What are the differences in Tweeter materials?

The main confusion with the soft dome tweeters is the misunderstanding of terms.
SOFT simply means what it says, soft, as opposed to hard.
TEXTILE simply means fabric. Ie. the industry that deals with the materials used in clothing is known as the Textile Industry.
So the terms Soft, Cloth, and Textile are all basically interchangeable.

It gets a little varied after that.
SILK is the specific material used in a Soft/Textile dome.
If the material isn't specified then it could mean anything but is most likely either cotton or some sort of nylon derivative.

Of course, no textile material is airtight without the addition of some sort of sealing material.
This is where POLYAMIDE comes into play. It's the glue that seals the textile in a soft dome.

All softdomes can technically be considered MATRIX materials. Matrix simply means that at least two different materials are mixed for mutual benefit. Fiberglass and Carbon Fiber are common examples of matrix materials. They mix a hard polymer with a flexible but strong cloth-like material. The polymer gives the cloth functional rigidity while the cloth material (the actual carbon or glass FIBERS) gives the matrix it's strength.

So, getting even more complicated, you can see that Carbon Fiber and Aramid (early Focal type) tweeters are sort of quasi soft/hard tweeters. They are matrix by design, just like Soft dome. But they are also rigid, like hard dome.
And they share pros/cons of both types.

Metal dome tweeters are typically made up wholly of whatever material they claim to be. Though not always. When the first Beryllium tweeters came out, only Focal had the technology to form pure Beryllium. So all others where hybrids. Though now others have caught up and there are others with pure Beryllium domes. Before Beryllium was Titanium. Titanium is also difficult to work with, though not nearly as Beryllium. It is also not toxic like Beryllium can be. And before Titanium there was Aluminum. Aluminum is by far the easiest metal to shape, but it comes at the cost of rigidity.

The whole idea with tweeters is to basically have the material be infinitely rigid while being zero mass. So you start playing with the various properties of the material. Titanium is heavier than Aluminum, but it is also many times stronger. So you can use much less of it, thus bringing the overall mass down for a given stiffness. Beryllium is even better.

BUT, as most people notice, all of this metal stuff comes at a cost. That being ringing. But that's a whole other subject.......

@ Prdprez,

Thanks a lot! Your post was very interesting and informative. I learned much from it.

Well, I'll chime in, I've built with several tweeters and can speak from experience about some of their general characteristics... remember, no absolutes here, if you change the dampening material on any dome, the dome's sound changes. Let me preface this by also saying that I have never personally paid more than $100 or so for a dome, so my experience is limited to that, yet I have personally used dozens upon dozens of tweeters.
In general, the harder the material, the higher the material rings. You will see many metal domes that have a rise and some have a break up very high. In general, the harder materials have a more detailed sound, which is why you've heard that many hard materials can sound harsh. If a hard dome, whether diamond, ceramic or metal is properly damped, it should be very detailed and today, well damped hard domes are capable of some of the most detailed sound while remaining smooth with the right gear and front end. A great 3/4 inch metal dome is Hiquphon.
My least favorite domes have been mylar domes, cone breakup is very audible and these cones can't be pushed. Treated fabric has been mastered. I particulary like some of the better Seas and a Peerless HD (now scan speak), but many companies make a great fabric dome. While a fabric dome typically is not as detailed as a metal in the last degree, they are none the less, detailed, have an extended high end and offer low resonance so they can be crossed over with a variety of drivers.
Ribbons, are very fast & smooth sounding, but typically have a large variance in response curve and unless you use notch filters, most ribbons have peaks that I have found undesirable. Most ribbons also have a higher resonance hence they cannot be crossed very low. I have no experience with the mega buck ribbons and yes, they seem to have curves that affordable ribbons can't match.
Remember, these are very general statements and anyone with real experience could find a single driver to challenge a statement here. I hope this helps, Tim

@Timlub,

Thanks for your post. My favorite soft domes have been from Dynaudio, Morel, and ScanSpeak. I find a lot of todays Seas soft dome tweeters to sound a bit on the bright side. I was not happy when Spendor switched from ScanSpeak to Seas for their tweeters. Especially in their Classic line. They always used ScanSpeak. I have a pair of Proacs that also uses the 3/4 inch ScanSpeak. Great tweeter. Wonder if they are still in business or did they get bought out by Peerless?

Mezzanine,

I'm glad you posted. My comment about the secret pricing structure, I hope, was taken just as some light hearted humour, and nothing more. Someone always seems to be complaining and/or joking about the high cost of some equipment, I just couldn't resist.

Unless I misread your post, it looked like you were trying to compare some of the more common materials to some of the more rare/exotic ones, with an emphasis on soft tweeters. API (Audio Products International), the parent company of several Canadian high end speaker manufacturers (Mirage, Energy, Paradigm, PSB and Athena are the ones I can remember. There may be others as well), make camel hair tweeters. They put them in Energy speakers and I think the original Mirage M series. I know several people that have these tweeters and swear by them. I'm not sure if they are currently going into any speakers but I'm pretty sure you can still buy the raw drivers.