Pete B Posted March 21, 2008 Report Share Posted March 21, 2008 John (ARjohn) kindly sent me a .75" AR-2ax tweeter for dissection/analysis.The entire magnet assembly is potted into a plastic cup that is also themounting flange. The number 561-74??, is printed on the back. The lasttwo digits are blurred. probably 29. This driver was most likely manufacturedin the 29th week of 1974. Did these ever have a metal frame (cup)? Would liketo hear about the evolution of these drivers if anyone can comment.The plastic mounting flange was cracked in shipping unfortunately, even though it was well packed by John.There's about 1/4" of what looks like normal copper enameled magnet wireleft but I have read about aluminum wire being used in the 3a version. Didthe 2ax tweeter also use aluminum wire?I commented about this tweeer in another thread where I mentioned thatthere are 3 globs of foam (looks like urethane) attaching the dome to theframe. I also stated this in another thread: What I didn't notice is that thereis also a clear, cellophane looking layer where a normal tweeter's suspensionwould be. It seems to me that this layer is probably there to keep foreignmatter out of the magnetic gap as I doubt that it provides much restoringforce. The solid lead in wires being routed through the globs of foam whichwould help to keep the flex evenly distributed across the wire to reducebreakage. RoyC kindly commented to confirm these points. It has also beenmentioned that the clear coating was probably a butyl rubber material.There is about a .25" hole in the clear rubber edge of this tweeter, where thevoice coil windings can clearly be seen. Other than the whole in the clear edgeand the broken lead in wires this tweeter looks to be in very good shape. Thehole could probably be easily fixed, assuming that new lead in wires can alsobe attached. I could then measure the T&S parameters. The untreated holeacts as a leak in the chamber behind the dome. Link to comment Share on other sites More sharing options...
Pete B Posted April 10, 2008 Author Report Share Posted April 10, 2008 Roy has confirmed that the .75" 3a and 2ax tweeters both used copper wire not aluminum. There are threads about aluminum wire but it wasnot used in these drivers as I incorrectly stated above.There's enough wire left to repair this driver. I'm wondering what gaugeand type of lead in wire AR used? Was the solder joint just held down with the black electrical tape that is commonly seen? Link to comment Share on other sites More sharing options...
Pete B Posted July 25, 2008 Author Report Share Posted July 25, 2008 T&S Data is questionable since there is hardly any peak in the impedance curve:There was a clear peak at 2200 Hz, but it was very small due to perhaps dampingin the gap, or perhaps crumbled foam has dropped into the gap:AR-2ax .75" Dome Tweeter:Rvc = 5.62 ohmsFs = 2223 HzQt of .99Qm = 1.05Qe = 18.23Zmax = 6.88 ohmsZmin (passband) = 6.79 ohmsZ (at 10k) = 7.34 ohmsLvc = 39.4 uH at 10 kHz Link to comment Share on other sites More sharing options...
Pete B Posted July 28, 2008 Author Report Share Posted July 28, 2008 I have two more samples from my own AR-2ax's, they also show a very minor butmeasurable peak. Fs is certainly not very consistent and completely different fromthe previous sample.AR-2ax .75" Dome Tweeter:Unit = PLB #1Date SEP 28 1971Rvc = 5.60 ohmsFs = 4767 HzQt of .53Qm = .63Qe = 3.6Zmax = 7.06 ohmsZmin (passband) = 6.79 ohmsZ (at 10k) = 6.86 ohmsLvc = 28.7 uH at 10 kHz AR-2ax .75" Dome Tweeter:Unit = PLB #2Date SEP 28 1971Rvc = 5.56 ohmsFs = 5396 HzQt of .47Qm = .54Qe = 3.55Zmax = 6.92 ohmsZmin (passband) = 6.84 ohmsZ (at 10k) = 6.93 ohmsLvc = 30.2 uH at 10 kHz Link to comment Share on other sites More sharing options...
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