Speakers are one of the few audio components that have made little advancement over the past decade. Until recently, that is. Power handling was not a prevailing issue for speaker manufacturers five years ago, but with the advancements in amplifier design, big power is cheap! This is forcing today's speaker manufacturers to come up with new solutions to build high power subwoofers that actually perform. The result has created a new movement with a massive onset of high excursion, high power handling subwoofers hitting the market -- and the competition is getting fierce.
So in what way is the evolution of speaker technology advancing? Simply put, just about every component of the subwoofer has been improved. We're talking sophisticated new cones, baskets, surrounds, and temperature management systems. The purpose of this article is to break down the subwoofer, part by part, to show the functions of each, and how they have changed for the better (or simply changed). For historical perspective Mike Klasco gives us a brief overview of the making of the modern long throw subwoofer.
GASKET
The front gasket found on most subwoofers today is simply a decorative piece. However, this gasket originally served to seal the woofer tightly to the baffle it was mounted to. Many manufacturers of home and pro audio product of years past would back mount the woofer to the baffle; hence the need for the gasket to be mounted to the front of the speaker. Back in those days, the gasket was usually made of pressed paper or cork. Some modern subwoofers still use those materials, but most are using foam rubber, plastic, cast rubber, and even cast metals. Engraved logos and laser etching have been accepted on the fascia as these gaskets have become a purely cosmetic marketing piece.
SURROUND (edge)
Surrounds come in many different types of materials. Some of the more common are Butyl rubber, Santoprene, EPDM, and compressed foam. Even though technology is constantly improving, not one of these materials really stands out above the rest as far as functionality. It may be true that the rubbers and plastic-based surrounds have better resistance to the elements, but pressed foam is lighter in weight and maintains its composure in heat and cold. So there are trade-offs to each of these materials.
The main purpose of the surround is to hold the top or outer portion of the cone linear during movement. However, many companies use the surround as a means of breaking or stopping the cone from moving beyond a certain point. This will effectively keep the voice coil within the magnetic gap (if designed correctly) and lower the wear and tear on the spider (also, if designed correctly). The trade-off generally comes in the form of a slightly higher distortion at high volumes; and with foam, a greater wear factor. For the most part, the oversized surrounds on woofers today are purely a marketing tool, and do not necessarily indicate the excursion capabilities of the woofer.
 Pioneer displays the use of...  Pioneer displays the use of the VCCS, a voice coil cooling system that uses a heatsink at the front of the cone. Another cool feature are the metal inserts on the cone for added strength. |  The Thunder series subs fromMTX...  The Thunder series subs fromMTX use a thermal-molded dustcap and ribbed cones formaximum rigidity. | |
DUST CAP
Purpose-built, purpose-named. The dust cap resides in the center of many speakers and is glued to or just over the voice coil. This keeps foreign particles, or dust, from entering the magnetic gap where the voice coil resides; these particles could disrupt the movement of the cone and/or damage the coil. Often these come in different shapes and sizes, some embossed with logos, some silk-screened with the logos and many with both. The dust cap as well as the cone come in a variety of materials; and often the former is made to match the latter.
The shape of the dust cap can affect the sound of the speaker, though this is more apparent in mid-bass and mid-range drivers. As for subwoofers, it is more about the strength of the material used for the dust cap. But different shapes can add more strength, too. By building in strength to the dust cap, this may also increase the rigidity of the cone once they are bonded together, all in all, reducing cone flex and the potential of cone breakup.
CONE
Ahhh, the cone. Generally shaped like a high volume funnel, this part attaches to the surround and the voice coil/spider joint. This is the part of the woofer that the voice coil moves forward and back to excite the air and produce sound waves. This forward and back movement is why the cone is often referred to as a "piston." As you can imagine, this is one of the most significant aspects of the subwoofer.
Very important to the cone are its strength and rigidity. Equally important is the weight and the shape of the cone. A proper balance of these items is key to a good sounding woofer that is flexible and works well in multiple applications. Picking the correct material becomes absolutely crucial at this point. Build materials range from the ever popular polypropylene and paper down to the composites such as carbon fiber, glass fiber, and Kevlar.
 Kicker's new L7 subs are truly...  Kicker's new L7 subs are truly unique, being the only square subwoofer in car audio. Note the solid cone that eliminates the need for a dust cap. | 
Stroker Cerwin-Vega! | |
BASKET
Made from stamped steel, cast aluminum, and even plastic composites, the basket or frame as it is commonly called, is the infrastructure that holds the speaker together. Generally speaking, all of the other components of a loudspeaker rely on the basket in one way or another. In the end, a speaker without the basket is just a bunch of parts.
As with materials, speaker baskets come in a variety of shapes and sizes. As the designs become more radical, so do the innovative features, such as integrated terminal mounts and heatsinks.
Strength is of the utmost importance since subwoofers of today are capable of tremendous SPL. High SPL relates to intense movement of a speaker cone. As the cone moves it creates resonance throughout the speaker, and this resonance can lead to cancellation. By adding strength to the basket, the amount of resonance can be greatly reduced, all the while improving the SPL, and the sound quality of the speaker.
TERMINAL AND TINSEL LEADS
Terminals come in a variety of styles. Some of the more common are the push terminal, binding post, set screw, and the standard tabs that coincide with female speaker disconnects. These terminals are where the speaker wire of an amplifier connect to the speaker to bring it to life.
Tinsel leads are the thin, flexible wire generally suspended under the cone. Think of these as the liaison between the terminals and the voice coil. These wires are made of multiple strands of alloys woven together with high strength fibers. This combination of materials provides extreme flexibility and greatly reduces any breakdown of the alloy's materials over time.