 MBQUART - PWD304Subwoofer...  MBQUART - PWD304Subwoofer |  Diamond Audio shows the use...  Diamond Audio shows the use of multiple spiders. Note the distance between them. This will help the voice coil/cone assembly maintain linear movement at hight excursion. | |
SPIDER
Everyone familiar with a speaker has seen the flexible corrugated woven material that exists just below the cone. This is the spider, which is a part of the speaker that helps maintain linear movement of the voice coil. This maintains control over the entire cone movement. Spiders are generally made of cotton, poly-cotton blend, or conex. They also come in a variety of sizes. However, the major difference between spiders is the number of corrugations, meaning the valleys and peaks, and the heights of these. This is important because some speakers have longer throw than others. The wrong spec spider has the potential to break down quickly and create "spider sag." That can greatly affect the sound quality of your speaker.
There are two different styles of spiders. The first is the cup spider. This is generally found on less expensive woofers. A cup spider has sidewalls that are used to give greater depth so that the neck of the cone does not hit the top plate of the speaker under high power. The second is the flat spider, which is used in more expensive/high excursion woofers where every part is designed to fit appropriately. These are inclined to have a more linear movement along with a greater life expectancy.
VOICE COIL
The voice coil is possibly the most important piece of a subwoofer. This is the tightly wound spool of wire which makes up the secondary part of the motor structure in a speaker. It is physically attached to the cone and spider of the speaker and is submerged in the magnetic gap in the center of the motor structure. When power, AC voltage, is supplied the coil creates an alternating magnetic field that pushes or pulls the coil in and out of the magnetic gap. This movement translates into acoustical energy.
A voice coil is made of two main parts; a former (bobin) and a coil: 1) Formers come in a variety of materials for a variety of applications. Some of the more common are mylar, aluminum, or fiberglass. The former is the physical form that holds the voice coil and attaches to the spider and cone of the speaker. 2) Coils create the alternating field within the motor structure. The wire gauge of the voice coil is crucial for determining the power handling of a subwoofer. Wire used for coils comes in three materials: copper, aluminum, and CCA (copper clad aluminum). Equally important is the preparation and curing of the glue used to bond the coil together as well as to the former. Poor glue usage may result in the coil falling off the former, leaving you stranded without bass.
TOP PLATE
Directly mounted to the underside of the basket is the top plate. This is generally screwed to the basket or staked on using a high power press. The top plate sits above the magnet and directs magnetic flux to the "gap" where the voice coil resides. This works directly with the t-yoke to create a magnetic field. In turn, this magnetic field reacts with the alternating field produced by the voice coil, consequently moving the voice coil forward and back within the gap.
Steel is the only material used for top plates. These are generally of the low carbon variety, for carbon acts as a speed bump for magnetic energy. High carbon content can greatly reduce the amount of force provided by the magnet, and quickly saturates the top plate. Luckily, low carbon steel is cheaper and considerably reduces the cost of producing subwoofers.
 Studio Model 3124SVC Woof...  Studio Model 3124SVC Woofer |  A hexagon subwoofer that mounts...  A hexagon subwoofer that mounts in a round hole? Only if you're Xtant. | |
MAGNET
The life force of the speaker. This is generally the part that most everyone judges a speaker by. This is understandable. To most individuals, the larger the magnet, the better the speaker. Unfortunately, that is not always the truth. But what is the magnet to a subwoofer? This is the object between the back plate and t-yoke that provides the counter force to the voice coil. Generally a ferrous material that, like iron, retains a magnetic field constantly. These magnetic fields are referred to as flux lines. Using metal plates, the top plate and the t-yoke, the magnetic fields can be controlled and concentrated to another area, in this case the voice coil gap.
T-YOKE
Take the back plate of the motor structure and the pole piece that extends up to the center of the voice coil. The combination of these two is referred to as the t-yoke which provides a method of focusing the opposing force of the magnet back up to the location of the top plate. This opposing force creates a magnetic field with the top plate that is used to create a reaction with the alternating field created by the voice coil. As with the top plate, the t-yoke uses a low carbon steel structure. This steel structure in many cases serves another purpose: Ventilation. By boring a hole through the pole piece, air is then moved back and forth to effectively cool the voice coil. As well, the pole piece of the t-yoke also pulls heat from the voice coil, acting as a heatsink. Both can have a tremendous effect on power handling of the woofer. And today's speakers employ various forms of trickery to further improve the ventilation. Check out these speaker cutaways for these fine cooling techniques.
 No. this is not an alien robot....  No. this is not an alien robot. The Alumapro displays ingenuity with a cone and voice coil that can be replaced in minutes. |  Bazooka brings us the liquid...  Bazooka brings us the liquid cooled subwoofer. What's next? A turbo and intercooler? | |