My replacement tweeter had the same DC resistance, same impedance at 1kHz, same efficiency and the same build (short horn), but result was strange. I verified phase using small battery and magnifying glass. New tweeter had more pronounced very high frequencies, but there was suck-out at lower treble. I tried them in opposite phase, just in case, and suddenly everything is fine. They sound little louder and cleaner and that was my objective. I've done it before to Paradigm Studio 60 and I failed in spite of extensive changes to xover . It is not as simple as it seems and perhaps in your case it is just dried ferrofluid, if speakers are over 10 years old (or less if played very loud). You can find ferrofluid at Parts Express, but have to be very careful separating voice coil. Best to find somebody who does it.