Looking for input: Best material for mid range cone


I had a surprise last night when I switched speakers in my system.  I've got a few pairs, but had been listening mainly to some Ascend Sierra 1, which have a polypropylene cone with a soft dome tweeter in a bookshelf design.  Anyway, I've got a pair of Tannoy Precision 6.1's, and swapped them in.  

The sound was noticeably different.  Piano sounded better, vocals had a finer quality as well, and the whole sound seemed a little more lively.  Now the Tannoys have silver interior wiring, a titanium tweeter in a coax design and are only rated for 75 watts. The cone material is some kind of pressed paper fibre.  And they are voiced to somewhat push the midrange.  But the sound was compelling.

I'm just wondering about cone material because some old Paradigms with Polypropylene were really not up to snuff, but they were quite old.  Any thoughts?
213runnin
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Polypropylene not so good above 1Khz.

Basically most speakers have too large a mid range for the bandwidth they carry (results in beaming)

Stiffer materials can measure extremely well (detailed) and have wide bandwidth often extending higher in frequency but tend to have resonances or ringing (poor timbre hashy sound).

Softer materials with weave or fabric or pulp paper mash can be great because of internal damping (get very clean background or exceedingly good timbre)however they suffer from linearity issues (limited bandwidth due to breakup)

In a three way softer materials for cones can work extremely well. In a two way stiffer material is often the best compromise to coverthe audible range in only two drivers.
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.