Electricity is all around us, and even inside us. The presence of electricity has really skyrocketed in the past century, however, with the development of electronics. Today, our homes and communities are saturated with electrical devices.

Some of these devices were designed to make various types of noises, such as TVs and radios. Others make noises as a byproduct, such as motors in cars or electric tools. Some devices, however, are not designed to make any noise at all, yet many people find that they can still hear them hum. Examples of this include lightbulbs, televisions while the sound is off, toasters, and more.

That constant hum from these devices is usually drowned out by the other noises that are present in the environment, but late at night, when everything is quiet, many people can hear that buzzing. Some people find it comforting as a type of white noise, and others find it infuriating and annoying. Whether you love it or hate it, understanding that the noise isn’t actually the sound of electricity is important.

To understand where that noise is coming from, you need to know how modern electrical systems work. They operate using alternating currents (AC), which simply means that the electrical current alternates the direction that it is traveling at regular intervals, which are determined by the power plants that generate the currents. In the US, the current changes direction around 60 times per second, so the electricity is said to be 60 Hz (hertz).

The hum that people hear from electrical devices is a noise that is heard at twice that number, so in the US, the hum is measured at around 120 Hz. That hum, however, is not from the electricity itself, which makes no noise at all.

Instead, the hum is usually generated by a magnetic element within the electronic device. When you hear the noise near large electrical lines, it will usually be coming from the transformer, which is the piece of equipment that takes the high-voltage levels that come from the power plant and reduces them to a level that is safe to enter a home or business. This voltage reduction is essential for making sure that electronics aren’t overloaded when used. When the current passes through that transformer, it creates a slight hum.

Most electronics will also have a very small transformer within them that limits the voltage that can pass through, helping them to operate more reliably and safely. Once again, if the current is passing through them at 60 Hz, the hum from that internal transformer will be at 120 Hz. Most of the time, you will hardly be able to hear it.

The hum is normal and not something to worry about. If the hum suddenly gets louder, however, it could be a sign that the transformer is going bad, which could cause the device to stop working, or worse, a fire hazard, so it should be investigated.

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