Citation :
There are often discussions about what kind of cone material sounds the best. There is no single answer for this and everyone has an opinion. One thing for sure however is that a type of cone can be classified by it's stiffness and internal damping. When sorted by these attributes, there is a wide variety of cone materials with polypropylene on the soft end and magnesium or aluminum on the hard end.
Top end frequency response of soft cones roll off smoothly and hard cones have breakup nodes. No debate about that. Poly cones actually do have breakup nodes but they are damped into non-existance. Many manufacturers use composite cones to reach a specific combination of stiffness and internal damping. Focal W-cones, Peerless sandwich cones, Vifa wood pulp, and even poly coated paper fall into the composite category. These manufacturers are trying to reach a happy medium.
Time for the truth telling. Any kind of internal damping robs detail from the original sound. If you were to compare a high resolution waveform reproduced through a soft poly cone with the original waveform, you'll see that the waveform has been smoothed out slightly. Peaks are rounded off and information is lost or distorted as energy is stored and released. This is even more visible higher in frequency where the driver starts to have a steeper natural rolloff. Do the same thing for a metal cone anywhere under it's breakup node and you will find the reproduced waveform closer to the original. That statement makes metal cones sound vastly superior, yet some folks still prefer softer cone materials.
Everything else being equal, (motor, frame, surround, spider, voice coil, etc) a metal cone will have a more accurate waveform reproduction, but will have a breakup node resulting in a peak in the frequency response. A poly cone will have no breakup node, but will have the information loss resulting from energy storage mentioned above. A frequency peak is just as much considered a form of distortion as information loss, but there is a difference: A frequency peak can be corrected with the right filter components, but information loss can't.
The key to this article is to explain why people have a preference. Reasons that some people prefer poly cones can be broken down into two main points. 1)Poly cones are easier to cross over. No harsh breakup node to deal with. There are even a few cases where a poly cone low pass crossover can simply consist of a single inductor. 2)Some music simply sounds better when reproduced through softer cones.
#2 is the key. How can music sound better when it is distorted? Well, when the original recording is poor, a metal cone isn't going to do much to conceal the distortion. Sharp abnormalities in the waveform come through loud and clear with a metal cone. Also, some amplified instruments introduce their own distortion which is all too audible and fatiguing unless we have a soft cone to "round the edges" in the waveform.
A word about the phrase "metal sound". Some metal drivers have been accused of having a metal sound. Most often, this comes about from poorly designed crossovers that do not address the breakup node. Sometimes, "metal sound" might come from drivers that seem properly filtered but in reality are crossed over too high. A breakup node can be notched out, but the 2nd and 3rd harmonics can't. If the intensity of a metal cone's breakup node is very high, a crossover point of greater than 2 octaves below the breakup node will make the 2nd and 3rd harmonic distortion too audible. Other than that, metal cones can simply be described as detailed or accurate, sometimes *too* detailed or accurate for a person's taste.
There you have it. Aside from the fear of complicated crossovers, the kind of cone material you prefer is probably more influenced by the type of music you listen to than anything else. High distortion amplified instruments need soft cones while better recorded acoustic instruments will sound more lifelike with stiff coned drivers. Summed up even more, rock recordings need poly, classical or jazz recordings need metal, and those who listen to a wide variety of music may do well to chose one of the composite cones.
It's hard to generalize, as every material has variations in stiffness. For example, polypropylene can be formulated to be stiff and fragile, while some metal cones can be thinner or use an exponential profile to dissipate breakup nodes. I can however name a couple of common drivers representing the norm: a Vifa P17 poly cone or a Seas L17 aluminum cone. No two drivers of similar size could be further apart in the way they sound.
Personally, I prefer metal or other stiff cone materials as it suits my music tastes and I generally do ok on the crossovers that deal with breakup nodes.
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