How Does a Subwoofer Work?

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A few years back, people perceived subwoofers as rather special types of speakers that could only be afforded by high-profile music enthusiasts. However, this perception has changed in recent times where the subwoofer has become a necessity and the backbone of any home theater sound system.

The reason why this loudspeaker has become so common is due to its extremely complex and high-quality design that allows it to handle the low pitched frequencies such as the booms, the thunders, the explosions, and the rumbles that fall in frequencies ranging from 20Hz-100Hz.

But, regardless of how well it handles the low-pitched audio signals, the subwoofer cannot work on its own. It requires the help of the full-range speakers to take care of the high frequencies while it reproduces the deep juicy bass.

By working as a team, the sub will demand bigger cabinetry for efficiency while freeing the rest of the speakers by allowing them to demand smaller cabinetries since they won’t be demanded to reproduce any low frequencies. In this guide, I will educate audio enthusiasts about what a subwoofer is and how it works.

What is a Subwoofer?

best subwoofer feature imageBefore I explain how a subwoofer works, it’s important that you first understand what this special loudspeaker is. In simple terms, a subwoofer is a special type of speaker that emits sounds in the low end of any frequency range. In all cases, this speaker doesn’t come alone but rather comes as a combination with other woofers or rather full-range speakers.

Most music and movies today come with special dramatic effects that make the contents entertaining. Since most of these effects have different frequency ranges, having a combination of a subwoofer and several full-range speakers means that you won’t miss any sound regardless of whether it’s in the low end or the high end of a frequency range.

The reason why a subwoofer is so integral when it comes to reproducing deep punchy bass is due to its built that allows it to handle high sound pressure levels (SPLs). If you happen to task regular speakers to reproduce the low frequencies, they will either distort the deep bass or leave gaps when it comes to reproducing those low-frequency waves.

But, with a subwoofer, this speaker will create a cleaner sound texture by filling those low-frequency gaps in any soundscape coming from your audio system. With that said, I will now discuss how a subwoofer works. Since a sub is made up of two sub-systems—the suspension system and the motor system—I will discuss each system independently to see how it works.

How Does It Work?

subwoofer cross-section

Above is an image showing a simple cross-section of a subwoofer

To help you understand how a subwoofer works, I will discuss the main parts of a subwoofer and what each part is tasked to do. Later on, I will conclude by discussing passive and powered subwoofers as well as mention something about subwoofer enclosures.

So, How Does the Suspension System Work?

The Basket

The basket is actually the outer casing of the subwoofer that functions as the skeleton. Its main purpose is to hold the rest of the components in place while still providing structural support by being screwed to the cabinet with special bolts.

Since subwoofers generate a lot of heat, the basket is designed with special vents on the sides to allow the inner components to breathe. Its hollow design allows it to suspend the moving parts at the center to allow a precise to and fro movement when reproducing the low frequencies.

Surround

The next component is the surround. Made from either rubber or foam, the surround is a flexible circular piece that connects the cone/diaphragm to the basket. It also keeps the cone perfectly centered to prevent putting any stress on the voice coil.

The surround is a very special component. It’s designed to withstand heavy excursions when the cone is moving far forward and far backward when producing those punchy bass effects. Since it must retain its initial shape after being overworked, having a subwoofer with a surround made of a combination of synthetic materials is usually better as it can withstand the high excursions while lasting for a longer time.

Cone/Diaphragm

The cone is another part of the subwoofer that plays a very critical role. It’s usually centered in a linear position by the surround where it will vibrate the air to create sound. Since this part is usually the most important in a subwoofer, it must be designed carefully to avoid any design flaws.

And since the subwoofer is designed to handle low frequencies in high sound pressure levels where sound is played in high decibels, the cone needs to have a high level of rigidity as well as low mass. Therefore, it needs to be constructed from special materials such as plastic, organic fiber, or metal.

Dust Cap

The dust cap is usually a small piece attached at the center of the cone to protect it against dust. Depending on the quality of your subwoofer, the dust cap can either be protruding slightly from the center or bulging inwards into the cone.

Spider

Another crucial component that plays a very critical role in your subwoofer’s performance is the spider. Located just beneath the cone assembly, the spider is usually attached to the voice coil then extends out to connect to the basket. The reason why it’s called the spider is due to its corrugated design. To keep it strong, this component is made from a special fabric that has been treated with resin to stiffen it.

In a subwoofer, the spider plays two key roles. Its primary role is to monitor the upward and downward movement of the cone while keeping the voice coil centered within the magnetic gap. On the other hand, its secondary role is to prevent dust from penetrating inside the voice coil or inside the magnetic gap where the voice coil moves up and down.

Tinsel Leads

The last components that make up the suspension system are the tinsel leads. These are wires that run from the voice coil to the speaker lead ports. They’re usually flexible and very durable meaning they can’t be damaged by the extreme vibrations created by the diaphragm when the subwoofer is pumping out the bass.

How Does the Motor System Work?

The motor system is the backbone of the subwoofer as it’s the one that provides the force or rather the power that moves the components that make up the suspension system.

Voice Coil

At the heart of the subwoofer lies the voice coil. This component comprises of a thin copper wire wounded around a cylinder known as the former. When the amplifier sends audio signals to the subwoofer, electric current flows through the voice coil creating a magnetic field that pulls and pushes the voice coil against the magnetic gap.

By alternating this current, the voice coil moves upward and downward to produce sound. However, though I’ve mentioned that the subwoofer can handle low frequencies with ease, you need to understand that the thin copper wires wounded on the cylinder are held together using an adhesive. Since a subwoofer generates a lot of heat when performing at pick power, this extreme heat can overheat the adhesive causing the wires to unwind.

Magnet

The last component is the magnet. One myth most people believe in when it comes to magnets is that the bigger the magnet is, the better the quality of the subwoofer. Although this is true at some point, it’s not always the case as magnets are constructed with varying technologies that influence their sizes. The magnet doesn’t come alone either. It’s usually covered with a top and backplate that helps to direct the magnetic flux to the voice coil when a current is supplied.

Now that I’ve discussed the two subwoofer systems and how each of them works, my final step is to discuss passive and powered subwoofers as well as mention something about the different types of subwoofer closures.

Powered vs Passive Subwoofers

When learning about subwoofers, you’ll likely come across passive and powered subwoofers. Passive subwoofers on their side are powered by an external amplifier meaning their enclosures don’t have any preamps installed inside them. These types of subwoofers are usually powerful and require you to connect a very powerful amplifier between them and the receiver.

On the other hand, the powered subwoofer, also known as the active sub, comes with its own preamp that’s usually fitted inside the enclosure. Besides, it has a line-level crossover that does a decent work of allowing you to adjust the frequency range of the subwoofer and the main speakers.

Type of Cabinet Enclosure

Lastly, I will discuss the subwoofer enclosures. The reason why I’ve included the types of enclosures in my discussion is simply because enclosures impact the performance of a subwoofer in a massive way. With that said, let’s discuss the three main types of enclosures you’re likely to come across to.

Sealed Boxes

Just as its name suggests, a sealed box enclosure is one that doesn’t have an opening. By isolating the subwoofer’s back from the front, what happens is that clean, tight, and well-defined bass is manufactured.

Ported Box

A ported subwoofer cabinet, on the other hand, is one that contains a hole or rather a port. One good thing about these enclosures is that they amplify the output on certain frequencies to reproduce those low frequencies without ever damaging the subwoofer.

Isobaric Box

Isobaric enclosures are very unique types of boxes that allow you to mount two subwoofers inside a single box. Here, the enclosures are sealed and smaller in size allowing them to push tremendous power from both subwoofers to get the right output. When coupling your subwoofers using this technique, you can position the subwoofers in a cone to cone setup, cone to magnet, or magnet to magnet setups.

Conclusion

In conclusion, understanding how a subwoofer works is really important as it gives you an idea of what you’re supposed to look out for when making a purchase. In this guide, I’ve discussed each component in detail to help you understand their roles. In addition, I’ve discussed briefly regarding passive and powered subwoofers as well as the three different types of subwoofer enclosures.

 

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