacing a Voice Coil

Some voice coil problems might be irreparable. For instance, if the voice coil burns out, you’d have to replace it. To replace the coil, get an exact coil as the original one for a perfect fit. Some manufacturers offer replacement coils. A replacement coil will come with installation instructions. You’ll need to disassemble the magnet to remove the burnt coil. Then glue the replacement coil in place. Ensure the replacement coil is properly aligned in place. Be careful during the entire installation process, including when disassembling and reassembling the speaker components.

Conclusion

The voice coil is like the heart of a loudspeaker. It pushes and pulls the cone according to the respective electric current to allow the cone to reproduce the corresponding sound. It’s important to take good care of the voice coil to prevent it from burning out. In case of a burnt voice coil, replace it for the speaker to regain its functionality.

David M Foster
 

David M Foster is an award-winning sound engineer with over 13 years in the sound industry. He now works as a freelance sound engineer. He uses his insider knowledge and vast experience of the industry to shed more light on sound systems. He is a family man and the head content at Speakerchampion. Learn more about us.

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