The S-Series speakers have a large voice coil. The 6.5-inch and 6x9-inch models have a 35-mm voice coil, and this large voice coil size increases their driving power and control of the motor. The S-Series speakers are the first in the industry to use a material called CFRP (Carbon Fiber Reinforced Plastic), a very lightweight yet rigid material. On a standard, off-the-shelf oval cone, the edges are naturally weaker than the center due to the elongated shape. Since the CFRP material is directional, it can be manipulated during the molding process to strengthen the areas of the cone that are normally weak. The result is rigidity throughout the cone that delivers accurate and efficient performance. The ability to manipulate the CFRP material during the molding process is currently exclusive to Alpine and the S-Series speakers. Alpine has three patent-pending procedures in support of this innovative manufacturing process.