Thoughts on adding a Super tweeter .

Depends on the horn speaker!

Horns are designed to work over a fairly narrow frequency band. If the wavelength is too long to fit the horn, the horn won't effectively couple the motion of the cone to air. End result is - sound is attenuated at that freq. and below. The same situation happens with high frequencies - short wavelengths bounce around chaotically in the horn - again it fails to couple cone motion to air - and again you get rolloff.

Some horns are designed for high frequency extension, but most horns I have heard do not do very well above 10-15kHz. If this is the case - supertweeters, or even normal tweeters with a HP filter, will work quite well.

The only loudspeakers that are hard to add super tweeters to are ones with cabinets that dont allow super tweeters to be close to main drivers plus you need to beable to move the tweeter to ajust time arrival. A full range driver and horns are fairly easy to match too because of hi-frequincy roll off.If you have good extention above 25khz I wouldnt add one but most loudspeakers dont and many dome tweeters roll off far below this even if manufacter states 20khz is probly at -3db or greater. And off axis drop is is even lower for many domes.

Johnk...The wavelength of 20 KHz is about 2/3 inch so a supertweeter movement of 1/3 inch represents a 180 degree phase shift. Since the supertweeter and the tweeter are not exactly colocated even a small change of listener position will alter the phase relationship.

We really can't hear the frequencies that the supertweeter produces, yet I agree that it changes what we do hear. I think that the ultrasonic energy sensitizes the ear to the fact that something is going on up there. Then the sense of hearing creates what ought to be there in terms of harmonics of lower frequencies. If this is true phasing is unimportant. Some speaker systems that have supertweeters have them mounted on the back. Clearly phasing is completely random for such a speaker. Small movement of a forward firing supertweeter may affect the sound because of beaming, rather than phase change. This is why rear firing supertweeters are used.

Most loudspeaker are not flat on axis to 20khz, off axis even less so, so many super tweeters are running in the range we can hear, we custom set crossovers but many are arround -6db at 15khz.Then phase maters but crossover 25khz higher not as much.