Looking for input: Best material for mid range cone

It's all very subjective. Different strokes for different folks. Cone size plays a large role as well, as does the crossover implementation.

I find that paper and plastic cones typically produce the tonal qualities that I prefer, though I've heard some metal composite cones that sound close. 

One thing I noticed is that the BBC inspired brands (all commonly regarded as having excellent midrange quality) use either some form of plastic or paper composite for their midrange drivers.

@kosst_amojan,

If plastic is a miserable material for cones, why do British monitors such as Harbeth Spendor and Epos produce such an elegant midrange? Have you compared such speakers to Focal's Flax cones?  

Where do you guys come up with these blanket claims? "Polypropylene not so good above 1Khz." Based on what? My speakers have a 7" plastic cone and play up to 3kHz with hardly a lick of distortion. They play much cleaner than numerous other speakers I've heard with exotic cones. There's good and bad examples of almost every speaker diaphragm material. I've heard aramid cones that sounded like complete garbage, and some that sound great, the same for paper, plastic, titanium, and aluminum. I've owned speakers with plastic tweeters (oh no! Over 1khz!) that blew away some well regarded silk domes.

To my next point: size matters! Any loudspeaker engineer worth his salt can tell you that a material's performance can heavily depend on the size of the diaphragm, the frequency range it's asked to cover, and the SPLs it's asked to play. It's true that large plastic cones CAN struggle with higher freqs, while paper cones exhibit their best virtues in the larger sizes. I haven't heard many good sounding paper tweeters, however, like with most materials, I'm sure there's exceptions out there.

OP, 
It really comes down to personal preference and the quality of design. Speaker sound is the most subjective aspect of a system. One person's euphoric midrange will make another's ears bleed.

Poly cones can have huge variances in tonal qualities, just as other materials can.

The Poly cones of my Epos Epics sound different from those of my Spendors, which sound different from those of Harbeth. Polycarbonate has derivatives, similar to metal alloys. Then there's the effect of the basket material, the basket's frame design, the cone surround material, implementation of dust cap or phase plug, the spider, and the voicecoil design. All have an effect on the driver's sound. 

A plastic driver with bullet dust cap will have different tonal characteristics from one with a bullet phase plug. 

It's my opinion that the real test of  quality drivers (and components in general) is whether you can listen to them for long periods without fatigue, get lost in the music, and forget about the system. Often times, people automatically perceive "different" as being superior. Though, if they listen to these excitingingly different speakers for long periods, fatigue sets in, or they end up returning to their previous pair. You might find the Tannoys to be superior now, but consider how much time you've spent with them since swapping out the Sierras, and consider how you feel after a 2 hour plus listening session. You might be surprised if you swap the Sierras back in after a few weeks, then again, maybe not.

Generalizations in regard to cone material are just that: generalizations.

@russ751,

How can the Kipods be any good when made of such an antiquated material? Don't you know that good speaker drivers require super exotic composite materials, the more exotic the better......😂

@russ751,

You misread my post regarding aluminum drivers. It was sarcasm. I was referring to the fact that aluminum drivers are far from a new concept, yet many highly regarded manufacturers continue to use them in everything from bass woofers to tweeters.

I was making fun of some companies that use uncommom composite materials, often as a pure marketing ploy. They know the public majority has come to assume that any fiber composite material is inherently better than traditional materials, whether used for ballistic vests, car chassis’, or speakers. Consumers likes exotic materials because it leads them to believe they received a high-value product. Little do they realize that some of the best materials for speakers have existed for many decades. Some people read "hemp," "flax," "carbon fiber," "graphene," "Kevlar," and their minds instantly associate these less common materials with high performance and high cost. However, companies like YG, Revel, Spendor, Stirling Broadcast, ProAc, and others continue to prove that these materials do not necessarily perform any better as speakers than aluminum, plastic, or paper.

They don’t always understand that every composite has strengths and weaknesses and countless variations as already mentioned.