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RoyC

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  1. Your drawing looks good. Based on Carl's description of the response differences/similarities between the new and original woofer it should work as he described. Roy
  2. I'm very glad you asked that question. I typed in the wrong value (I just corrected it). It is .5mh, not .05mh. Your photo shows that you have the right components. The coil is absolutely necessary! It is not only important for the proper response, but to protect the tweeter. 20uf is a very large capacitor value to use without it.
  3. Good call...The large Industrial Condenser caps can be mistaken for Spragues, but seldom measure as well.
  4. -The woofer's + lead (red) and the tweeter's 20uf capacitor should connect to the cabinet's + input terminal. -The two black leads connect the cabinet's - input terminal to the - sides of the tweeter and the woofer respectively. -The 3 ohm resistor (not shown) is connected in series via the yellow (+) tweeter wire emerging from the junction of the cap and .05mh coil. The resistor can be placed anywhere before the tweeter's + side along that yellow wire. -As shown in the photo, the .05mh coil is also connected to the cabinet's - input terminal along with the 2 black - wires. It is in parallel with the tweeter, which means it is connected to both sides of the tweeter circuit (- and +). Carl was using a new Advent replacement woofer with no inductor. The only crossover components would be in the tweeter circuit (ie the 20uf cap, .05mh parallel coil, and 3 ohm resistor). Roy
  5. 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.
  6. Yow...Now who is being "defensive"?! None of that post was meant to be a justification for you (or anyone else) to not work with the tweeter! If you take another look, you will see that the second part was information pertinent to Gene's (correct) assumption that there is no other data from the sellers of the tweeter...despite its obvious popularity. I was not defending the tweeter, and it was not a criticism, implied or otherwise, of your project. SpeakerDave and Carl Richards were redesigning the 4x crossover with actual measurement equipment and calculations when the PRT tweeter was first introduced. They even had AR speakers to work with...imagine that! It was very credible work from guys with professional experience in the audio field. Unfortunately, like your project, it was only of some interest to us geeks. Since that time the PRT tweeter has become established as a popular replacement, like it or not. You are just late to the party with far fewer tools. Carry on, it will be entertaining if nothing else.
  7. Whatever... I believe there were measurements posted way back when SpeakerDave, carlspeak, (and others?) were recommending crossover changes. The bottom line is the recommendations apparently did provide a smoother system response, but I'm not aware of anyone who implemented them. The crossover change was not just a simple tweeter capacitor swap, and the primary issue was a peak in the upper midrange response of the PRT. I also seem to recall the availability of other PRT tweeters at the time with similar, but somewhat different, response characteristics. To Gene's point...I just had a conversation with "Vintage_AR" (Larry Lagace), and told him about this thread. He just laughed and said he sells "lots of them" and has never had a return or a complaint. I then went to the Parts Express website. Here is the description: "At last, a faithful reproduction of the classic "phenolic ring" tweeter developed by CTS and used by Marantz, Altec, Martin, Acoustic Research and many others." ...where it gets decent reviews. Low cost and ease of installation has obviously made this a popular way to repair the 4x, especially since used original 4x tweeters have become very scarce. Roy PS Hmmm...In case it isn't clear, I have never had any involvement in the sale of this tweeter (modified or otherwise).
  8. I do that work for Larry/Vintage_AR, and I know for sure the 3a/LST type of mid cannot be rebuilt. Occasionally they can be repaired if they are not functioning properly. Fortunately, they are reliable and don't suffer the same type of degradation as the AR-3 mid, which can be refurbished. The construction of the 3 mid is very different than that of the 3a. You may have seen the AR-3 mid listing. Roy
  9. "A smooth tweeter is a smooth tweeter....... Not so much to state definitively the merits of one over the other. Pistonic motion was the point of the comparison I was making. Unconstrained (but damped) motion of a tweeter cone/dome provides the best chance for smooth FR output." You started that part of the conversation by telling us about AR's use of inferior cone-type tweeters, and conjecture as to why AR did what it did with the 2ax mid and 4x tweeter (along with other generalizations and suppositions about AR designs). Too bad so many speaker companies and their design engineers didn't have access to "smooth" tweeters over the decades. Why not just recommend your favorite dome tweeter instead of rebuilding an inferior cone replacement tweeter with which you have no experience to be adapted to a speaker system you have never owned and have no access to? It would likely be easier for someone to make cabinet changes than to rebuild a less than desirable new replacement tweeter. Personally, I would be more inclined to investigate the driver PeteB (many credentials, btw) mentioned earlier in this thread if that were the case. ...Yet already it seems a judgement has been made about the merits of doing this, and its level of complexity. Prejudged, if you will. Perhaps, but most likely based on your participation in this forum to this point. Most people arrive here seeking advice on the restoration, not modification, of classic speakers (AR in this case) or to offer experience in that regard. You pretty much started out by finding fault with the design of a pair of 2ax's, which apparently was your only experience with AR speakers. You installed a pair of new dome mids and pronounced them superior based on your years of critical listening. Was that meant to establish credibility with a forum comprised of AR speaker enthusiasts? "...I’ll finish this tweeter, then mount it for audition, and do some critical listening. I’ll compare it to the untouched unit. If it passes that test, I’ll have it tested with plotted results, mine and the original. I think that’s fair." Yup, in a Polk system. This will tell AR-4x owners how to modify the 4x crossover to work with the 4x woofer, woofer inductor, and extra large 4x tweeter capacitor....after they rebuild it. I'm sure everybody knows by now you have an engineering background. That and your audio hobby doesn't place you in a special category. Actual audio design engineers, including a former AR speaker engineer and other audio professionals have contributed much useful data and insight to this forum over the years. I'm sure you saw some of this in the SpeakerDave 4x replacement tweeter thread you cited. One prominent forum member actually owns the entire archive of AR engineering drawings and notes. Despite some of my comments, I am still interested, if not curious, as to how the tweeter turns out. I do agree that a softer suspension and increased excursion could bring it closer to the original. Roy
  10. I see this one is still going. 🙄 Bill, As I mentioned some posts ago in this thread I did mention that the 4x tweeter is "more compliant"...so in that regard, I agree with what you are trying to accomplish with the PRT tweeter. It rolls off more quickly than the original, yet is apparently more sensitive in the upper frequencies. The 4x's crossover exacerbates the issue. The result can be a subjectively aggressive character in the upper mid/lower high frequencies....most noticeable as the volume is increased. As I mentioned before, some people prefer this to the original character. Unlike what you seem to believe, I don't think its behavior as a drop-in replacement for the 4x tweeter is an indictment of the PRT tweeter as a whole. For the record, I did not add anything to the PRT's "surround". Some material was added to the paper cone to add some mass and try to reduce its upper mid sensitivity, which it did slightly...but I was fully aware that it was never going to make it sound the same as the original tweeter. Knowing that most people were accepting of the PRT tweeter, it was a simple attempt to make it a bit more friendly to my ear, and others who were not satisfied with it. It should be noted that the original tweeter had a similar treatment to the cone's perimeter, which is where I got the idea. Attached is a photo of a nasty old specimen showing where it was applied. Most 4x tweeters had various amounts of it on the cone. It should also be noted that the 4x tweeter has a larger cone along with the softer suspension. Your modifications to the tweeter appear to be thoughtful and neatly done, and I'll be interested in the outcome if they are practical for others to implement or acquire should they prove effective. "What I failed to effectively communicate to RoyC is that if these sound good in my Polks, they’ll also sound good in the 4X, or in any speaker, regardless of the crossover." You haven't failed to "communicate" anything to me. You just haven't convinced me. Roy
  11. Imo, wood glue is a very poor choice for this application. E-6000, Goop, or Gorilla Clear Grip (or some other strong contact adhesive) would be a much better way to go.
  12. Both of them? Just wood glue? All of the KLH 5 boards I've seen were installed with screws and had foam gaskets under them...no glue at all. Roy
  13. I wouldn't be concerned about going to banana jacks as long as you are aware of the need for insulating gaskets to prevent a short through the metal terminal plate. They will also extend further out from the back of the cabinet (if that is something that matters to you). You could also just use inline banana jacks. #8 ring connectors, my preference, will also provide a secure connection and is an easier approach than installing banana jacks. Whatever method you use to connect your speaker wire, it is a good idea not to simply wrap it around the terminals.
  14. Any time. Sounds like you have everything under control. Keep us posted.
  15. Not being defensive or difficult, just thinking that believing impedance matching resistors and your ears are all you need to make the tweeter compatible with two completely different speakers is naive. If nothing else it will be interesting. I think this thread has been sufficiently hijacked with this conversation at this point.
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