Complete Guide To Understanding How Subwoofers Work

Manufacturers often market their subwoofers by touting the design of their product by saying it’s the best.  Unfortunately, most of the time, that information just goes unnoticed. If you don’t understand all of the components, how they function and how they work together, you’re not going to understand why a particular model is the best.  This article is meant to educate car audio enthusiasts so they make a more informed decision when choosing a subwoofer to buy.

What is a subwoofer?

A subwoofer is a special type of speaker that emits sound on the low end of the frequency range, more commonly known as bass.  Normal speakers produce a wide range of frequencies, but don’t reach the lowest ones. The subwoofer helps to create a cleaner sound texture by filling in this low-range gap in the soundscape coming from your system.  Without a subwoofer, regular speakers either distort deep bass or simply don’t deliver it.

Each subwoofer  is made up of two sub-systems: the suspension system and the motor system.  Let’s start by looking at the suspension system.

How the suspension system works

For a subwoofer to push out sound, it requires a back and forth movement of its central assemblage.  Think of this as the air-moving system in the subwoofer that physically creates the bass you hear.

Basket

The basket functions as a skeleton or outer body.  It holds all of the other components in place with bolts and other smaller support pieces, but suspends those moving components in the center.  In that way, it is designed so that all of the vibration produced when the subwoofer is working doesn’t actually cause the entire system to rattle. 

It also includes venting around the sides to allow air to cool the inner parts.  Subwoofers actually create a lot of heat, so a well designed system prevents overheating when used for extended amounts of time.  Speaker leads (where you connect the wires) will also be found on the outside of the basket, too.

Finally, the basket will include a number of screw holes on the front end, which allow it to be securely fixed into a subwoofer box.

Surround

The surround is a flexible, circular piece that connects the basket to the cone and keeps it centered. If the cone isn’t kept perfectly centered and linear when it moves, it can place stress on the voice coil.  It also acts to restore the voice coil to its resting (“neutral”) position.  

Two materials are commonly used for a surround: foam and rubber.  

One of the benefits of foam includes the ability to withstand heavy excursion (how far the cone moves from its resting state).  Foam naturally returns to its neutral position when not in use and doesn’t warp with use over time. Furthermore, it is super lightweight and is often combined with other materials to improve strength and durability. 

Although rubber is typically more durable than foam, it may have a tendency to warp after lots of heavy use or with more excursion.  As a solution, rubber in surrounds is also treated and combined with other synthetic materials to improve its qualities and ability to last.

Cone (a.k.a. Diaphragm)

This piece in the center of the surround is what vibrates air, creating sound.  It is extremely important to the overall sound quality of the subwoofer, so it must be designed very specifically.

The cone requires a certain level of rigidity as well as a low mass.  The material of the cone is made of either plastic, metal or from a special type of paper composed of wood and organic fibers.  High flexibility allows for a good production of bass sounds by subwoofers.

Dust Cap

This is the piece at the center of the cone.  Like the name suggests, this cap is meant to protect the voice coil from dust.  Some dust caps are designed to protrude slightly from the center of the surround. Other modern designs actually extend inward like the cone.

Spider

At the bottom of the cone is the spider.  It is positioned around and attached to the voice coil and extends out to connect with the basket.  It gets its name from its round, corrugated design and is made from fabric treated with a resin to stiffen it.

The spider controls the up and down movement of the cone assembly and keeps the coil centered within the magnetic gap.  A secondary purpose is to prevent dust and any other outside particles from getting to the coil inside the subwoofer. Some modern subwoofers have two spiders for a stronger and more controlled hold on the central assemblage.

Tinsel Leads

Tinsel leads deliver the signal.  These are the two wires that connect the speaker lead ports to the voice coil in the center of the subwoofer.  They are very flexible and durable wires as they will endure a lot of vibration when the subwoofer is pumping out bass.  If two spiders are used in a subwoofer, these tinsel leads will often be positioned between the two spiders.

How the motor system works

This system is the heart behind the subwoofer.  It provides the force that moves the components making up the suspension system.

Voice Coil

One of the most important parts of the subwoofer, a voice coil is attached to the bottom of the cone.  It consists of two parts: a wire and a cylinder (a.k.a. the former). The copper wire is wrapped around the cylinder located in the center of the subwoofer.  When electricity flows through the voice coil, it produces a magnetic field that pushes and pulls against the magnet. By alternating the current, the coil and cone move back and forth, producing sound. 

That current comes from the signal sent to the subwoofer by an amplifier and the magnetic field is constantly changing based on the frequency of the signal.

Finally, the wire and cylinder are held together with adhesive, so it’s vital that it doesn’t get too hot. Otherwise, the overheated adhesive could be damaged and the wire could start to unwind.  

Magnet

Some people judge the worth of a subwoofer entirely on the size of the magnet, but this isn’t a good way to think.  Magnet design technology varies, just like the size. It is held in place by being connected to the top plate and the back plate.  

Top Plate

This metal piece next to the magnet helps direct magnetic flux to the voice coil.  If an alternating current is run through this, it will drive the center assemble to move.

Black Plate

This piece is located at the back end of the subwoofer.  Like the Top plate, it’s function is to direct the magnetic flux into the voice coil, too.

Frequently Asked Questions

How are powered and passive subwoofers different?

The difference is where the power to operate the subwoofer comes from. A passive subwoofer must be connected to its own power supply or external amplifier in order to be used, but a powered subwoofer has its own optimally matched amplifier built right into the system.  This means that a powered subwoofer can be connected directly to a head unit without an extra amp needed in the car.

These days, all encased subwoofers you see for sale (the kind that come in a cubic enclosure) are going to be powered.  If you build your own system, you can opt to buy a subwoofer and amp separately and connect them later. 

How do you know if a subwoofer is blown?

It’s easy to tell by when this has happened just by noticing a poor sound quality with “cracks”, rather than smooth, clean bass. 

Subwoofers and speakers “blow out” when too much power has been sent to the suspension system.  Every subwoofer is designed with a maximum amount of power. If that level is exceeded, it causes undue stress on the cone as it is moving up and down. If this happens for too long, it will tear or be separated from the surround.  This results is a distorted sound as the air is vibrated against an unsealed section of the cone. Blowing the subwoofer will also void the warranty if you have one.

If you check the cone, you may notice an actual tear in the material.  If it isn’t immediately apparent, the tear could be very small or be right along the edge of the cone. You can check for non apparent breaks by grabbing the edges of the basket using your thumbs to lightly press on the cone for a tear.

Can I use a subwoofer as a normal speaker?

No. There is usually a limit on the upper end of a subwoofer’s frequency range of 200 Hz. Loud speakers are able to produce frequencies above the abilities of human hearing, but subwoofers are only designed to deliver only the lowest frequency. It’s possible to extend a subwoofer’s upper frequency limit.  However, the modifications in the design needed to do this means its lower frequency limit would suffer. Better to leave the sound over 200 Hz to other types of speakers.

How do I tune the subwoofer for the best performance?

Tuning your subwoofer system is a skill every owner should know how to do.  This will help maximize the quality and clarity of your lowest frequencies.

The seven steps in car audio system tuning with a subwoofer are:

  1. Turn the subwoofer amp’s gain all the way down, the low-pass filter all the way up, and the bass boost off.
  2. Turn on the head unit and set all tone controls to their middle settings.
  3. Play a piece of music you know well which includes high, mid-range, and bass notes.
  4. Adjust the volume on the head unit between 25 percent and 75 percent of its maximum.
  5. Gradually turn up the gain on the amplifier until you begin to hear distortion (“clipping”)
  6. Turn down off the gain until the distortion stops.
  7. Slowly lower the low-pass filter until you can’t hear any mid- and high-frequency sounds, (such as those from guitars and vocals) coming out of  the subwoofer.

Remember to adjust each component in your sound system separately to get the best result.

Where is the best place to put a subwoofer in a vehicle?

The location of your subwoofer can make a big difference in how you experience bass in your car audio system.  But there are other advantages and disadvantages based on location that will be discussed. There are two choices: the cab or the trunk.

The Trunk

Car with its trunk open with two subwoofers showing how subwoofers work

First of all, the sub will be hidden and  out of the way, so you and the people in your car will have more space for yourselves.  On top of that, because it’s hidden, burglars won’t be tempted to steal something they don’t know is there, so it’s also safer in the trunk, too.  A final positive aspect of putting it in the trunk is that it’ll be secure in terms of stability when the car is moving. Trunk subwoofers are fastened behind the rear seats or tucked into a corner.

On the other hand, because it’s in the trunk, there’ll be less space for groceries, work gear, sports equipment, etc. that is better suited for that space. And just because it’s in the trunk doesn’t mean it’s totally safe from other physical contact.  If you put other stuff in the trunk, it’s possible for that to knock into the subwoofer as well. Corners taken too sharply or sudden braking could shift whatever is back there into your audio equipment.  

Finally, it’s not the easiest place to work when it comes to installing a piece of hardware.  The trunk can be cramped or difficult to understand how to secure something into. Maybe having a professional install the subwoofer into the trunk is a better option.

The Cab

interior of a vehicle with riders enjoying how subwoofers work

Although less common, others swear the sub belongs in up front.  They argue that it makes for a better sounding bass since there is no barrier between the audio and the listener.  Because of that, the bass range is wider and the sound is clearer. So if the quality of the bass is most important, install your sub in the cab.  They are also easier to install because there’s more space to work in. The downside to this is that it’s possible for the bass to be too “in-your-face”, which can be overwhelming for passengers ,especially those in the back seats.

Another drawback to consider is that it’ll be in clear view for potential thieves to target if your  car is in such a situation. 

What is the difference between a woofer and a subwoofer?

Sometimes people refer to subwoofers as just “woofers”.  But the words actually refer to two different types of speakers.  The key differences are frequency range and size.

A woofer is technically just another type of speaker made to produce frequencies from low to mid ranges.  A normal range for a woofer is about 20 Hz to 2,000 Hz. They are typically smaller than subwoofers.

Subwoofers are larger because they must move more air at a lower frequency in order to be effective.  They start at about 20 Hz but only peak at 200 Hz.

Final Thoughts

It’s important to understand how each part of a subwoofer works and it’s function in the bass system as a whole.  This will help you make a better decision when looking through the details of each product before buying.  Now, when you read about a special feature of a manufacturer’s product, it should make more sense what they are referring too.

Good luck in the purchase of your subwoofer!