RoyC
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Posts posted by RoyC
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3 hours ago, giovanni56 said:
Those tables give capacitance and inductance values that are derived as if the drivers were pure resistors, in reality the drivers have a resistive and reactive component that varies (by a lot, especially at the Fs of the component), depending on the frequency, so they give a very rough indication with respect to the correct values for making a proper crossover.
Very true...tables will only provide some general guidance. The mechanical properties of drivers are a huge variable.
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4 hours ago, frankmarsi said:
...Roy, are you stating these little domes are appropriate and usable, cause right now, it’s still unclear.
FM
Hey Frank,
These domes have actually been around for quite some time. The output is very strong primarily due to a very compliant cloth roll suspension. The results are more like the AR-11 tweeter or Midwest replacement tweeter than the original 3a type with the foam suspension. If you are looking to "build" a close replacement for the 3a/LST or 2ax/5/LST-2 type of tweeter this isn't it unless it is modified, or a crossover tweak similar to that used with the HiVi tweeter is implemented.
As always, these discussions are a mix of subjective impressions and many variables, so the above is not meant to criticize anybody's personal preference.
Roy
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7 hours ago, Andre_Db66 said:
In the event of 4R or 8R not being appropriate, one can always use resistors or inductors like the HiVi tweak.
That comment pertained only to the orange dome AR tweeter. The one you used is available in 4 and 8 ohms, and can be made to work well as a replacement for the smaller black dome AR tweeter.
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3 hours ago, frankmarsi said:
Roy, check again, the link I posted indicates 4 Ohms. I wouldn't be surprised that if asked, the vendor would use less winds and offer 2.5 Ohms or so.
If that dome was too soft, with a thin coating of an appropriate substance, it could be hardened. It may be worth a shot if some one is eager enough to do the foot work and research. If pursued, this could possibly become a new source and lead to endless possibilities.
FM
Oops, sorry Frank...for some reason I thought you were referring to the replacement for the low impedance orange dome used in the models I mentioned above.
Roy
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The original AR tweeter of this type used in the AR-3, 2a, and early 2ax has a very low impedance. DCR is below 2 ohms. The assembly in the listing is described as having an 8 ohm impedance.
Roy
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Deepest condolences, Ella. Steve's contributions were indispensable to the foundation and high standards of this forum.
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Nice find, Scottie.
"...both tweets measure 1.8 ohms. Because they're exact it makes me wonder if the DCR is affected because it's a part of the system when measurrd. is there any of validity to that?"
Your tweeters and mid voice coils measure properly. Uninstalled, the tweeters should be around 1.6 ohms, and the mids around 2.5 ohms. System interaction and oxidized aluminum leads can both affect measurements.
Roy
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1 hour ago, meta_noia_fot said:
...The lacquer on these cabinets is certainly going to complicate each step of this.
The finish appears to be similar to the AR-2 cabinets you are discussing in the AR section. It will be interesting to see what the wood guys recommend. There is no shortage of nasty old KLH cabinets out there.
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2 hours ago, meta_noia_fot said:
Sanded down today. This is walnut, right? I’m second-guessing myself.
It appears to be the typical walnut veneer. The varnish/lacquer type of finish of the earliest AR (and KLH) cabinets is more difficult to deal with than the later oil type. It is not unusual for it to become blotchy as it is sanded. The front trim piece is solid wood and will be easier to deal with.
It would be prudent to wait for Gene to weigh in before proceeding. I see he posted as I was typing. Edit: and so did you.
Roy
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11 hours ago, RacerX said:
Ok, This sentence I didn't quite understand. I thought you meant that since I was using the original woofers that I would also need an inductor in series with that. My mistake.
Does this diagram look right?
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
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5 hours ago, RacerX said:
Thanks so much for replying. I bought the components with the speakers, and I hope they are the right ones.
As far as the inductor goes, I should probably try it with, and without. Would you know the specs for one to try?
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.
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17 hours ago, meta_noia_fot said:
Finished these up tonight. The silver cap was actually an Industrial Condenser Corp. cap. Those two 100 mfd caps measured 148 and 126, so I replaced them.
Good call...The large Industrial Condenser caps can be mistaken for Spragues, but seldom measure as well.
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On 3/24/2024 at 3:22 PM, RacerX said:
Anybody care to take a shot at a diagram? Its a shame that Carl spent his time designing this, but it wasn't fully explained. I'm not an electronics guy, and don't want to short anything out by guessing.
-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
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20 minutes ago, genek said:
The question is whether you are trying to improve the PRT by making it sound like the original AR tweeter or to make it sound "better" than the original.
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.
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5 hours ago, ReliaBill Engineer said:
How much easier would SpeakerDave’s crossover have been if the response anomaly wasn’t there? That’s all I’m saying. And what if the PRT sounded more like the original AR tweeter?
I certainly understand the “If it ain’t broke, don’t fix it!” proverb. But to me, it’s “broke”.
I thought you might encourage the attempt. Guess not.
So is the following an attempt to shame me somehow?? Reaching over the fence to get some type of agreement or “consensus”? Is that what we do in here?
“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 wentto the Parts Express website. Here is the description:”
And the above doesn’t agree with the below very well:
”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 ofanyone who implemented any of the suggestions.”
Selling “lots of them” doesn’t mean it’s the better option. It means it’s a convenient, “viable” option. Looking at prices of AR-4x pairs with the PRTs installed seems to drop the asking price considerably. Of course, it means the pair isn’t all original; and there are plenty of comments about the PRT being a compromise.
But I see no reason for my attempts to be disparaged, any more than SpeakerDave’s work to be.
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.
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On 3/19/2024 at 10:27 AM, ReliaBill Engineer said:
I think you’re being a bit too defensive, RoyC.
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).
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5 hours ago, jnolan5784 said:
Wondering about the utility of rebuilding the midranges of my 3a and LST. In my 3a's, the tweeters were working "fine" but I had them rebuilt on the recommendation of this forum and couldn't believe the difference it made. Just wondering about the midranges since I see that service is available from vintage AR. 10 midranges from a pair of 3a's and LST's would be an investment. Thanks to everyone.
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
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11 hours ago, ReliaBill Engineer said:
"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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11 hours ago, ReliaBill Engineer said:
There’s more going on in this tweeter than you realize.
First, RoyC said this PRT has a sound similar to the 4x AR tweeter, but some find it more harsh.
Thats why RoyC’s attempt to tame this PRT failed. He added his dope to the existing dope. Adding dope to a surround that is already too stiff won’t accomplish anything.
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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7 hours ago, meta_noia_fot said:
Is there anything I can do to cease the vibration? If I pull the crossover and backplate out again, is there something—some material—I can add to the seal there that would make a difference?
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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2 hours ago, RHollingsworth3 said:
Much obliged. Glad to be back here, and thanks again to Kent for the assist.
Has anyone that you know of replaced the stock terminals on the Seventeen with banana jacks?
I've done so with my 4311s and my Advent/1s, but I'm reluctant here because (1) there is the special challenge of the metal back plate and (2) it seems maybe a little like heresy.
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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1 hour ago, ReliaBill Engineer said:
“I bought 2 of the 8 ohm PRTs to play around with. I don’t know if I’ll have any more luck than you did smoothing them out. But it will be a fun learning experience.
I’ll test them using my Polk speakers, since it’ll be easy to adjust the mounting, and I have impedance adjusting resisters, and I’m very familiar with the original sound of these Polks. Also, the efficiency matches as well as useable FR.”
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.
Anyone see these?
in Acoustic Research
Posted
.1mh would be a good starting point.