Super Tweeters

Johnk,
To begin with, a lot of these supertweeters do have adjustments on them, and since you are only augmenting the highest frequencies that are likely not even being produced by your speakers tweeter, it is not like you were adding a "super midrange" (if such a thing existed) which would cause all sorts of problems obviously.
In the end, many have found them beneficial to the whole sonic spectrum, and if that conflicts with measurements that say it shouldn't be so, who really cares, except apparently yourself.

I think that these super tweeters are helpful to the aging population of hi-fi hobbyists. As we age (50+) we loose some high freq. hearing ability. These ST replace what we are loosing, and we like it. We should all set up our systems the way we like them. If we then tire of it, we change it. If you strive to maintain perfectly flat response and end up with a perfectly "flat" sounding system, you will probably start to explore areas of improvement for yourself.

Can cause destructive interference due to to far a distance between drivers and from drivers covering some of the same frequency not to mention the time error. Then you have the very limited efficiency of most ST again not going to match your loudspeaker unless both are designed as a whole. A driver doesn't allow you to hear ranges your not capable of hearing if they could there would be no hearing problems for one could just use a aid and wow you hear normal doesn't work like that. Last I post good luck.

One thing I like about Tannoy ST100/200 is eight selectable crossover points and sensitivity settings. In my application this made them a much better match than the Chinese Lucy ribbons. Correct time alignment can be obtained by varying front-to-back positioning on top of the main speaker. I mount them on an elevated platform to decouple from vibrations across the top of the cabinet.

An ST placed in parallel with the main speaker will change the impedance load on the amplifier. This may effect which amp impedance tap sounds best-- assuming that your amp has the flexibility of multiple taps.

Be aware that whatever cross-over point and sensitivity level is selected, there will be downward embellishment all through the treble region. Tannoy uses a third-order crossover. Their manual includes frequency plots.

Bottom line, the ST is a tool I would not want to be without.

From JohnK - "A driver doesn't allow you to hear ranges your not capable of hearing if they could there would be no hearing problems for one could just use a aid and wow you hear normal doesn't work like that."

What I'm saying is that the super tweeter is the aid. It's helping listeners with high frequency roll-off due to age. It's not like being deaf, where no driver is going to make you suddenly hear. Rather, it boosts up the areas where we are becoming weak in our hearing.