Thoughts on adding a Super tweeter .

I heard a super tweeter on a neighbor's SET system. Although there was
noticeable HF extension over his single driver speakers, the superimposed
lower HF brought on a heightened upward tilt that I didn't care for.

My experience is a bit different than most of what has been reported here.

I am definitely not an insect: my hearing dies well short of 15kHz, however the addition of the Townsend supertweeters to my Quads was a revelation: the entire sound stage became better developed (source is vinyl). I did not hear increased upper frequency 'hash': in fact the upper midrange is where I heard the most dramatic improvements (perceived improved clarity, lucidity). The overall effect: 'it sounds more real'.

I don't really 'hear' the supertweeters when listening, but it is quite noticable if you take them away. My non-audiophile wife was listening with me and clearly heard the difference when the tweets where taken out and put back into my system. I have also heard from other quad owners that the Townsend's enhanced their systems in a similar manner. The Quads do not have 'dc to light' frequency response so YMMV.

The addition of the supertweets is somewhat akin to the addition of a good, well integrated subwoofer; with a 'woof it's not merely the lower frequencies that are audibly improved, the upper frequency ranges also benefit.

I think this is one of those 'listen for yourself in your own system' situations. Supertweets cannot be dismissed as 'crackpot audiophile psuedoscience'. They can make an audible improvment in a high resolution audio system.

Cjsmithmd,et al...The reason for my post was for a couple of reasons(thanks to all,for responding).I have heard the Townshends(I like the Muratas,but they come in too low,to consider)in a fellow music lover's wonderful set-up.He was sporting the "shockingly good" Sonus Faber Extremas,a design long since gone(what a mistake,to discontinue these),and since I believe those had a tweeter roll off of 17khz,he gave the Townshends their day in court.BOY,the difference was NOT subtle.Better air/texture!For sure!Much more palpable.
So,with the non- stop talk of Berrylium/Diamond tweets,I simply felt,maybe,I could get that extra something,I read so much about.Bear in mind I felt my own speakers,which are flat to 25khz,had more air/extension,than the stock Extremas,but the Townshend demo was amazing.
Now,some time ago I added a Rel Stentor sub,to integrate with my system.I have my speakers almost 9 feet out from the rear wall,and have a very deep "stage presentation".However,as my speaker is a sealed box design,I suspected I could gain a touch(that's all I was looking for)of added heft/depth,in the lowest frequencies.
My friends were all dead set against this,as my speakers are amazingly fast,and articulate in the midbass.They did not think I could get a good blend.They were wrong,thankfully.Though it took me a long time to get past the "WOW I have loads of bass,and isn't it fun" factor.The blend is now,absolutely seamless,and hence my having a sneaky suspicion that I could pull a "touch" more off,in high freq air,or whatever.
Believe me,I could be making a mistake here,and am aware of it,as the Townshend comes in,and will overlap my own tweets by about 5khz.This can be trouble,and if my bass experience is an example(any overlap in low frequencies came off as "tubbyness") I can easily screw up something I have no actual criticisms of.YET,AND YET...I am always trying to push the envelope,and believe in my system.This could spell trouble,but as I see it,I may have to scratch the issue,or take a trial run.
I hope to get some meaningful feedback by those(few?)who have possibly tried or heard a supertweeter on a speaker with an,already extended high freq response.
Thanks,so much.

Tvad - You are right of course, I forgot about the high-res media.

Cj - Your experience is what I think is supposed to happen w/supertweeters. The ultrasonic frequencies they reproduce aren't supposed to be heard by themselves, but by their interaction with other frequencies. The best analogy is if you play the same note on 2 guitar strings that are slightly out of tune, you will hear a low frequency wavering. This is called a beat frequency by acoustic engineers (and has nothing to do with the beat of the music). The supertweeters are supposed to produce audible results by modulating the rest of the frequency spectrum. In order to do this, though, they must be fed a signal that represents the ultrasonic content of the original musical event. This is not possible with Redbook, but is with hi-res and probably vinyl