RoyC
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"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
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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
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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.
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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
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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.
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Any time. Sounds like you have everything under control. Keep us posted.
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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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Suitable as a replacement in the 4x, not pair of Polks. No relevance.
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Hmmm, I'm sure it will be interesting, but it is hard to see how it will be relevant to the 4x. Impedance is only one parameter. You are proposing using it with a different woofer, different cabinet, different crossover...and conclusions reached based on your listening impressions?
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4 or 8 ohm. Are you installing them in 4x's? What kind of changes do you have in mind?
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Hi George, Based on your post, I'm sure you have plenty of sealant on the woofer and mid surrounds. As long as your woofer cones are returning more slowly. There is such a thing as applying too much sealant. The mids' surrounds only need one light application of sealant, which is much less necessary than the supplemental treatment of the woofer surrounds. It is more important to keep the mids' surrounds compliant. The most critical aspect of installing the mids is sealing their sub-enclosure from the rest of the cabinet. The mids originally had white foam gaskets in the space you filled with putty. There should be some kind of gasket material under the entire mounting flanges of all the drivers. Roy PS Great photos, Kent.
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The dust cap is original. I agree with Kent. It all looks good from here, including that fancypants capacitor arrangement! 🙂 Not sure of an any upside, but I'm certain they will do the job very well. Roy
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Good photo...I don't believe I have ever seen an original AR-9 woofer without the masonite ring. OP probably should post a photo if he is in doubt as to whether he has original or Tonegen replacements(s). It is important not to damage the ring if it is present.
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So you have experience using this tweeter in the 4x? What crossover and cabinet changes did you make to accommodate this tweeter?
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First of all, we are talking about subjective impressions of a 4x replacement tweeter based on feedback from users, not your opinion of the original AR tweeter. It should be noted that the replacement PRT type tweeter does not have the same construction as the original 4x tweeter...which has a more compliant suspension. The PRT replacement is not as capable in the mid frequencies primarily due to excursion differences. Despite this, a great many users are satisfied with it. It is the difference between this tweeter and the original AR-4x tweeter under discussion, not any flaws (or "distortion") associated with the overall use of this type of tweeter. Secondly, your conjecture as to why AR used dome tweeters is not accurate. It is not uncommon for speaker manufacturers to successfully use cone tweeters in 2-way designs. AR used dome tweeters for the highest frequencies in 3-way models to enhance dispersion and power handling, not because their cone drivers were distorting. Dome tweeters were used only in their more robust 3-way designs, never in their 2-way models. The cone tweeter used in 2-way models such as the AR-6, 7, 8, and 18 is still highly regarded. Obviously any driver used outside of its design parameters can "distort". In the end, we are probably talking about the same thing. We just have a different definition of "distortion".
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I disagree. No speaker system (or individual driver) has ruler flat frequency response...so are those departures considered to be "distortion"? The 4x replacement tweeter referred to as "harsh" by some people has been found to be satisfactory others. Earlier in this thread a forum member stated "I actually like the Parts Express replacements". Are you going to tell him he prefers "distortion"? If so, based on what? "Distortion" is usually considered to be something that should not be present such as noise, static, rattles. clipping, etc. I think you are actually referring to frequency response and tonal balance, not distortion. The crossover integrates presumably properly functioning drivers to produce a desired response. There will always be variations and preferences on the part of the designer and the listener.
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If it is Simply Speakers adhesive, the primary solvent is toluene. 12 inch woofers manufactured by Tonegen had a raised area stamped into the woofer basket instead of the masonite ring. Roy
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5w would be the minimum. 10w or higher would be better.
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As I mentioned above, the 4 ohm version is a better bet. If the mid range seems too forward, you can experiment by placing parallel resistance with the higher impedance replacement tweeter, starting at 8 ohms.
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It's not unusual for some old "vintage" amps to send very destructive DC to speakers when failing (at any volume level). It can't hurt to use a basic 2 to 3 amp fast blow fuse in an inline fuse holder as some protection insurance with these systems. https://www.parts-express.com/In-line-AGC-Fuse-Holder-070-609?quantity=1
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Agreed.
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Interestingly, back in the shop we also saw more fried woofer voice coils than tweeter voice coils...which had been protected by its crossover components.
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Not necessarily. In this case it probably has more to do with its inherent frequency response and behavior with the existing crossover.
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This tweeter is certainly not a perfect replacement, especially when used in a pair next to an original. Unfortunately, there are really no other "drop-in" options. There was some experimentation with crossover changes for this tweeter mentioned in the forum quite a few years ago, but I'm not aware of anyone who implemented any of the suggestions. Midwest is selling a 4 ohm version as well as the 8 ohm version sold by PE and Vintage_AR, and I'm more inclined to recommend that one if given a choice. https://www.midwestspeakerrepair.com/product/mw-audio-mt-4107-phenolic-cone-tweeter-2/ (Btw, VAR's addition of the sealant is just an attempt to calm the harsher nature of this tweeter...with very limited success.) Roy
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help needed with LST-2 and HiVi Q1R tweeters
RoyC replied to Andre_Db66's topic in Acoustic Research
I strongly agree with Aadams. Andre, You are over-thinking the possible issue at the moment. After verifying the problem is confined to the cabinet (which you have done), the very first thing to do is to simply place a jumper across the fuse. It will take you just a few minutes to do this. When the LST/LST-2 fuse becomes worn out it can pass a weak signal causing exactly what you describe. I have run across this several times. The issue is unique to these models. Roy