Experience with adding super tweeter?

I remember the plasma. Ingenious (no mass!). But widespread use I think was also hampered by the Ozone (O3) that plasma 'flame' generates. Small doses are healthy, but higher/longer can cause problems (cance) IIRC?

Ozone (O₃) is a colorless to blue gas with a pungent odor. Exposure to ozone may cause headaches, coughing, dry throat, shortness of breath, a heavy feeling in chest,  and fluid in the lungs. Higher levels of exposure can lead to more severe symptoms. Chronic exposure may lead to asthma. Workers may be harmed from exposure to ozone. The level of exposure depends upon the dose, duration, and work being done.

Ozone is used in many industries. It is used for purifying air and drinking water, in industrial waste treatment, oils, bleaching and waxes, and to make other chemicals. Some examples of workers at risk of being exposed to ozone include the following:

• Outdoor workers in areas with high levels of ozone
• Factory workers in paper and pulp mills
• Workers in waste water treatment plants
• Fisheries workers who treat storage water

Love the addition of my supertweeter to my modded Aerial Acoustic 7ts..  My current one is the Enigmacoustics.  Definitely more air, top end and delicacy.  When I started a thread on this topic, I got posts telling me that it is not possible for me to hear high frequencies and it's just impossible for the supertweeter to make a sonic difference.  Ignore the naysayers if they chime in.

"not hear high frequencies" is certainly nonsense. Just use a cheapo old fashioned equalizer and pull down the "16k" lever while pusing all others up. Then listen to a violin (or pretty much any other instrumetn/music). 

@kraftwerkturbo I helped set up a pair of Hill Plasmatronics. They never show you pictures of the nitrogen tanks out back and they were not particularly well made. They were ugly as hell and most of what you were listening to was regular dynamic drivers and crossovers. Only the tweeter was plasma and they were worse than impractical. 

Most old people can't hear a thing over 12 kHz or even lower. It is called presbycusis. If a speaker requires a super tweeter it is a bad speaker. The "air" frequencies are in and around 6 kHz. Adding more "air" might seem pleasant, but it is distortion. You do not hear all that "air" at live concerts. 

The best tweeter made is the Magnepan ribbon tweeter. Magneplanar will not sell them separately. To get one you have to have the serial number of two 20.7s and there is a core charge. You have to send the old one back. A ribbon tweeter has to be at least 5 feet tall to be practical. Line sources beam vertically. You can not hear a thing but reflected sound above or below them which is why major speaker companies will not use them. At 5 feet you can cover both the seated and standing positions. Short ribbons have to be exactly at ear height.  

@mijostyn Even if we cannot 'hear' (correct: hear less) above 12k (or 16k for that matter), it is nevertheless a key part in any music. Simple test (already mentioned earlier): borrow a low fi graphic equalizer, push all levers UP, and the last one DOWN. Observe. Even an 80 year ("can't hear anythign above 8k"?) will immidately notice the difference. Or take a nice recoreding of a stradivari, and run it through a 12 db low pass digital filter with 16kHz. Those overtones (you call them distortion, the Stradivari owners will strongly disagree, as do most audiophiles) are actually key and truly 'make the difference'. "Adding" a supertweeter may or may not be the way to go; but relieving a heavy, big, lazy tweeter from the 'heavy lifting' above 10kHz for example is just as good and idea (potentially) and adding an 12inch driver to make life easier for that tiny 6" in your 2 way speaker.