michiganpat Posted October 14, 2011 Report Share Posted October 14, 2011 so I happened across a lot of 4 3/4" tweets like what's used on the 2ax and 3a's...2 work, but have broken flanges and smashed domes. 2 do not because the fragile leads are broken, but are cosmetically perfect. I took one of the non-working ones apart, and found the break, it was right at the foam suspension. I've repaired the break, and have continuity in the voice coil, but now what do I do to reattach/recreate the foam suspension? the 3 thoughts I had were in this order: fabric "puffy paint", as it puffs to a spongy interior with a solid skin exterior like the original, some "great stuff" minimal expanding foam (remains flexible after it cures), or some elmers' glue or latex/acrylic paint mixed with shaving cream (basically home-made puffy paint), or dabs of silicone RTV...anyone else have a better idea?Also, the foam under the dome just crumbled, like a piece of dry cake. it's density looked to be pretty close to that of the sponge applicators sold with automotive wax, so I was thinking of sacrificing one of them to replace the under-dome foam button. are the 2ax and 3a tweets the same part number and impedance? all of the ones I have (the 2 that work and the 1 I fixed) have a DCR less than 4 ohm... Link to comment Share on other sites More sharing options...
RoyC Posted October 16, 2011 Report Share Posted October 16, 2011 so I happened across a lot of 4 3/4" tweets like what's used on the 2ax and 3a's...2 work, but have broken flanges and smashed domes. 2 do not because the fragile leads are broken, but are cosmetically perfect. I took one of the non-working ones apart, and found the break, it was right at the foam suspension. I've repaired the break, and have continuity in the voice coil, but now what do I do to reattach/recreate the foam suspension? the 3 thoughts I had were in this order: fabric "puffy paint", as it puffs to a spongy interior with a solid skin exterior like the original, some "great stuff" minimal expanding foam (remains flexible after it cures), or some elmers' glue or latex/acrylic paint mixed with shaving cream (basically home-made puffy paint), or dabs of silicone RTV...anyone else have a better idea?Also, the foam under the dome just crumbled, like a piece of dry cake. it's density looked to be pretty close to that of the sponge applicators sold with automotive wax, so I was thinking of sacrificing one of them to replace the under-dome foam button. are the 2ax and 3a tweets the same part number and impedance? all of the ones I have (the 2 that work and the 1 I fixed) have a DCR less than 4 ohm...Pat,The AR-2ax/AR-5/LST-2 tweeter is an 8 ohm driver (dcr around 6 ohms) and the 3a/LST tweeter is a 4 ohm driver (dcr around 3 ohms). Assuming you can center the voice coil, the suspension material you choose will have different mechanical properties than the original foam/butyl combo, which will alter the tweeter's characteristics. What you are attempting to do is not easy. Roy Link to comment Share on other sites More sharing options...
michiganpat Posted October 16, 2011 Author Report Share Posted October 16, 2011 Pat,The AR-2ax/AR-5/LST-2 tweeter is an 8 ohm driver (dcr around 6 ohms) and the 3a/LST tweeter is a 4 ohm driver (dcr around 3 ohms). Assuming you can center the voice coil, the suspension material you choose will have different mechanical properties than the original foam/butyl combo, which will alter the tweeter's characteristics. What you are attempting to do is not easy. Royyep, that's what I figured....I was incorrect, I went back and checked, and 2 of the tweeters that don't have an open measure out at ~6ohm DCR, and the one I was able to fix the break on is ~2.9...the two that work, the foam dots are seriously deteriorated. interestingly enough all 4 tweets look to have clear rubber cement over the voice coil gap to seal it out...is that factory?I had a little setback, after extending a short lead on the 4 ohm tweet, the wire broke off right at the coil, and I can't find the end....sooo...looks like my experiment is bound to fail. bummer, as the 2 working tweets have smashed domes and cracked frames, the 2 non-working are perfect appearance wise....I've thought about cutting the voice coil off the non working dome, and glueing the dome onto the working tweet, but that'll probably change response as well by adding significant mass to the moving assembly....oh well, I only have like $15 into it, I've tossed more money away on other hopless endeavors than this... Link to comment Share on other sites More sharing options...
tysontom Posted October 17, 2011 Report Share Posted October 17, 2011 the two that work, the foam dots are seriously deteriorated. interestingly enough all 4 tweets look to have clear rubber cement over the voice coil gap to seal it out...is that factory?I had a little setback, after extending a short lead on the 4 ohm tweet, the wire broke off right at the coil, and I can't find the end....sooo...looks like my experiment is bound to fail. bummer, as the "Repairing AR ¾" dome tweets…."Well, you're not the first to try to repair the AR hard-dome tweeter; had you succeeded, you'd be the first to accomplish it. No one has been able to successfully repair the tweeter and replicate the original's stellar performance, simply because no one has the alignment jigs, anechoic test chamber or capability of pouring an exact amount of 2-part urethane foam into each of the three gaps, followed by applying exact-amounts of butyl-rubber around the gap. It is possible to repair one to get it to work, but it would not sound like the original -- I've found this out several times. I mean, AR themselves wasted two or three tweeters for each good one they produced (bad ones could fortunately be recycled), so even the factory people had trouble with the difficult-to-build tweeter. Once you've opened up the tweeter, kiss it goodbye.Note the picture attached: AR rejected huge numbers of drivers just trying to get them to meet the minimum specifications of performance. You can imagine how difficult it would be to duplicate this effort at home!--Tom Tyson Link to comment Share on other sites More sharing options...
michiganpat Posted October 17, 2011 Author Report Share Posted October 17, 2011 "Repairing AR ¾" dome tweets…."Well, you're not the first to try to repair the AR hard-dome tweeter; had you succeeded, you'd be the first to accomplish it. No one has been able to successfully repair the tweeter and replicate the original's stellar performance, simply because no one has the alignment jigs, anechoic test chamber or capability of pouring an exact amount of 2-part urethane foam into each of the three gaps, followed by applying exact-amounts of butyl-rubber around the gap. It is possible to repair one to get it to work, but it would not sound like the original -- I've found this out several times. I mean, AR themselves wasted two or three tweeters for each good one they produced (bad ones could fortunately be recycled), so even the factory people had trouble with the difficult-to-build tweeter. Once you've opened up the tweeter, kiss it goodbye.Note the picture attached: AR rejected huge numbers of drivers just trying to get them to meet the minimum specifications of performance. You can imagine how difficult it would be to duplicate this effort at home!--Tom Tysonafter 40 years, I'd really question if ANY of these tweeters still have their OEM response, given the deterioration of the foam under the dome and the urethane foam suspensions....so then the question changes to, which would be "better", using a modern replacement tweeter with dissimilar response and crossover mods to better mimic the response (but not the original's dispersion, which I don't think you'll find in a modern driver), or repair/rebuild an original driver and potentially changing it's response from original? Link to comment Share on other sites More sharing options...
Carlspeak Posted October 17, 2011 Report Share Posted October 17, 2011 after 40 years, I'd really question if ANY of these tweeters still have their OEM response, given the deterioration of the foam under the dome and the urethane foam suspensions....so then the question changes to, which would be "better", using a modern replacement tweeter with dissimilar response and crossover mods to better mimic the response (but not the original's dispersion, which I don't think you'll find in a modern driver), or repair/rebuild an original driver and potentially changing it's response from original?I'm not sure how to answer that ? except to say: for most of us, doing restoration/s is a hobby rather than an avocation, and as such, it should not be a question of either/or. Rather, in this case, you have the option to try both approaches. We'd love to hear your opinions on the outcome of each. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.