AR-4x Surprise

[swayzeeee]

A couple of years ago, I bought a pair of AR-4X's off a guy from Craigslist, having never heard any Acoustic speakers before but having heard plenty about their reputation. I stuck them in my office where they have been in service at moderate or lower volumes pretty much everyday. I thought they were ok. Nothing to get all that excited about really.

Recently, I've been thinking about re-caping them and was inspired a bit by the great AK post about restoring the pots, I decided to open them up and give them some care.

Well... what I found after prying off the grill of the first one just now was quite a surprise. The woofer is not at AR-4x woofer at all but an AR-7 woofer! And the tweeter? That's not the original, right? Grrrr. Well... what to do? Does anyone know about these parts? Is the AR-7 woofer very much different than an AR-4x woofer? As in, can they be interchanged? The tweeter appears to be a modern reproduction, probably this one from amazon: https://www.amazon.com/SS-Audio-Tweeter-Replacement-T-135/dp/B00F4FHR16

...And can this setup approach what an original AR-4x should sound like... or should I go searching for the real parts?

[JKent]

Welcome swayzeeee

Bummer. I'm thinking the biggest problem is probably the crossover. The 4x used a single 20uF wax cap and it has certainly drifted by now.

I doubt the woofer is a major problem but I could be mistaken. Maybe other members have a thought on that. The tweeter you linked is a phenolic ring that some (such as Simply Speakers and Vintage_AR)  sell as a replacement for the 4 series. I used them once for a 4xa restoration and they were not bad. The problem with the phenolic ring tweeter with the stock 4x crossover is they do not go as low as the original tweets.

Member ra.ra has experience with all iterations of the 4 series and may be able to better address the woofer issue and whether it might work to get a pair of 1-1/4" (AR-7 style) tweeters and rebuild the crossover as an AR-7 or a 4, 4x or 4xa.

Hope I haven't added to the confusion. Simplest solution IMHO would be to get a pair of 20uF caps and maybe a pair of L-pads (or clean the pots as you mentioned) and rebuild the crossovers, then see what you think.

Pics below show a 4x crossover with original pot and a 4x with L-pad. Note you don't have to remove the original cap. Also, the terminals on the L-pad on the L-pad are different. This is shown in the 3rd pic.

-Kent

 

[ra.ra]

13 hours ago, swayzeeee said:

Well... what I found after prying off the grill of the first one just now was quite a surprise. The woofer is not at AR-4x woofer at all but an AR-7 woofer! And the tweeter? That's not the original, right? Grrrr. Well... what to do?

Welcome aboard, swayzeee. The best way for you to get some specific feedback on your situation will be to post a few pics of what you've found, particularly the woofer and tweeter (front and rear) and perhaps the inner circuitry, too. Without pics, we're all just guessing at possible diagnoses and/or solutions. For posting pics, a simple JPG file of up to 100KB works best - - just drop and drag file to paperclip icon shown in window when you reply.

13 hours ago, swayzeeee said:

.....they have been in service at moderate or lower volumes pretty much everyday. I thought they were ok. Nothing to get all that excited about really.

This pretty much describes my own situation before I learned they could be brought back to life with proper servicing of a few components. Have faith......

[swayzeeee]

Thanks for the input so far. I've taken the stuffing out to get a look at the crossover. Looks like the 20uF cap has been replaced and the pot has been bypassed. No wonder the pot didn't work. ? As far as I can tell, the crossover looks like what should be in a 4x, once I clean up the pot and hook it up. I just have no idea if this crossover design is appropriate for the AR-7 woofer and replacement tweeter that I have. Maybe, I should start to look around for the proper woofer...

Pictures below...   

[ra.ra]

Wow, this is indeed a curious mash-up of parts  - - - I think the crossover experts need to show up to solve this puzzle.  One more question: what are the serial numbers on the cabinets?

The woofer looks like a perfectly good and very nice original AR-7 part. This woofer was always used in small volume cabinets, but I don't think it was ever connected to a coil.

As JKent has noted, the tweeter is a phenolic ring tweeter. There are several varieties of this type of driver, and it has been documented to sometimes be a suitable replacement for the AR-4x, mostly because it is a decent driver and a perfect drop-in fit. I do not know what the appropriate cap value might be when using a tweeter of this type.  

The pot control is original, and as you've noted, it appears to have been bypassed. Am unable tell from your pic about the cabinet stuffing - - original or not?

The most peculiar thing is that original coil and wax block assembly. With the 265 coil turns, I suspect your speakers began their life as the odd version of 4x which had two capacitors - - my guess is that wax block is a combination 20uF and 24uF cap. Also, it's interesting to note that the metal strap across the cap serves as part of the woofer circuit - - when you look closely, you'll find that the the coil is connected to one strap rivet while the blue woofer wire is connected to the other strap rivet. If you'd like to see this version of AR-4x schematic, I could post it here - - - but without either of the correct original drivers, I don't think it would be of much help with this project. 

 

[ra.ra]

FWIW.......pic attached shows dis-assembled AR-4x crossover that used 265 coil and dual cap - - - note three wires extending from wax cap.

[RoyC]

I agree with all of ra.ra's comments.

The fact of the matter is you only have partial 4x crossovers, and no 4x drivers. Even if your woofers were original, the replacement tweeters would not sound like the original tweeters, especially when used with the 20uf capacitor.

One possible project would be to continue to use the well regarded AR-7 woofers, and pair them with later AR tweeters used in the AR-6, 7 (and many later models). You could use them with a simple crossover consisting only of a 5uf or 6uf capacitor and L-pad, and end up with something very close to a number of nice  2-way models sold by AR from the mid 70's through the early 80's. The most difficult work would be to change the cabinet tweeter holes for the later tweeters.

Roy

[swayzeeee]

Oh boy. What about trying to acquire original AR-4x woofers and tweeters somewhere? I have AR-7 parts to trade! ? Seriously, are the original parts hard to come by? Just asking about availability/scarcity. I quick eBay search turned up one woofer that was crazy expensive and no tweeters at all. I'd rather wait, look around for the right stuff and see these restored properly than try to mash something else up. 

To answer ra.ra's questions: the serial numbers are FX46064 and FX 46081. I've never seen the original cabinet stuffing myself but judging from pictures I've seen posted, I think what I have is not original. There's no shroud to protect the woofer and the stuffing is more like fiberglass insulation than "rock wool".  

[ra.ra]

3 hours ago, swayzeeee said:

...the serial numbers are FX46064 and FX 46081...

Thx for confirming this, and it pretty much jibes with my suspicions. The "oddball" 4x assemblies (meaning two-cap version with 265 coil) I've seen have had serial numbers in the 30,000 to ±44,000 range (my pair are 38K), and your pair extends this range a bit further.

3 hours ago, swayzeeee said:

...the original cabinet stuffing .... I think what I have is not original....

I'm no expert here, but occasionally I've found it difficult to ascertain between rockwool and early fiberglass - - - both are itchy and scratchy to handle, and they each have that dingy yellow-grey-tan appearance. I've also encountered much lighter-colored fiberglass (yellow!), but the small glimpse of your stuffing almost looks like white poly fiberfill.

3 hours ago, RoyC said:

...continue to use the well regarded AR-7 woofers, and pair them with later AR tweeters used in the AR-6, 7 (and many later models). You could use them with a simple crossover consisting only of a 5uf or 6uf capacitor.....

This might be more complex or involved than a new member may wish to dive into, but it is very similar to a thought I was having today as well. This approach would probably require abandoning the woofer coil altogether, and the tweeter cap value may require some trial-and-error tweaking - - - I say this because the AR-4xa and several versions of AR-6 used a 10uF cap with the 1-1/4" tweeter.

Attached is a (blurry) pic of an AR 1-1/4" tweeter (used in many models) fitted into an adapter plate so that I could use it to transform a pair of AR-4x's (with one dead tweeter ) into a pair of AR-4xa's, concurrent with change of cap value from 20uF to 10uF.  

[JKent]

6 hours ago, swayzeeee said:

Oh boy. What about trying to acquire original AR-4x woofers and tweeters somewhere? I have AR-7 parts to trade! ? Seriously, are the original parts hard to come by? Just asking about availability/scarcity. I quick eBay search turned up one woofer that was crazy expensive and no tweeters at all. I'd rather wait, look around for the right stuff and see these restored properly than try to mash something else up. 

Roy's recommendation is sound . In fact it's what I suggested in my 1st response--get AR-7 tweeters and rebuild the crossovers to AR-7 specs. But yes--if you take your time and are patient you may well be able to find AR-4x woofers and tweeters and rebuld these as true AR-4x's.  If you look at completed sales on ebay, the woofs have sold for anywhere from $50/PAIR to $89 each so prices are all over the map. 4x tweeters went for $20 - 35 each. You could sell the AR-7 woofers. They were used in a few models so there should be a demand. In fact I don't see any on ebay so they may fetch a good price. The used PR tweets aren't worth much (maybe $12 - 15 each) but you could sell them too. Also try the For Sale/Wanted section here on CSP (it's free).

Then there are the coils. The 265 turn coil is bigger than the #5 (225-1/2 turns, 1.187mH) so you can just unwind them. OR get ra.ra to tell you how to wire up that "oddball" 4x crossover with the 265 inductor, 20uF and 24uF caps. Looks like you already have the 20uF film caps in there (so my original thought about the wax cap drifting was obviously incorrect).

Now just to throw you another curve: Instead of buying AR-4x woofers and tweeters, you could buy Avid 100 woofers and tweeters. They are drop-in replacements and some believe they are superior. The problem with the Avid 100 was its gawd-awful "woodgrain vinyl" finish. RoyC is responsible for this mod. I built them myself with his guidance and they came out very nice indeed. Take a look at this thread: 

 

[swayzeeee]

Thanks again for all of the suggestions and advice. I really appreciate it.

I think my strategy will be to be patient and look around for original 4x parts and then to sell the mismatched parts that I have. It might not even take that long... I picked up one woofer from eBay for under $50, including shipping this morning. 

ra.ra - would you be able to post a schematic for this crossover with dual caps? Or point me to where I might find one.

In the meantime, I've moved a pair of Ohm Model L's into my office, so I'm not exactly hurting for sound. ? 

...And maybe something else rally cool has come out of this... I was telling my uncle the story of my ARs last night over beers and he let me know that he has an old pair of KLH's in his attic that "don't work" and if I want to tinker around with them, I can have them. ?  Headed over right now. Coming soon to the KLH forum...

[swayzeeee]

Oh...The speakers I picked up were KLH Model Sevens by the way. Nice cosmetic shape, woofers sound strong but the tweeters are barely audible and sound kinda scratchy. An exciting find though! Now to start researching...no idea how to get inside them. I'll start another thread for that in the KLH section...

[JKent]

Great!

The Sevens are bigger versions of the Model Six. They have 2 tweeters per cabinet and are designed to sit on the floor. Very highly regarded and much more speaker than the AR-4x. Here's one thread: http://www.classicspeakerpages.net/IP.Board/index.php?/topic/4646-the-klh-model-seven-7/

KLH used notoriously unreliable Callins PVC capacitors, so that's probably where the problem is. Unfortunately, Henry Kloss had the ridiculous idea of epoxying all of the drivers and mounting the grille permanently. He did this with early Sixes and, I think, Fours. The only way to get inside is to cut a hole in the back panel or maybe (I haven't seen these) you can get in by removing the metal plate where the speaker connectors are. In any case, it will be a PITA.

See you in the KLH section! You're hooked now.

[ra.ra]

The thread attached describes the experience I had with the unusual version of AR-4x, where I received advice and assistance from the two members (and others) contributing here thusfar. 

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/7798-ar-4x-unfamiliar-crossover/&

Also, per your request I've attached my scribbled schematic for that project, and a decent pic of the woofers used in that version. These are the woofers from the earlier AR-4 model (only one year of production), and this particular crossover must've been designed in order to use up surplus AR-4 woofers while still matching performance specs of the newer and very popular AR-4x. Because locating a good pair of these rare 8-inch woofers would be painfully difficult, I would advise not to try to re-create this "odd" configuration of 4x speaker.

Instead, if you have decided to re-create the 4x, you should aim for a more typical version and be aware that there were several versions of woofers used - - - they all have round stamped baskets, alnico slug magnets, and semi-transparent dust caps, but there were differences in cone colors and textures and even color of surround treatment - - conclusion: there are several "different-looking" woofers that are nonetheless fully original. This is just meant to be helpful as you go shopping.

I believe each of these woofers was intended to perform similarly, but this may be incorrect because I know there were two different coils used throughout the life of the 4x; similarly, two different stuffing quantities. Hopefully other members can clarify these details.

Regarding tweeters, will you be seeking original 4x replacements or using the PRT tweets you already have? 

[RoyC]

5 hours ago, ra.ra said:

Because locating a good pair of these rare 8-inch woofers would be painfully difficult, I would advise not to try to re-create this "odd" configuration of 4x speaker.

Instead, if you have decided to re-create the 4x, you should aim for a more typical version and be aware that there were several versions of woofers used - - - they all have round stamped baskets, alnico slug magnets, and semi-transparent dust caps, but there were differences in cone colors and textures and even color of surround treatment - - conclusion: there are several "different-looking" woofers that are nonetheless fully original. This is just meant to be helpful as you go shopping.

I agree, ra.ra...

swayzeeee, the most common 4x crossover would consist of an AR#5/1.21mh coil (not the one shown in your photo), and the 20uf cap for (only) the original tweeters. While shopping for original woofers be careful to examine the condition of the cloth surrounds. Many have been ruined by being stiffened with various materials in heavy handed attempts to "seal" them, and periodically show up on Ebay. The 4x woofer surrounds should be very compliant.

Roy

[swayzeeee]

So... let me see if I'm following all of this. I have a rather early crossover in my cabinets with a 265 turn coil. (How does one convert from "turns" to Henrys, by the way?) That inductor was used as a special case early on to pair with surplus AR-4 woofers that they were using up. It's much easier to find AR-4x woofers, so I should build a crossover that pairs with those. 

To build the more standard AR-4x crossover, I will need an  AR#5/1.21mh coil and a 20uF capacitor. The cap is easy to find. How about the inductor? Would any 1.21mH inductor work or is there something special about the AR#5?

[JKent]

I think you're on the right path and your understanding of all this is correct.

I don't know how to convert "turns to Henrys" but you could unwind your inductor if you have access to an LCR meter (you just need the L part).

I had written that the #5 is 225-1/2 turns, 1.187mH. I got that from a chart (attached below) supplied by Tom Tyson. So I'm uncertain. If anyone asked, I'd say Roy and Tom were the top authorities on this but what do you do when they provide conflicting information? I hope they will chime in on this.

But yes--you could use any inductor, sort of. I believe the AR inductors are 17AWG  and therefore I believe you would be safe using an air core inductor of about that wire gauge and inductance. So maybe this one https://www.parts-express.com/jantzen-audio-12mh-15-awg-air-core-inductor-crossover-coil--255-424  or this one https://www.parts-express.com/jantzen-audio-12mh-18-awg-air-core-inductor-crossover-coil--255-254 But why spend $23 - 35 on a couple of coils? 

If you can't borrow an LCR meter there are some surprisingly useful ones on ebay for under 10 bucks. Or get a good one if you plan on doing more restorations. Using leads with alligator clips, clamp one lead to one end of the inductor coil and the other to a razor blade. Unwind some of the coil (just guess at how much. Maybe a dozen turns to start) and use the razor blade to slice through just a little of the varnish insulation on the wire. You should get a reading. Continue until you get the correct reading then cut the wire, leaving enough of a straight usable lead to connect it to the crossover circuit. Remember to sand the wire bare on the cut end.

AR-COIL specs_002.pdf

[ra.ra]

Yes, your description summarizes the analysis portion of our discussion pretty well. The parts-required portion of the discussion is based on your decision to re-create "original" AR-4x's rather than the other option suggested by Roy which would employ the AR-7 woofers and a simpler crossover.

Since you have decided to pursue the 4x route - - yes, 20uF caps should not be a problem to find, but aren't those new-ish poly caps shown in your crossover photo? What is their brand and value, and can they be re-used? And what about the tweeters - - are you planning to acquire used AR originals or use your existing phenolic ring tweeters? And before you go to place a parts order, I'd suggest that first you dis-assemble and inspect the pot controls to determine if they can be salvaged or require replacement.   

Regarding AR coils, I often use the same chart that JKent included for reference, but the 265 coil has never been listed, which leads me to believe it was unique to this odd 4x version. I never did measure its mH value, but the entire coil spool weighed in at 11.1 ounces. 

[RoyC]

1 hour ago, ra.ra said:

Regarding AR coils, I often use the same chart that JKent included for reference, but the 265 coil has never been listed, which leads me to believe it was unique to this odd 4x version. I never did measure its mH value, but the entire coil spool weighed in at 11.1 ounces. 

First, apologies for any confusion regarding AR's #5 coil value. The official spec is indeed 1.187mh. I mistakenly used a measurement I had written on a #5 coil in my AR coil stash. These coils typically measure from 1.17mh to a bit over 1.2mh. The variations are insignificant. As mentioned above, AR coils are comprised of a rather unique 17 gauge wire, but the 18 gauge, 1.20mh coil in Kent's link above would certainly be close enough. (Wire gauge determines resistance of the coil, but the difference between 17 and 18 at 1.2mh is quite small.)

swayzeee,  The greater the number of turns, the higher the inductance, but the number of turns for a specific value varies with wire gauge (thickness). The 265 turn/17ga AR coil has never shown up on a chart, but it is probably around 1.5mh or 1.6mh. As Kent suggested above, you can unwind your original coils to the proper value using a meter. Alternatively, you could carefully unwind them 40 turns to make something close to the 225 1/2 turn #5 coil.

None of the above matters if you are not using original 4x drivers.

I do have original #5 coils and a single 4x woofer available. Send me a PM if interested. I suspect, however, finding decent original tweeters will be a greater challenge than anything else.

Roy

[JKent]

Roy,

Thanks for the clarification.

47 minutes ago, RoyC said:

finding decent original tweeters will be a greater challenge than anything else.

So, I know the phenolic ring tweeters are not the equal of original AR tweeters but if good AR-4x tweets are hard to find, given the fact that some retailers are selling PR tweets as direct replacements, can you suggest something swayzeeee might be able to do to make the speakers listenable with those tweets?

Kent

[RoyC]

Not really...Reducing the cap value to 10 or 12uf is worth trying, but there are different versions of these phenolic ring replacement tweeters available. I would go with the later AR tweeters and AR-7 woofers, as discussed above, before staying with those tweeters. It would have a better chance of success.

Roy

[ra.ra]

4 hours ago, RoyC said:

I suspect, however, finding decent original tweeters will be a greater challenge than anything else.

I was having the same thought, Roy. The 4x tweeter is a good driver, and they were produced in large quantity, but it's not often that they show up on the used market, and even then, they often require some additional attention (i.e. cone detaching from face plate) after 50 years of life before using them in a restoration project.

1 hour ago, RoyC said:

I would go with the later AR tweeters and AR-7 woofers...

This approach has some appeal to me, too - - probably because I think very highly of both of these AR drivers - -  plus the fact that the OP already owns the woofers and the crossover is relatively simple (no coil). The biggest challenge with this scheme, IMO, is creating the adapter plate for fitting the (newer and) smaller diameter tweeter to the 4x tweeter cabinet prep cut-out, which is why I provided a photo example of my own solution to this issue. 

I want to offer a third option here for consideration and comment or criticism, and that would be to create a pseudo AR-4, since the OP is already in the process of acquiring AR-4x alnico cloth woofers. The mesh covered tweeter from the AR-4 (or mid driver from AR-2ax, see attached pic) is far more available in the used market and at very reasonable prices - - - and it is a perfect drop-in fit. The remainder of the assembly would require: refurbished (or replaced) rotary tweeter control; the #5 inductor coil; and a new 6uF cap.     

 

[swayzeeee]

Just a quick update on this project. I'm proceeding with trying to restore this speakers with original parts based on the "normal" crossover wit the AR#5 coil. I have the coils, two woofers and one tweeter... still need to find one more tweeter somewhere.

While I'm waiting for one to turn up, I thought I would build these using the parts that I have now. It might be cool actually to compare a "real" AR-4x tweeter side by side against the modern replacement phenolic ring tweeter, no?. So, I cleaned the pots, built the crossovers with the #5 coils and sealed up the cabinets following the instructions in the potentiometer restoration guide on AK.

Both speakers are up an running now. Guess what? Yeah... the AR tweeter sounds a lot better. There's really a clear difference in clarity and precision. The replacements are noticeably louder, but that's not necessarily a virtue. I guess they'll do in a pinch. They're not awful but...now that I've heard the real thing there's no going back!     

[swayzeeee]

Finally scored a second tweeter! It's installed and my AR-4x's are complete and restored to original. They sound great too!!! Thanks again to everyone here for all the help!