The R25 tweeters are 1" silk Domed bad boys.
The R19 tweeters are 3/4" silk Domed bad boys.
Kicker resolution series tweeters : R13, R19, R22, and R25. of this Bunch only the R25 and R19 are silk domed.
The silks cost more to build and they sound much smoother and have a better quality of sound than the other resolutions.
ND25 - R25a - ND25a - RND25 - and Rnd25a are all really just R25's - they were branded differently over a few years and for various sets. they are all 1" silk domed Kicker resolutions.
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The R22 is a 1" tweeter as well but it is not silk - sounds a little metalic to me really and i prefer the r25. But I have it like that. :O) I am the KICKER man.
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I noticed some one offering the r19 set for 70.00 bones - that's a nice set and if it were new that's a great buy.
I sell the R25's for 105.00 - I have two sets on eBay at this time but they are not all buy themselves - they each have a kx250.2 amp that goes with them. also I don't have any sets retail packed. i have them brand new deal bulk packed and I have the TWX454 passives that are included for lack of any other crossover.
at any rate - im just looking around here. LOL brand new to the site today.
I am going to go see what all you guys do on here.

i have the manuals for all this stuff if anyone needs PDF files and can't find them anywhere else. just gimme a yell and I will send.