Free air resonance?


What is free air resonance and does it make a big difference if one tweeter's free air resonance is high or low? Would 1500 be better than 600 or vice versa? I am thinking of changing my Vifa's which came with my Hales T5's which have a free air resonance of 1500 or so to the Seas Millenium which has a free air resonance of 600.
Any explanation or advice would be greatly appreciated.
128x128mitchb
Mitch, I am not sure what the doctor has to say, but I emphatically feel that with all of the money you have invested in upgrading the crossover and wiring, considering the pretty high level of the Hales woofer and cabinetry, the weak point of your speakers at this point is clearly, Clearly, CLEARLY the tweeter.

Tweeters are the drivers that have possibly come the furthest in the past 10 years. And, they sure had far to come. At that time, the Dynaudio Esotar, Esotec, Morel MDT33, and ScanSpeak Revelator were the best you could get. Outside of the Esotec and Morel, none could really be considered reasonably priced, but all were MUCH (orders of magnitude) more expensive than the everyday Vifa/Seas/whatever metal domes in most speakers.

In your case, unfortunately, you were on the cusp of the arrival of the better affordable tweeters, but fell on the bad side of the fence.

JUST UPGRADE THE DAMN TWEETER!!!!!!!!!!!!!!!!!!!!!!!!!!!!! You'll love it! But, as I also told you before, please give it 50 hours before you really judge it.
I think you should go for it! Those tweets will surely out perform the stock tweets in your speakers. There's just some things charts and graphs cannot explain. If you use those things the good lord gave you on both sides of your head..I think you will be alright!

Or put the other way JUST UPGRADE THE DAMN THINGS!!! LOL

Good Listening!
I put in the Millenium tweeters about 10 hours ago and am extremely impressed and excited. Perhaps my speakers won't read well on paper if tested, I don't know but the sound is more sophisticated sounding. It is not "dark" or have lower levels of high frequencies. If anything what's not there from the old tweeters shouldn't be there. In other words with my crossover mods my Hales tweeters were sounding a little harsh but acceptable. Know the sound is smoother and yet very detailed. A pluck of a bass string sounds ever more like a pluck from a bass string. Symbols and other high frequency sounds sound more natural, less hyped. Piano notes actually sound like a piano.
I am pleased. I hope I like how they burn in.
Thanks to everyone for all your help and advice.