ReliaBill Engineer Posted March 21 Report Share Posted March 21 3 hours ago, RoyC said: Agreed...which is pretty hard to do if one has no experience with either tweeter in the 4x. Meaningless debates based on speculation and conjecture are distracting. The Mods and Tweaks section is probably the only place for this to go. Exactly why I just posted my comment to genek. Distraction from WHAT??? Isn’t this thread all about a MODERN replacement tweeter for the 4x??? Speculation? Conjecture?? Wouldn’t that apply to ANY and ALL modern tweeters you care to name?? So why get defensive? Why be so trigger happy?? Why be so contrary? It’s as if you’re waiting to pounce on any and all suggestions, no matter what or from whom. Sheesh! All I’m doing is starting from one particular tweeter that has long been suggested, and sold, as a replacement tweeter. So if I’m successful in making it sound more agreeable, how is it a BAD thing?? SMH Quote Link to comment Share on other sites More sharing options...
genek Posted March 22 Report Share Posted March 22 The question posed by the OP was whether there's a modern tweeter that sounds like the original, whether it's a drop-in replacement or not. If you look at past discussions, you'll find more than a few about how to create adapter plates and crossover mods to make various modern drivers sound like hard-to-find originals. And if your project ends with you posting a response curve for a modded PRT that matches that of the original tweeter, there will probably be a lot of people congratulating you because they think it's a very good thing. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 22 Report Share Posted March 22 Just waiting for my 4x speakers to arrive. They’ll need some work. Modified PRT ready for testing. Not including curing time, took less than an hour for the modification. Pretty quick, really. I spent more time experimenting with materials than the actual mod. Over the past 10 years, I’ve spent many hours studying, researching, testing, repairing, phono cartridges, 1956-2020 vintage. You learn a great deal about materials, resonance, electrical and magnetic circuits. Just a few of the mounted cartridges. Every one has been repaired in some way. MM, MI, Ceramic, Electret. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 22 Report Share Posted March 22 Decided to give the tweeter a test drive. Used my 2ax speakers. Disabled the super-tweeter using the pot, already had the AR mid-tweets disabled, wires disconnected and running out behind the mid-tweets. It should be a relatively good test run. The 2ax is a 2-way at its heart. The mid-tweet is a nominal 8 ohm driver (6.6 ohms DCR). I used a 60 ohm resistor across the PRT terminals reducing its DCR to 6.5 ohms from 7.3 ohms. Tweets mounted on the top of the cabinets in acoustical (leftover from room treatment panels) foam blocks. Crossover should be around 3000 Hz using the 6 uF capacitor. At the 70% Mid-pot position, this modified PRT sounds quite good! I did the same for the other 2ax speaker, but used the stock PRT. Comparison using a mono signal source, same to both speakers, switching between L and R, reveals a difference between how the 2 PRTs sound. The stock PRT is brighter, with a seeming larger suck-out in the midrange. My modified PRT has a much more present midrange and less bright, smoother treble. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 23 Report Share Posted March 23 A YouTube sound clip. Mono signal. 2ax supertweeter disabled. Mid-tweet disconnected. Output of internal mid-tweet crossover connected to modified PRT, which is mounted in foam on top of the cabinet. Mid-tweet pot at 75%. Quote Link to comment Share on other sites More sharing options...
RickB Posted March 23 Report Share Posted March 23 Sounds really good! Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 24 Report Share Posted March 24 5 hours ago, RickB said: Sounds really good! Thank you! Ive been playing it all day. In our basement. Allowing for some break-in time. The tweeter has opened up more. I turned it down to 70% from 75% on the level pot. It has a “big” sound, not what I’d expect from a small, inexpensive paper cone tweeter. So I’m hopeful. It fills the room nicely. I’ve played trumpet music, piano, big band jazz, various vocal with some that can exhibit sibilance on “S” sounds. All of them sound natural, easy, clear, with a wide and open sound. Even after several hours watching basketball on the TV with its sound on mute, listening to many records, the tweeter was never fatiguing or strident. (I can’t say that for the stock PRT. I had to disable it.) So I think the wool felt batting inside the cone and treated silk surround worked nicely! We’ll see when I’m able to mount it in the 4x. I have no idea if the tweeters work in the pair I have coming in. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 27 Report Share Posted March 27 For those perusing this thread. The PRT 8 ohm tweeter: Quote Link to comment Share on other sites More sharing options...
newandold Posted March 27 Report Share Posted March 27 38 minutes ago, ReliaBill Engineer said: For those perusing this thread. The PRT 8 ohm tweeter: I grew up starting in 1963 with the 2a then later, the 4ax and the 2ax. So that being said, I’ve got a soft spot in my heart for any and every effort to keep those old things going. even though I migrated to Allison acoustics I’m not one of those who attempts to restore the actual drivers, but instead made a career out of eBay shopping to enhance my emergency stash. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 28 Report Share Posted March 28 Allison made very fine speakers! I used to frequent an upscale audio shop in downtown Annapolis, MD, that sold Allison. I really loved the Model 2! I listened to my first CD in 1983 on those. Alan Parsons Project “Eye In The Sky”. It was a revelation! Im very tempted to buy a pair of 2s I saw for sale. Quote Link to comment Share on other sites More sharing options...
newandold Posted March 28 Report Share Posted March 28 10 minutes ago, ReliaBill Engineer said: Allison made very fine speakers! I used to frequent an upscale audio shop in downtown Annapolis, MD, that sold Allison. I really loved the Model 2! I listened to my first CD in 1983 on those. Alan Parsons Project “Eye In The Sky”. It was a revelation! Im very tempted to buy a pair of 2s I saw for sale. I had the big brother A1 for 35 years. If you go for it, make sure the 8 inch woofers are original. They should be 16 ohm drivers parallel wired. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted March 28 Report Share Posted March 28 They’re original. Need a refoam, though. But that’s always better than someone else’s botched refoam, and usually means original woofers. Quote Link to comment Share on other sites More sharing options...
newandold Posted March 28 Report Share Posted March 28 6 minutes ago, ReliaBill Engineer said: They’re original. Need a refoam, though. But that’s always better than someone else’s botched refoam, and usually means original woofers. Agreed and you should be good to go. The midrange and tweeters are interchangeable with the other original three-way Allison’s one, 3 eight and nine (if you decide to do a little spare driver shopping) Quote Link to comment Share on other sites More sharing options...
scottie munoz Posted April 12 Report Share Posted April 12 I'm gonna jump in here. I saw this topic some time ago and recently, I removed the grills off a couple sets of 2AX mid tweeters ( soaking any cage whether it's an AR-3A or 2AX mid-sweeter and methyl echyl (sp) solvent removes that epoxy like nothing else. I then use a reasonable amount of clear epoxy theory attached and a lot better But that's besides the point. Long story short I had a NOS 4x tweeter sitting next to me. And without the cage and insulation of the 2AX mids here I was able to see the diameters for what they were and their identical. The 2ax mid/tweeter is also used as the tweet in the AR-2X. Could this be a possible replacement? Impedance are the same. They're both cones and as far as fit in the hole would be a drop in replacement. *** I just went back and saw that recently "reliablebillI" ( who seems to know his stuff but damn it, learn to play well with others man) I guess he didn't have his 4x's yet ( which makes me wonder what the point of this was to begin with If you didn't have a set of 4x's why were you looking for a replacement tweeter for the 4x, and or getting everybody rolled up with the PRT situation anyways) yet so he was using a 2AX with the Super Tweeter disabled to see if the PRT would work blah blah blah, when is it was sort of on the nose that the next response was mine having not read that suggesting the use of the 2AX mid-tweeter as an actual replacement. which is sort of on the nose considering I'm suggesting actually using that mid tweeter as a replacement itself? I do recognize I don't believe that mid-tweeter would go up much further... It def. doesn't go up to 20K. somebody else probably knows the answer. There's a ton of them around and their cheap as well curious anybody else's thoughts as a 4x replacement. Second thing is like I said I have a single NOS 4X Tweeter, (You know that I think about it I actually own a set of Nos 2ax mid tweeters as well) still in the shipping container If anybody wants to use that as a reference in this project as opposed to these degraded 4x tweeters, I'd be willing to let someone use it to test. Scottie Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted April 13 Report Share Posted April 13 The 2ax mid-tweet is not the same as the 4X tweeter. So kind of pointless. Fits the hole, yes. But fitting the hole doesn’t mean it’s a replacement. As has already been mentioned in here. That’s why I’m modifying the PRT. But welcome to the party! And yes, I have a pair of 4X, so not pointless. The impedance are not the same! My 4X tweeter measures 4.7 ohms DCR. My 2ax mid-tweet measures 6.6 ohms DCR. I used the 2ax as test bed, just to listen and compare. Just to listen for the PRT’s (modified and not) overall sound from 1400-20K, since it plays well with the existing 2ax crossover values. It’s a very valid comparison. I know the 2ax inside and out, so I could compare the PRT to the AR sound. Listen for problems from the PRT as it does the work of both the AR mid-tweet and super tweeter. And a low crossover point near the free air resonance of the PRT. I do this as a hobby, at present. So I can afford to put in a lot of time, and it doesn’t cost me shop time. I don’t have to pass the time/cost on to customers. Scottie, you run a business, as of February 2024. Comparing 4X to the 2ax: 4x tweeter: 4x tweeter vs PRT: 2ax mid-tweet. Not the same as the 4X. Very different! There is a definite reason that AR went to the trouble of adding fiberglass batting to this mid-tweet and creating a cage to hold it. Also in using a glue to hold the cage that absorbs/damps vibration. Epoxy is too hard, and will not damp vibration transmitted into that aluminum expanded metal cage. Epoxy is difficult to remove without causing damage. The fiberglass pad is there to attempt better dispersion from the paper cone, and damp resonance that it has inherently. Removing the pad will not help it to mimic a 4x tweeter. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted April 14 Report Share Posted April 14 Replaced the corroded pot. But all else is original. Original drivers, original capacitor (20 uF spec’d, measures 22.3 uF), original rock wool batting. 1.03 mH inductor. So this is my baseline for comparing a replacement 4x tweeter. I think that’s a valid comparison. Not a “shot in the dark” comparison. When this original AR tweeter is damaged, or beyond repair, and replacements are few and far between, or perhaps above your price point, what do you do? Thats the question asked in this topic. Quote Link to comment Share on other sites More sharing options...
genek Posted April 14 Report Share Posted April 14 Is it actually rock wool (grey with little bits of, well, rock) or fiberglass? Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted April 14 Report Share Posted April 14 12 minutes ago, genek said: Is it actually rock wool (grey with little bits of, well, rock) or fiberglass? It’s what was in these originally. Looks identical to the rock wool insulation installed in my attic back in the 1950s; house built in 1931. Quote Link to comment Share on other sites More sharing options...
genek Posted April 14 Report Share Posted April 14 By the time the 4x came out in 1965 the era of rock wool should have been over. It was mostly used in the 50s and early 60s when fiberglass was in short supply. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted April 14 Report Share Posted April 14 1 hour ago, genek said: By the time the 4x came out in 1965 the era of rock wool should have been over. It was mostly used in the 50s and early 60s when fiberglass was in short supply. I’m not used to seeing so much very fine dust when using fiberglass in a sealed box. Abundant here. The texture of this is very grainy and more crumbly than fiberglass. More easily compressed than fiberglass. Fact is, I had to be careful when putting it back in before reinstalling the woofer. It compresses very easily. It’s exactly the same batting as was used in my 1965 2ax’s. So what’s the verdict? FG or rock wool? (Doest’t matter for these tests, since I haven’t changed it.) Quote Link to comment Share on other sites More sharing options...
genek Posted April 15 Report Share Posted April 15 It does sound like rock wool, and I think I can see crumbly bits that you don't expect to find in fiberglass. Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted April 15 Report Share Posted April 15 I put more info in Mods & Tweaks. But here is the mod’d PRT. With original AR wax-paper cap and original batting, new pot: Quote Link to comment Share on other sites More sharing options...
ReliaBill Engineer Posted Thursday at 05:55 PM Report Share Posted Thursday at 05:55 PM Bought a few (25) of the 2” paper cone press-fit tweeters to play with. $1.50 each. Built very similar to the AR tweeter. Just no face plate. 6.05 ohms DCR. Using the 12.5 ohm audio grade resistors in parallel, the DCR is reduced to 4 ohms DCR. ( I stockpiled these resistors. 40 of them.) So it should still play nicely with the AR-4X 20uF capacitor in the AR crossover. I’ll wire one up and have a listen, comparing to the original AR-4X tweeter. Quote Link to comment Share on other sites More sharing options...
JKent Posted Thursday at 11:03 PM Report Share Posted Thursday at 11:03 PM This is a bit OT but it’s sort of relevant: I don’t know what happened to Gene’s post suggesting those tweets might be appropriate for MicroStatic supertweeter clones, but they’re exactly what I used. Had a pair of MicroStatics with fried tweets so I needed EIGHT replacements. These fit the holes perfectly but had to be glued in place. I think they’re fine. Quote Link to comment Share on other sites More sharing options...
genek Posted Thursday at 11:47 PM Report Share Posted Thursday at 11:47 PM Forum glitched this morning. Hopefully, that was the only thing that got lost. Quote Link to comment Share on other sites More sharing options...
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