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This thread has been created to share my experience with the evaluation of two currently available phenolic ring tweeter (PRT) types as potential replacements to the original AR4x tweeter. Many 4x owners have experienced the demise of their original tweeters and seek alternatives to originals that are no longer available, except as used goods thru on line re-sellers.I will cover the investigation over a number of posts to follow because the volume of test data I present will simply be too much to include in one, initial post.Many readers of this thread may not know that two versions of PRT are available. Parts Express sells perhaps the most common one known. It's their 8 ohm p/n 270-252 http://www.parts-exp...tnumber=270-252 a nice bargain priced tweeter that conveniently has the same bolt mounting pattern as the original AR tweeter; thus making it a convenient, economical drop in replacement. This is most likely a S.E. Asia mfg. version of the original CTS PRT. The second, and perhaps less well known source, is Midwest Speaker (p/n MT-4107-8) http://w.mawebcenter...07-tweeter.html. MW also has a 4 ohm version, but that one was not included in this investigation simply because the AR4x is an 8 ohm speaker.Although both tweeters look exactly the same, and both are manufactured in S.E. Asia, their acoustic characteristics are surprisingly quite different. As such, utilization of each requires a different HP crossover for optimum results. Otherwise, harsh, unacceptable performance could be realized by an unsuspecting AR4x owner who simply switches out the dead original tweeter for one of the PRT's. I have been able to identify xo's that yielded reasonably flat FR and pleasing to listen to sound. [disclaimer note: the tests I share in this thread and xo's shared in subsequent posts represent one data point on each driver in my possession and may not be generally representative of these tweeter's performance characteristics] With Kent's help (AR4x original tweeter loaner), I was able to run electrical and acoustic tests on his, the PE PRT and the MW PRT. The impedance/phase tests results below show how the 3 tweeters compare. The PE tweeter's resonant frequency is much the same as the original 4x tweeter at about 1200 hz. However, the MW tweeter's resonant frequency is 3300 hz.