genek

Check eBay. Sellers there seem to come and go.

It does sound like rock wool, and I think I can see crumbly bits that you don't expect to find in fiberglass.

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.

Is it actually rock wool (grey with little bits of, well, rock) or fiberglass?

There are repros available using ink on brass. If you're asking about embossed and paint-filled lettering, haven't seen any of that so far.

Sadly, the forums on this site are the closest thing there is to a repository for classic "East Coast sound" speakers. If we can ever get to update the libraries, there's a good 8-10 years worth of content that needs to be extracted from old forum posts.

You might not have noticed, but the site is a bit stale because its owner, who hosts it as a personal project rather than a business, hasn't had time to update it for a long while. And several of our long-time members who were the primary source of deeper technical content like measurements have sadly passed away. So you have to dig long and deep to find some of that stuff. In the name branded forums, the focus is on preservation and restoration, and discussions about changing drivers are focused on finding or creating "holy grails," new drivers that can be made to reproduce original sound. This forum is anything goes as far as changes go. But pretty much everywhere on the site, people will almost always want to know how something sounds and how it measures, because we're a bunch of audio nerds. Otherwise, we'd all just have home theater systems from BestBuy.

You actually need objective measurements and blind listening tests, because the single most powerful influence on listener preference is probably confirmation bias.

It isn't just about replacing the AR tweeter with another AR tweeter, or about replacing it with a different tweeter that replicates the sound of the original. Even a mod that is intended to alter the original sound can only be verified to be an improvement with objective measurements. Otherwise, you are in the same subjective territory as people who are convinced that their $5000 speaker cable sounds better than 14ga lamp cord.

The PRT is sold as a replacement driver. But the data that you discovered and posted (a valuable contribution to the site, btw) shows that it really is not a suitable replacement and never has been. Your project is quite interesting to follow. But in the absence of measurements, the finished result will have no more credibility that the stock PRT did before we saw the data you posted. Possibly even less, since you are still the only person who has posted a first hand listening impression.

The problem with YouTube vids, or any sort of uploaded audio file, is that what the listener hears is the original source (in this case, your modded tweeter) filtered through two other transducers (the mic and whatever speakers or head/ear phones the listener is using). And that's excluding any effects of the recording app, streaming compression, etc. This is why the majority of us put our faith in measurements. Preferably, comparative tests of mods and originals taken with calibrated equipment, though we know that most people doing mods and tweaks don't have access to an actual audio lab with an anechoic chamber.

I mix one part dye to three parts retarder. The usual instruction is 50/50, but I prefer to build color up much more gradually. This is especially important if your wood is cherry (we're still not sure), because stain on cherry can get blotchy if left on. Wipe it on and right off, don't leave it sitting there and soaking in. You'll get a very light tint that will darken slowly with repeated applications.

My preference is an NGR (non grain raising) dye stain. This is an alcohol-based aniline dye that doesn't obscure grain the way pigmented stains tend to do. I dilute the stain with reducer so it adds color lightly, then do multiple applications to get the color the way I want it. Once it fully dries, then it can be coated or oiled. Whether to coat or oil depends mostly on whether you want a gloss. Most of my refinishing these days is dye stain followed by a tung oil finish (tung oil and citrus-based solvent blend). You can also use dye stain to tint an oil finish, but you'll have less control over the color that way.

I thought one of the end faces looked a bit like pine, but AR-2s didn't come with unfinished short faces unless the entire cabinet was pine. The long faces are definitely not pine. The color of the wood under the flaking makes me think it's possible that it could be cherry. Those dark pockmarks on the left speaker in the last photo are also more common in cherry than walnut. If you're thinking of staining, I'd say just pick the color you prefer.

Can you shoot more faces? Ar-2s originally came with some unfinished pine faces.