genek

What was new and different about Vilchur's invention was that he applied WDRC to multiple channels based on volume and frequency, with different levels set according to the patient's hearing tests, so that wearers got more amplification for sound levels and frequencies they had more difficulty hearing and less for levels and frequencies they didn't need as much help with. Prior to that, hearing aids applied the same level of amplification for all volume levels and frequencies and most patients either didn't get enough boost where they needed it or too much (sometimes painfully too much) where they didn't.

Who invented something is almost always defined, at least in popular memory, by who managed to get to a patent office first. Competing patent applications often win or lose based on subtle differences in how they describe similar tech. Prior to 1880, the US Patent Office required an actual working model be provided with all applications, and it was possible to build someone else's idea before they could and patent it, which is why you see a lot of old movies depicting characters working on "secret inventions" behind closed doors instead of the way things are done in real life today (file as soon as you think you can describe your idea and then begin development under "patent pending"). Edgar Villchur's biggest invention is arguably not a speaker at all, but the multichannel compression that is incorporated into almost every hearing aid in the world. When he developed it, instead of applying for a patent he published his work openly, putting it into the public domain. When asked about that, he would usually say it was too important a development in hearing research to limit and he didn't want to be involved in another patent boondoggle, but I wonder if he again didn't feel he needed the money that a patent might bring him and just wanted to ensure that this time he would be certain of getting the credit for his invention by publishing first.

IIRC, the difference between Villchur's sealed system and those earlier versions was that the prior art was done to reduce distortion at low frequencies while Villchur's intent was to extend those low frequencies to produce lower bass at low distortion from smaller cabinets, by making the woofer much much compliant. The prior versions were like some of today's subwoofers, which have sealed cabinets but are not acoustic suspension. Villchur's later recollection about his patent was that he made the mistake of writing it without professional assistance and failed to include explanations of how his acoustic suspension differed from prior art that were clear enough for a lay person to understand, and as a result the patent was successfully challenged in the first round. He chose not to appeal because at the time AR was already doing well enough for him based on its revenues without outside licensing income and he thought he had better things to do with his time and energy.

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.