ReliaBill Engineer

The treated silk suspension: RoyC said this in a thread over in the AR section: ” 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.” This is exactly why I gave the PRT a different suspension. The stock PRT cone outer edge is tightly secured to the phenolic ring. There is little chance for the cone to have “excursion”. To handle lower frequencies, 800 Hz-2000 Hz, the cone has to have much better excursion than above 2000 Hz. But that excursion has to be controlled, hence my use of butyl rubber treated silk. So now it has a damped, more compliant suspension. More like the original AR tweeter in that respect. In my opinion, it now has a “chance” to have a smooth roll off at the 4x crossover point of 1200 Hz

Besides seeming like the “right thing to do”, I added the wool felt and wool fibers under the cone for this reason: Fiberglass batting under the original AR tweeter cone. (borrowed pic) The original tweeter has AR’s “trademark” use of fiberglass damping pads. They used it a lot, and often, on their early mids and tweets. I chose wool. I’ve found over the years that it works well. (NASA uses melamine foam in large panels to absorbs sound vibrations.)

I have that scheduled. As I said earlier, I have a friend across town with the test equipment. He repairs amps, speakers, cassette decks and R2R tape decks. Not a tech shop, he works from his home. He’s known in the state for doing good work. He’s retired, so does it on the side. That’s also why I haven’t molested the 2nd PRT. I was his maintenance manager when we both worked for Goodyear. He was an excellent troubleshooter. I used to park him at a troublesome machine for half of a 12-hour shift, to document problems, mechanical and electrical. He would come up with a troubleshooting list that was nearly always correct. As an added feature, once I know what’s going on with the pair of 4x speakers I bought, if the tweeters work, I can test those too. Currently, I’m not aware of anyone who has measured/plotted the response of the PRT, despite it being sold as a replacement for the 4x tweeter.

The 4x has a lower crossover point than the 2ax. 1200-1400 Hz vs 2000 Hz for the early 2ax. So it should be interesting to see how this modified PRT responds. The 8” AR woofer of the 4x should be more capable of response up to 2000 Hz than the 10” of the 2ax. But that’s not what AR chose. 1200 Hz is a low crossover point for a paper cone tweeter. The paper cone tweeter has a free air resonance only slightly lower than 1200 Hz. SpeakerDave went to a 3rd order network to try to tame the tweeter hump close to its resonance. If I have the same issues, I’ll raise the crossover point to 2000-2500 Hz for both the woofer and tweeter. That way I can keep the first order network.

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.

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%.

YouTube sound clip. AR tweeter turned off, AR mid-tweet disconnected. Mid-tweet pot at 75% going to the modified PRT from the mid-tweet crossover. Mono signal from the Emmylou Harris record. Shure V15-III cartridge with original nude elliptical stylus; known for it’s excellent detail and balanced, flat response.

After listening to this modified tweeter, is it worth the effort? I’ve played 8 of my favorite LPs, and changed out cartridges 5 times. I can clearly hear the differences between the cartridges, which is as it should be. I put on the ADC 10E MKIV, ADC XLM MKIII, Shure V15-III and V15V-MR, and Pickering V-15 with the nude elliptical stylus. Each makes its own fingerprint to the music; each was clearly differentiated through this combination of AR woofer and this tweeter. None of them sounded harsh or strident. Nice amount of “”air” and a more musically effortless sound. The cartridges sounded good, the music sounded good. The stock PRT sounds “thin”, strained. Relatively “tinny” in comparison. On cymbals, blurred, not really clear and focused. Without sophisticated test equipment, all I can give are my subjective impressions at the moment. But we all know that graphs don’t tell us how something “sounds”, either. So “yes!”, I like the sound of this tweeter. It no longer has the sound of a “cheap” $17 paper cone tweeter. So yes, I think it was worth the effort on this. Now I need to hear the original AR tweeter. Hear for myself how different they are, or possibly alike they are. Anecdotally, my wife had a comment. I kept the modified PRT in the left speaker, switched back to my AR drivers in the right speaker. Went back to stereo listening. Her off-hand comment was, “Why all the work? I don’t hear a difference now.”

Ok. Good to know. Thanks! But I didn’t load photos on the AR section of my last post. I noticed no comments, but quite a few views in here. Guess I’m being stalked….

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.

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.

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.

The thin butyl sealant is fully cured. Pushing in on the dust cap of the cone, the surround is flexible and moves evenly all around the cone edge. Now to mount these in a pair of 4x speakers. But I’ll need to get the original 4x speakers working fully. The pots are corroded. Fortunately, I have spare parts from my 2ax refurb; 2 new pots and some metal film polypropylene capacitors. I will be able to listen to the original tweeters, then compare original to the stock PRTs, original tweeters to my modified PRT, and stock PRT to modified PRT. If all goes well, I’ll take these over to a friend for some measurements of impedance curves and FR plots.

Letting the sealant cure.

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

Too much pushback in here, for either approach or reason.

Instead of a butyl “roll” edge, I’m trying a treated edge. High quality, high thread count silk. Treated with butyl rubber. High flexibility but sealed and damped. I used parchment paper so the treated silk just pulls off after fully curing. Later I’ll cut what I need for the tweeter. Silk is bad about fraying; treating it first will allow me to cut it without fraying. The 2 rods were used to keep the parchment paper flat. It wants to curl.

I already started a thread in Mods and Tweaks yesterday. I guess you didn’t see it. I never said I was setting out to “improve an original” tweeter. Where did that come from?? I said I was working on improving the PRT. Go back and read my posts and see the pics. Nowhere do I show or comment about improving an original AR 4x tweeter! SMH

Nothing defensive in my post at all. Just me scratching my head at your very negative comments.

I started with a butyl rubber roll edge. But it turned out to be too stiff: So I removed it. Now I’m working on a different surround. It’s curing as we speak. It should be more flexible, yet damp well.

The new PRT: After removing the factory surround. I decided to add some acoustic damping under the cone, to attenuate the back wave. Black wool felt and a little wool fiber: After the felt is installed:

In rough shape, but intact: These will be my baselines for comparative listening. After some refurb, of course.

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.

I decide to move my efforts over to the Mods and Tweaks section. I would hate to fail and keep posting in here. Plus, it really doesn’t belong here.

I decided it would be best to discuss this in here, rather than in the Acoustic Research section. This way it can be seen without potentially hijacking a thread, nor competing with genuine original AR tweeter discussions. In essence, when the original 4x tweeters blow, or are otherwise damaged and non-functional, many replace them with the Phenolic Ring Tweeter (PRT) sold in various outlets such as Parts Express, eBay vendors, Amazon, etc. However, while the PRT fits nicely, and is cost effective (around $20), it doesn’t perform the same as the original AR tweeter. The small AR-4x speaker is a nice sounding legacy speaker, despite its small size. A common failure in these is the tweeter. Out of pure curiosity I decided to buy a pair of these PRTs and have a look at them. They are reasonably well made. But a bit “harsh” in my opinion. Can these be made to be better sounding? Can they more closely mimic the performance of a genuine AR-4x tweeter? That’s what I want to find out. I may fail or succeed. Original 4x tweeter: PRT, stock: Typical listing: