One of the debates of the decades has been between metal and paper or various exotic films. Each has its own strengths and each manufacturer has its own preferences. Let's talk about the basic functions of a loudspeaker and how cones should work, and what actually happens in the "real world".
"The material used to make the "perfect" loudspeaker cone must be as hard as steel, as light as a feather and able to open and close instantly. Unfortunately, there is no such thing as a perfect driver in the real world, so loudspeaker designers choose materials that are as close to ideal as possible.
The great advantage of plastic (polypropylene) cones is that they perform quite well and are very stable and cheap to produce. One of the great advantages of these films is that they have high damping and high loss. This means that they can have controlled cut-off points, resulting in a smoother drift at high frequencies. Some people believe that plastic films tend to sound smaller or more vivid than hard paper films. This is due to the near-capacitive recording effect inherent in floppy disk drives. However, if designed well, a good, well-damped plastic diaphragm can perform well in the midrange at a fraction of the cost of building a high quality paper diaphragm driver. All these advantages are available in paper, but paper diaphragms absorb moisture from the air, changing the quality and damping characteristics. Cost, manufacturing complexity, uniformity issues, performance and more make the choice of cone material a very difficult aspect of loudspeaker design. Paper cones made partly from felt and wool offer rigidity, low mass and inherent material loss, and usually provide the best sound from the cone. Sometimes rubber can be added to the paper to increase its strength. Speakers must vibrate at very high speeds (in the 20kHz range) and are usually made of metal, such as aluminium, titanium or silk. They must be very stiff but light in weight. Mid and bass drivers are usually made of exotic materials such as paper (with additives), Kevlar, ceramic or wood. All these different materials are chosen by the designer in order to achieve a difficult goal: the "ideal" loudspeaker. To be honest, these variables give the consumer a wide range of choices and keep us away from boring speakers of the same style.
