The Components of a Subwoofer
A subwoofer is an electromechanical driver that converts electrical waves into mechanical vibrations which produce audible sound waves. Have you ever wondered what components make up a subwoofer and how they work together to produce bass? Or what materials and designs make one subwoofer better than another? This blog will explore the various components of a subwoofer, how each component works, and what materials are commonly used for each component.
The basket, sometimes called the frame, is the main body of the subwoofer that holds all of the components of the subwoofer together. Baskets are typically made out of plastic, aluminum, or steel. A “cast basket” is a basket that is made out of cast aluminum. Aluminum is more efficient than steel at drawing heating away from other components of the subwoofer. This can be attributed to the fact that cast aluminum baskets are usually thicker than stamped steel baskets are as well as the fact that aluminum is an ideal material for heat sinking. It is due to these qualities that cast aluminum baskets are more ideal than stamped steel for handling large amounts of current. Another advantage of cast aluminum baskets is their rigidity and associated ability to hold parts in alignment for longer. One of the main reasons a company will choose a stamped steel basket is cost. However, it is possible to have a well-designed stamped steel basket which often looks like a larger gauge of steel being used.
Another interesting part of baskets is the actual process used to make them. Tooling is the process of manufacturing components using machines and computer cutting programs. This process will determine output capacity, product lifecycle, quality, and pricing. There are two major types of tooling: proprietary and open. Open tooling typically is when the logo is ground off of a component, essentially a copy or “off the shelf” design. Proprietary tooling is unique from manufacturer to manufacturer and is what gives a company a distinct look and style. This is the reason why products produced with proprietary tooling are patented.
The surround is the flexible piece of the subwoofer that connects the basket to the cone and keeps the cone centered. Surrounds are typically made out of foam or rubber. What sets these materials apart is longevity; a rubber surround usually has a longer lifetime than a foam surround. Foam surrounds self-dampen, are light, and have minimal effects of the motion of the cone. Rubber surrounds generally last longer and are more durable. There are many different types of rubber surrounds including urethane, santoprene, and butyl. Urethane and butyl’s main advantage is flexibility and santoprene’s is a longer life span. There is not much of a cost difference between the two surround types and there are many other factors worth considering when choosing a subwoofer.
The cone, sometimes called the diaphragm, moves back and forth to displace air and create sound. The material used to create the cone impacts the shape of the cone and therefore, the sound as well. Common materials used to make cones include treated paper, polypropylene, kevlar, aluminum and magnesium, and carbon fiber. Treated paper is one of the most common materials used to make cones. It offers advantages like being so lightweight it yields the fastest response time. What makes the paper “treated” is a coating of carbon fiber, polyglass, kevlar, or csx to give the cone durability. Polypropylene, another commonly used material in cones, is lightweight and more rigid than treated paper. Kevlar offers advantages such as lightweight, flexible, durable, strong, long lifespan, and better sound displacement. Aluminum and magnesium offer advantages such as rigidity and it can cause high pitch resonance and lower frequency. Carbon fiber, most similar to kevlar, is lightweight, flexible, durable, and can offer higher output levels.
The dust cap prevents dust from reaching the voice coil and magnetic gap of the subwoofer. The smallest piece of dust or debris contacting the voice coil or magnetic gap can create problems. Not only do they protect the voice coil and magnetic gap, but they can also add to or subtract from the driver’s sound. This can be attributed to the material used to make the dust cap. Common materials used in making dust caps include cloth, paper, felt, and aluminum. Each material has a different porosity and stiffness, affecting different frequency ranges based on these factors. Cloth doesn’t have much effect on the overall sound. Harder than cloth is paper, which can extend the higher frequencies. Felt mellows upper-mids and higher frequencies. Even stiffer than paper and felt is aluminum, which adds top-end extension. The disadvantage to aluminum is its weight, which can have the consequence of lowering SPL. The size of the dust cap determines where it attaches to the cone. This is important because different frequencies come from different areas on the cone. The shape affects the way that the subwoofer projects frequencies. Most subwoofers utilize a dome shape.
The spider is attached to the bottom of the cone and the top of the voice coil. It has many functions including controlling the movement of the cone, keeping the voice coil centered within the magnetic gap, and preventing particles from entering the voice coil and magnetic gap. The number of valleys and peaks (termed corrugations) in a spider affects the throw. Durability in the material is key in preventing spider sag and promoting consistent performance as well as longevity.
The tinsel leads connect to the speaker terminals. They can be above or in between the spiders. When tinsel leads are located in between the spiders they are termed “stitched”. Stitched tinsel leads prevent them from hitting the cone as it moves and making a noise. Another common term used when referring to tinsel leads is “direct”, which means that there is no terminal in between the speaker wire and tinsel leads.
The terminals are the positive and negative wire connections of a subwoofer. Spring terminals are most commonly used for ease of use.
The voice coil is tightly wound around a cylinder, called the former (or bobbin). It attaches to the cone and the spider and sits within the magnetic gap (the center of the motor). Electricity flows through the voice coil to create a magnetic field that pushes and pulls against the magnet. This force is what moves the cone and voice coil back and forth, creating mechanical vibrations and audible sound waves. There are different types of voice coils, determined by the location in which the top plate lines up with the voice coil. Changing the gauge, or size, of the voice coil wire changes the amount of power that the subwoofer can handle. Changing the material of the former can change the cooling efficiency of the voice coil. If the voice coil gets too hot, the wire can become burned or unwind. Copper is most commonly used for its ability to conduct current and withstand higher temperatures. Aluminum is also commonly used for its low mass (1/3 the weight of copper). The drawback of aluminum is that it is less conducive than copper. Other cooling features are often added, such as heatsinks or pole-piece vents, to prevent this from happening. An “overhung” design utilizes a top plate smaller than the length of the voice coil. This allows for greater Xmax and cooling. The drawback to this is more mass, making the suspension more difficult to move, and giving the subwoofer a lower sensitivity. An “underhung” design puts the entire voice coil below the top plate. This gives the coil less mass, making the suspension easier to move, and giving the subwoofer a higher sensitivity. The drawback to this is a limited range of motion and therefore less Xmax. It is also important to note that the voice coil has a constantly changing magnetic field based on the frequency sent to the subwoofer from the amplifier.
The magnet connects to the top plate and the back plate and provides a constant magnetic field. One misconception is that a bigger magnet inherently means a better subwoofer. Different kinds of magnets are used to suit different sizes and achieve different tone qualities. The two most commonly used magnets are neodymium and ferrite. Neodymium offers the greatest magnetic strength while remaining small and relatively light. The stronger the magnetic field, the better the frequency response. Ferrite weighs more than neodymium, but costs less, has a long magnetic lifespan at high temperatures, and can create a wide range of tones.
The top plate sits above the magnet and directs the magnetic flux to the gap around the voice coil. This works with the backplate to create a magnetic field.
The backplate, or t-yoke, is connected to the pole piece and is the opposing force. It also pulls heat away from the voice coil.
The pole piece directs the magnetic field produced by the magnet.