Help me with my mismatched AR-4s

[commasense]

I have a pair of AR speakers that I bought from a previous owner sometime in the early or mid 1970s and used happily as my main stereo speakers for decades. For the last several years they have been out of service, replaced by a pair of JBL L80T's that I bought more than 15 years ago.

About a year ago, I hooked up the ARs for the first time in quite a while and discovered that the tweeter on one of them had blown (or so I thought). I ordered an original replacement from Vintage-AR, but I didn't have a pressing need to use the speakers, so I didn't get around to installing it. Then, a few weeks ago, my wife and I began the process of converting one of the bedrooms into a family room (she calls it my "man cave") and moved the JBLs there from the living room, along with the 65-inch Panasonic plasma TV, the Yamaha A/V receiver, surround speakers, etc. It's turned out very nicely.

So now that the ARs are needed in the living room, I finally got around to installing the replacement tweeter from Vintage-AR a few days ago (more than a full year after receiving it!). To my dismay, it didn't work. I assume (but have not tested) that it is good, and that my problem is elsewhere in the cabinet. I went online to research the problem, and quickly found this wonderful site. From my reading here, I'm guessing that the problem is most likely the pot.

As I read about the AR-4s here, I decided to try to determine the vintage of my pair from the serial numbers, and looking at the backs (they both still have both of their original labels), I was suprised to discover that one (the one with the "blown tweeter") is a 4, and the other is a 4x! All this time, I had had no idea they weren't completely identical! And I wonder how the person I bought them from happened to have this odd couple?

Here are the details: AR-4, s/n F 19401. AR-4x, s/n FX 85379.

So now I am considering what to do, and wanted this board's expert opinions on my options. I am not a purist about historical accuracy, and would rather have a sonically identical pair than retain the integrity of the AR-4.

My inclination is to refurblish both with new pots, crossovers, and modern replacement tweeters, and possibly install new surrounds on the woofers. This will leave me with two working (I hope!) original 3.5-inch AR-4 tweeters that I can sell. I may also see about dry cleaning the grill covers, as a member here has done. The casework is in good, if not glorious, condition, and in their installed location is barely visible, so I probably won't bother refinishing the exteriors unless I suddenly have a lot of unexpected time on my hands. (Yeah, right!)

What do you all think?

[JKent]

Welcome to the CSP!

A few thoughts, not in any particular order:

• not so sure about "dry cleaning" the cloth grilles. If you remove the cloth you'll never get it back on. Replacing the cloth is fairly simple--you can use real (not synthetic) linen purchased locally or use the 1-2-3 Stitch product mentioned in the AR-3a restoration booklet.
• You can spruce up the cabinets easily by using Howard Restor-a-Finish. It's sold in Home Depot and some hardware stores. Comes in Walnut. Wipe on/wipe off. If the cabinets are not too far gone this will make a big difference. You can then apply either Watco Danish Oil or wax them.
• LEAVE THE WOOFERS ALONE! They have cloth surrounds that will last forever (well, the 4 does. Most 4x's did too but if you have a foam surround it will need replacement).
• Test your original tweeter. The replacements sold by Vintage AR are not authentic but will do in a pinch.
• Pots can be replaced with inexpensive ($5) L-pads and will work perfectly.
• The capacitor should be replaced. You leave the original in place and snip the wires. Replace with a 20uF film cap (in the 4x--the 4 used a 6uF cap). There is a 4 schematic, photo and discussion here, (there is also a side-by-side photo of a 4 and 4x): http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7264

I've never worked on a 4 but some members here have so I'll let them comment on any modifications (to give you a matched pair). However, it's my understanding that the 4 is rare and collectible so you may not want to make major changes to it. ra.ra. may be the guy to ask.

Good luck and don't hesitate to ask questions or post pictures.

btw--another way to go: Buy a pair of Avid 100 speakers. Great speakers in awful cabinets. The woofer, tweeter and crossover are all perfect drop-in replacements for the AR-4x (so I assume they'll fit the 4 also). Then sell the 4 and 4x components. But as I said, the 4 is collectible if it's unmolested.

Kent

[rjr513]

For trying to clean your speaker grille cloth,one thing you can do is get a towel and spread out on a work table then lay your grille with cloth still attached on the towel,get you a spray bottle a mix household bleach with water 50/50 ratio and spray onto the grill saturating the clotch.Now the secret to not cuasing warpage to the grille frame is using the towel to soak up most of the solution leaving enough on the cloth to bleach the grill fabric.I had a set of old AR-LST side grilles so i said what heck let give it try attached are the results

[ra.ra]

Welcome indeed, commasense, and it's about time those AR's have earned a spot in your living room! As much as I love the sound from these old boxes, I have an equal appreciation for the simple and timeless visual aesthetic (walnut, linen) that they add to interior decor. Your query is well-timed - - - I just happened to be listening to my AR-4's (proudly on display in living room) when I read your post.

Not only do you have a mismatched "pair" of AR-4's, but as you've recently discovered, you also have a mismatched "pair" of 4x's! As far as the vintage of your speakers, the AR-4's were only manufactured for about a year, '64 to '65, I think, and then they became 4x's from '65 to '73 or so with changes to the tweeters and crossover circuitry.

JKent's reply is very good, and I was pleased to see that he referenced my recent post where I received some great help - - - most particularly the great (yet simple) original schematic spec sheet provided by Tom T. I am mostly curious about which type of 'original replacement' tweeter you have obtained which seems to not work. Not sure what's going on with your non-working tweets, but it's very possible that you are correct that the problem "is elsewhere in the cabinet". Maybe the pot? Maybe a wire? Maybe the cap? Do you have the capacity to test these so-called non-working drivers with an ohm meter or household battery?

Just another opinion here, but regarding JKent's comments:

* I read the post about dry cleaning grilles as well and was slightly amused yet intrigued. I've never tried this method, and would never have thought of it myself, but if it works as reported, it may be the ideal solution for cleaning the original linen. Personally, I'm always skeptical of dry cleaning in general, but this would sure beat taking the linen off the panel frame and soaking, drying, re-stapling, as others have tried.

* Cabinets. Agreed ...... at least a modicum of attention to the cabinet appearance will pay off in spades - after all, it's the living room! The Howard's products are remarkably easy and effective, and after a little oil and/or wax, you'll have some new attractive "furniture".

* Woofers. Agreed ....... I think the 4 series may have never used a foam surround until the 4xa, so yours should have cloth surrounds. If still intact, do not replace them. At most, a re-coating of liquid butyl (on the cloth only) might enhance performance.

* Tweets. Again, agreed. Test them, if possible, to decide if they "work".

* Pots. Good advice. Kent loves the L-pads, but I've always resurrected the old pots.

* Caps. More good advice. You can remove or leave the original wax block caps, but it's important to note that the AR-4 (6mf) and the AR-4x (20mf) employ different values of capacitor. For my own 4 series speakers, I've used Solen, Dayton and Erse - - - all reliable manufacturers of capacitors.

If you can determine that the 3.5" AR-4 (with metal grille) tweeters do in fact work adequately, I'd suggest you replace the caps accordingly and create a "pair" of AR-4's. Post some pics if you can and keep us informed of your thoughts and progress.

[commasense]

Thanks, all for the replies. My reasoning for making both speakers 4x's instead of 4's was that the 4x was reportedly an improvement over the 4, so why not upgrade one rather than downgrade the other? Am I wrong in thinking that? What is the sonic difference between the 4 and the 4x, assuming both are in ideal condition? (Of course, for most of the last 40 years, I've never perceived a difference between the two!)

What would the dollar value of an "unmolested" AR-4 be compared to one that had been converted to a 4x with a new tweeter? And if I leave the old tweeter (assuming it still works) but replace the pot and/or the cap, is it still "unmolested"?

How do you suggest I test the tweeters? I have an ohmmeter and certainly have ordinary batteries. (In case I wasn't clear, the one I got from Vintage-AR last year was an old-style 3.5-inch to match the AR-4, not a new replacement. I was planning on buying the Vintage-AR replacement tweeters if I upgraded both to 4x's.)

As for the caps, ra.ra, if I make the speakers the same, either both 4's or 4x's, the caps should be the same, too, right?

Finally, regarding the wood, it's in good shape, but the speakers are placed on top of a built-in bookshelf, next to the outer walls of the room, so the bottoms and one side of each are not visible at all, and they are surrounded by framed pictures which all but totally obscure the third side. And they are high enough up that most people shorter than your average NBA player won't see the tops, either. So only the surrounds on the front edge are visible, and they look fine. Although your suggestions for refinishing sound simple enough, what is visible of the cabinets doesn't warrant even that amount of effort at this time. The priority is getting a working, matched pair.

I look forward to your replies. Thanks again.

[commasense]

Why weren't the paragraph breaks in my last post preserved? The post looked fine in preview. Can I edit it to make it more readable?

[JKent]

If you look at the bottom of the post there is an "edit" button. So yes, you can edit the post. I'll let ra.ra. address the other issues since he has experience with both the 4 and 4x.

Kent

[commasense]

The formatting problem seems to have arisen from using my iPad and the mobile version of the site, which didn't take the return characters I originally put in. I've re-edited on my PC, and it's fine. Strange.

[ra.ra]

Commasense:

First of all, I don't know where you live, but I find it hard to believe you do not have NBA players to your house for listening sessions. After a tough loss or a thrilling victory, I often have the Celtics here to chill out with some Motown tunes, doo-wop or R&B. Rajon Rondo might not be able to see the tops of the speakers, but Kevin Garnett certainly can, which is why I keep them dusted, waxed, and looking good.

I totally understand your formatting problems. My first posts on this site ended up looking like Egyptian hieroglyphics.

My first serious comment regards my previous post: although my note represented my own personal experiences, I may have made a naive mis-statement about the woofer surrounds - - - my thinking was that foam surrounds were not introduced on the 8" woofs of the 4 series until the 4xa was introduced, but another recent post (with comment by Roy C, who knows this AR history far better than I) states that some late issue AR-4x's did have foam surrounds on the woofers ---- news to me!

Let me first expose my own situation and/or bias. I have four pairs of "4's" - - - 3 pairs of 4x's and one very early pair of 4's. They are all really great speakers, but sentimentality is involved here - - - my first 'real' audio speakers were 4x's purchased over 40 years ago. One of the tweets in this original pair has mysteriously died, so now I am in the process of converting this pair of speakers into 4xa's for two reasons: the tweet is dead so I have to do something; plus, I've been tremendously impressed with the output from the later version of 1-1/4" tweeters. So if/when I complete this transition, I'll have at least one pair of each version of the 4-series speakers.

Nonetheless, let's return to your ultimate objective: you want a "sonically identical pair" of speakers, which seems to me to be a very sensible goal for two channel output. You'll definitely need new caps for both, and at least one tweeter, but you actually have three, not two, options: create a "pair" of 4's, 4x's or 4xa's. If you are seeking the ultimate in AR engineering, some might argue that would come from the response of the 4xa's, which were supposedly an improvement on the very highly-touted and ground-breaking 4x's.

Having said that, here are my thoughts on 'value' and 'authenticity'. Because your two speakers have non-identical paper labels on the backside (one 4 and one 4x), they might never be seen as a collectible and original 'pair'. Still, you very well might be able to construct a virtual pair, sonically speaking. Because of their limited production, AR-4's are perceived as relatively 'rare'. AR-4x's, on the other hand, sort of revolutionized the industry with their success, and there were gazillions produced throughout AR's heyday. AR-4xa's, while possibly the best performing speaker of the three within the 4-series, were something of an afterthought and became lost amongst the marketing efforts of Acoustic Research with their newer models which featured the very same tweeter - - - the AR-6 and the AR-7.

The ultimate choice is certainly up to you, but I'd say that the expense and effort is pretty much equal between trying to create 4's or 4x's. If you decide to create the 4, the cap will be less $$$ but the tweet might be more $$$ (but it sounds like you've already got two tweets). I do switch back and forth all the time from my 4's and 4x's, and although my opinions differ sometimes depending on the program material, generally I could say that the 4x's extend into slightly higher frequencies, but the 4's have a more full and rich midrange that suits my taste for jazz music.

[mraudio]

I was wondering one thing over all. 40years old used capacitors are not reliable or are dead ones completely !!! 1st. must change to new ones and high quality ! Old AR tweeters are top quality still today ! That strange AR4 pair reminds me one case, friend was bought a AR6 pair and years later I was checking them and realised that tweeters was differents !!! Not the same type !? Personally, I love those old 1960´s and early 1970´s AR loudspeakers. Keep them original condition. Sadly, but I lost all my old AR sales leaflets and catalogs. If anyone have a any left for sale for me. I like to pay all the cost. Thanks!

[commasense]

Here are some questions from my post #5 that haven't been answered:

1. What are the sonic differences between the 4, 4x, and 4Xa, assuming all are in ideal condition?

2. How do you suggest I test the tweeters? I have an ohmmeter and certainly have ordinary batteries.

And some new questions:

Although I understand the function of crossovers, I've never gotten into the details of their inner workings.

3. If I want to make both speakers AR-4x's, do I have to replace other components of the crossover circuit in the 4 to make it a 4X, or just the capacitor?

4. If I have to replace other items, can someone point me to a schematic, parts list, and/or complete instructions on what to do?

5. The pot is the same for both models, right? So I can just get an L-pad from Parts Express?

Although I was pleased to find Vintage-AR on eBay, I get the sense he is not necessarily the best source for everything. For instance, I've learned here that the pots he sells are available for about a third his price at Parts Express.

6. If I want new 4x tweeters, is there another source for them? What about the gray sealant?

Thanks.

[JKent]

Here are a couple of answers:

• A simple tweeter test" Take a toilet paper tube or similar and use it as a stethoscope to isolate the tweeter's sound. The tweeter can get drowned out if you don't isolate it.
• Here is the 4x schematic: http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/ar-4x_schematic.html
• If you make both 4x the tweeters and all crossover components must match
• the pots are the same and the L-pads will do nicely
• There are no new 4x tweeters
• The sealant can be either Mortite rope putty or get a brick of "duct sealant" in the electrical department. Or--PartsExpress sells this gasketing tape http://www.parts-express.com/pe/showdetl.cfm?partnumber=260-540

ra.ra. and others should be able to answer your questions about comparing the sound and hopefully can provide a 4 schematic.

Kent

[commasense]

Kent,

Thanks for your quick reply.

• If you make both 4x the tweeters and all crossover components must match

I understand that, but are the other existing crossover components (aside from the cap) in the 4 different from the 4x? Do I need to replace all of them?

• There are no new 4x tweeters

Here is the new replacement tweeter Vintage-AR is offering for 4X's, and that I was considering putting in both speakers.

http://www.ebay.com/itm/ACOUSTIC-RESEARCH-NEW-AR-4X-REPLACEMENT-TWEETER-/160704487794?pt=Speakers_Subwoofers&hash=item256abbe172

Any thoughts?

[ar_pro]

I believe Parts Express has the same phenolic ring tweeter for $16.75:

http://www.parts-express.com/pe/showdetl.cfm?partnumber=270-252

PE offers it as a replacement for a number of manufacturers' originals, and there is a positive comment on its use in the AR-4x.

I've heard the phenolic tweeters that were used in the old Martin Magnificat systems, and they were surprisingly smooth - not up to the standard of an AR dome, but still very good.

[Steve F]

Differences between the 4, 4x, and 4xa:

The AR-4 was introduced in the 1964 time frame and used an 8” woofer with a treated cloth surround. The tweeter was a 3 ½” cone, covered with yellow fiberglass and a black metal mesh. Presumably the fiberglass covering was there to damp out some cone resonance or otherwise smooth out the sound, but AR never published any details about the fiberglass’s exact function.

At the time, this was the smallest iteration AR had ever done of its original acoustic suspension concept, and the 4 proved to be quite a nice-sounding small speaker, with clean, low-distortion bass down into the high-50’s Hz region and a natural, uncolored mid-treble response.

The original AR-2x was quite similar to the AR-4, in that it was a 2-way (but with a 10” woofer) that used the same 3 ½” tweeter. Both speakers crossed over at 2000 Hz.

The 3 ½” driver had a somewhat restricted dispersion characteristic and its upper FR limit only extended to the mid-teens kHz. You can see detailed response curves of this driver in the newer 2ax system curves published in the early ‘70’s. The 2ax used this driver as its midrange.

AR realized that the tweeter was holding back the 4’s true potential, so about a year after the 4’s introduction, AR came out with the AR-4x. This was a smash success, the speaker that totally “broke the rules” as far as what could be expected from a ‘small’ speaker. The 4x used a brand-new 2 ½” tweeter that had appreciably better dispersion characteristics and a more extended HF response—all the way out to 20 kHz, at least on axis. The 4x crossed over at 1200 Hz—pretty low and that tweeter has been known to get into a little trouble if pushed too hard.

(Likewise, AR updated the 2x to a ‘new’ 2x, which used the 2 ½” tweeter replacing the old 2x’s 3 ½” tweeter. The 2x also crossed over at 1200 Hz.)

Stereo Review, High Fidelity, Consumer Reports all showered big praise on the 4x and it was universally heralded as the best small speaker on the market, a reputation that it would hold pretty much until 1969 or 1970, when the Smaller Advent and AR-6 came on the scene.

The AR-6 used a brand-new 1 ¼” tweeter (they called it a 1 ½” at the time, but changed the designation to 1 ¼” later on) that had even better dispersion and response characteristics than the 4x’s 2 ½” unit. In fact, the AR-6’s tweeter was nearly (pretty close) a match for the ¾” dome in the AR-3a, -5, and -2ax. Early 6’s crossed over at 1500 Hz; later ones were 1800 Hz. Minor running changes to the woofer necessitated the crossover changes.

The AR-6 came out in mid-1971, if I recall. In fall 1972, AR introduced the AR-7, a smaller version of the AR-6, with an 8” woofer in a smaller cabinet and the same 1 ¼” tweeter. The 7 was a smash success in its own right, establishing a new level of performance for a compact speaker.

At this point, the 4x was becoming obsolete. It should have simply been discontinued, as the AR-6 and AR-7 had the 8” 2-way compact cabinet market covered very nicely. But AR was reluctant to let go of the “AR-4 etc.” franchise, so in 1973-4, they came out with the AR-4xa—priced and positioned between the 7 and the 6— which used essentially the same foam-surround woofer as the 7 in the very slightly larger 4-shaped cabinet, with the new 1 ¼” tweeter. The 4xa crossed over at 1600 Hz. It sounded fine, with the expected improvement in dispersion and openness that the 1 ¼” tweeter offered over the 4x’s 2 ½” unit.

However, the 4xa was totally unnecessary in the marketplace and it languished in near obscurity until being phased out with the intro of AR’s ADD series in 1975-77.

There you go: the definitive history of early AR 8” speakers.

Steve F.

[JKent]

are the other existing crossover components (aside from the cap) in the 4 different from the 4x? Do I need to replace all of them?

• There are no new 4x tweeters

Here is the new replacement tweeter Vintage-AR is offering for 4X's, and that I was considering putting in both speakers.

http://www.ebay.com/itm/ACOUSTIC-RESEARCH-NEW-AR-4X-REPLACEMENT-TWEETER-/160704487794?pt=Speakers_Subwoofers&hash=item256abbe172

I don't know what the AR-4 xo looks like. The xo is just a cap and a coil. If the coil is different that would have to be changed too.

The Vintage-AR tweeter is not a new AR-4x tweet. It's a phenolic ring tweeter from Parts Express with some of Roy's damping goop on it. You'll have to ask Roy how good it is, but it AIN'T original.

You may want to look at Carl's work with the PRT here: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7561#entry95332

Kent

[commasense]

I spent the weekend following through on my plan to upgrade my two speakers to become matching AR-4x's. I ordered two each of the phenolic ring tweeters, Dayton 20 uF capacitors, and L-pads from Parts Express, along with a roll of their speaker gasketing tape. (Throughout this post, I will refer to the individual speakers by their original designations -- the 4 and the 4x -- even though by the end both had become refurbished 4x's.)

The 4.

The 4x:

I started on Saturday afternoon with the AR-4 . Here is the interior of the 4 as I found it:

I simply replaced the three components (pot, L-pad, tweeter) with their new counterparts. Putting everything back together, and testing out the upgraded speaker against the untouched 4x, it sounded good.

Here is the original corroded pot that caused the tweeter on the 4 to stop working. I suppose I could have cleaned it up an continued using it, but I preferred the reliability of the L-pad.

On Sunday, I opened up the 4x and discovered to my dismay that the schematic for the 4x differs somewhat from that of the 4. I realized I'd have to redo the 4 if I wanted them to be precisely equivalent. I also observed signs that the 4x might have been worked on by a previous owner, and found that the wiring of my 4x differed from the schematic. Here is the original configuration of my 4x.

According to the schematic, the green wires from the cap and the tweeter should be connected to terminal 2 of the pot. On mine, the green wire from the cap was connected to pot term 1, and one side of the coil was attached to pot term 2 with the tweeter lead. I don't know how or why this was done, or what the functional effect was. All I can say is that the speaker always sounded fine to me.

So I wired up the new components in the 4x precisely according to the schematic, then did the same for the 4. Here's the rewired 4x:

And here's the re-rewired 4:

Here is the upgraded 4x exterior:

This is the upgraded 4 exterior before I reworked it on Sunday. (Because the tweeter leads in the 4x were so short, I had to mount the tweeter with its terminals oriented toward the woofer, as shown above. When I redid the 4, I turned the tweeter 90 degrees so it would visually match the 4x, but I didn't take a picture of it in that configuration.)

Here's the back of the 4 with the knob that came with the L-pad. It's a bit large, but it sure makes adjustments easier, especially when you're reaching behind from in front and can't see the thing.

Here they are in the living room: 4 on the left and 4x on the right. I think these pictures demonstrate why refinishing the cases, which aren't in terrible shape anyway, would be relatively pointless.

Here are the original tweeters, the 4's on the left and the 4x's on the right. Note that the yellow dots are on opposite sides. I suspect that this means that if I had left the 4 unchanged from my first rewiring it might have been out of phase with the woofer. I might have heard something like that in my brief check on Saturday, but I'm not sure.

I hadn't listened to these speakers in quite a long time before doing the work, much less done any serious evaluations or measurements, so I can't describe the differences in their sound after the refurb with any rigor or detail. But they sound great, as good as I have always felt they should sound, and I'm quite pleased with the results.

Finally, having completed all this work, I have the following components left over, if anyone is interested in purchasing them: two original AR-4 tweeters (one bought from Vintage-AR), one original AR-4x tweeter, and two original pots. The tweeters are all in fine working condition. PM me if you're interested.

[JKent]

Very nice!

A couple of thoughts:

• The AR4x used the #5 inductor coil, which is 225 1/2 turns, 1.187mH
• I don't know what the 4 used but yours is marked "200" so I assume it's a #4, with 200 1/2 turns, 0.880mH. You "could" add wire to that one to bring it up to 225 1/2 turns but if you don't hear any difference maybe not bother.
• I see what you mean about the placement but in that very nice room you may still want to just go over the wood with some Howard Restor-a-Finish or even just lemon oil
• If they were mine, I'd replace the grille cloth. Not difficult. The nicest is "lambswool" linen from 1-2-3 Stitch. It's kind of hefty so you have to be creful not to make too much bulk on the perimeter of the wood frame or you'll never get it back in the opening. I used that linen on my 4x's and it really looks nice
• Roy may comment here but I think some of his goo on the PRT may help (if you bought the tweets from PE. If you bought them from Vintage AR they already have the goo).

Enjoy the speakers! Hope you enjoyed the project.

Kent

[ra.ra]

Very nice step-by-step procedural explanation, and terrific pics to boot!

Re: aesthetics, my observation is that the grille cloths don't look too bad (I've seen far worse!), but I do agree that a little TLC to the cabinets always pays off - - - with a little fresh oil, the wood often seems to let out a near-audible sigh, and besides, for some of us it's the most instantly satisfying step with these restorations. How would you like to stay dry all these years and then not get a drink?

I've attached a few items here: two versions of the AR-4 schematic; a revised version of the AR-4x schematic you referenced, and a pic of the crossover of my very early AR-4.

I have never wired up any replacement L-pads so am unable to comment on your re-build, but what I find interesting here are the coils. If I read your photos correctly, it appears that your AR-4 has the larger coil (presumably #5 w/225 turns), while your 4x has the smaller coil (#4 w/ 200 turns). The 5 coil in the AR-4 seems consistent with the original AR schematic (provided by Tom T.), while the coil remains undesignated in the color Korean schematic. I believe that during the long production run of the AR-4x, both the 4 and 5 coils found their way into the cabinets at various times, and could represent the time period when the production was shifting from the 4 to the 4x.

The thing that has me a bit perplexed now is that if you look at the crossover of my speakers, you clearly see that the AR-4 began production with a #4 coil (my speaker s/n's are under 200), whereas it seems the common knowledge suggests that the AR-4 more typically used a #5 coil.

BTW, your pot corrosion looked very typical. There is debate about whether new caps take time to "break-in" properly, so it would be good to hear your observations after a couple weeks of listening. Also, I'm curious to know how much high-end variability you get from your new tweets with the new controls, and where you have them set.

Nice job.

[commasense]

Thanks for the comments, guys.

Kent: Before I started, I was concerned about possible differences in the coils, but I had found somewhere (probably here at CSP, but I can't track it down now) a components lists of various AR models, and it said that the AR-4, AR-4x, and AR-4xa all used the same coil, as ra.ra states above. BTW, it's the 4x that has the coil marked "200," not the 4.

If the coils do have different values, what effect will that have? I presume it would alter the crossover point somehow, but in what way? IOW, does a higher value raise or lower the frequency, and by how much?

What would RoyC's goop do for the tweeters, and where can I get more info about it? Can I make some myself, or do I have to get it from him?

I didn't mention the difference in the woofers, but obviously the one in the 4x has a foam surround. It occurs to me that it may not be original, and that replacing it may have been the modification I saw evidence of when I opened it. I haven't done any careful A-B testing between the two, but there's no really obvious difference in bass response. Any comments on whether I should be concerned about a foam woofer?

Any thoughts on the difference between the standard 4x schematic and the alternate wiring in my 4x? What effect would it have had, or why it might have been done?

Thanks again for all your advice and help.

[JKent]

Hi Comma

I could be mistaken about the coils--I have no 1st hand experience with the AR-4. ra-ra is correct. AR did use the #4 coil in earlier 4x's and the #5 in later ones. I remember doing a 4x restoration once with mismatched coils and I made them both #5. Honestly I doubt you'll hear a difference but will leave that for more experienced people to comment on.

The different caps OTOH WILL make an audible difference. The 4x, with its 20uF cap crossed over much lower than most 2-way speakers. The 6uF cap in the 4 crossed over much higher than the 4x.

Roy developed his goo as a recreation of the original butyl rubber/toluene dope used by AR and KLH on cloth woofer surrounds. It's nasty stuff to concoct and best to buy from Roy or from Vintage AR (V_AR will cost much more). This is it: http://www.ebay.com/itm/ACOUSTIC-RESEARCH-CLOTH-SURROUND-WOOFERS-SEALANT-KIT-ALSO-KLH-/190759591395?pt=LH_DefaultDomain_0&hash=item2c6a285de3

As I said, if your tweeters are from V_AR they are already treated. Roy said Larry applies it to "tame" the PRT tweets and make them sound more like an original AR.

Now speaking of the goo. Are you sure your 4x has a foam surround? It looks like cloth in the photo and the earlier 4x's did have cloth. In fact, of the 6 AR-4x's I've worked on, all had cloth surrounds.

Your AR-4 may not have an original AR woofer, and from the photos it looks as though it may have been treated with some DIY goo but definitely NOT Roy's. Many woofers have been damaged by concoctions of Elmer's glue, latex caulk and who knows what else. Roy's stuff is very thin and never really fully dries. It remains totally flexible.

Maybe he will comment on your woofers and xo's.

Kent

[Steve F]

Crossover frequency as spec'd by AR was 2000 Hz for the 4 (and 'old' 2x, which used the same 3 1/2" tweeter).

Crossover frequency as spec'd by AR was 1200 Hz for the 4x (and also for the 'new' 2x, which used the same 2 1/2" tweeter).

Virtually all 4x's used the cloth surround woofer. Only at the very end of its production life did the 4x transition to the foam surround woofer that was used in the 4xa. it was probaly the same woofer as in the 6 and 7 at that time, 1974-75. The very first 6's in 1971 had a completely different woofer.

The cloth surround 4x woofer had a FAR of 30 Hz; the 6's foam surround woofer had a FAR of 25 Hz, so they were in fact, completely different woofers.

Steve F.

[commasense]

Take a look at the picture of the two speakers in the post above. The woofer in the 4 has a yellowish surround which I presume is treated cloth. The one in the 4x is grey, which looked and felt to me like foam. As I said, it may not be an original AR.

Unfortunately, I didn't think to take pictures of the two woofers while I had them out, or even visually compare the backs of them.

I don't have time now to check, but I posted the serial numbers of each in the OP, and they're visible in my restoration post, so we could cross check the 4x's date of manufacture.

Does anyone know why the yellow spot on the tweeter seems to have switched from the 4 to the 4x? Does that correspond with the change in the schematic? The red spot on the woofer didn't change between models. Could the 4 tweeter have had opposite polarity to the 4x's tweeter, that is, plus is the right terminal on one and the left on the other?

[JKent]

I have worked on 4x's with serial numbers higher than yours and lower, and all had cloth surrounds. Your 4x may have had a woofer swap, or a damaged cloth surround may have been replaced with foam, but to my eye it looks original and it looks like cloth. The 4 woofer OTOH does not look right to me. AR frames, AFAIK, were round. Yours is not. And that yellow stuff looks wrong. Below is a photo of woofers all pulled from AR-4x's. Some have bigger magnets, some have ribbed cones. They all have cloth surrounds. The one in the lower right corner looks like yours: 8 holes, smooth cone.

Most important: How do they sound? If they sound good, then...Good!

Regarding the yellow spots, I know some ARs were intentionally wired with the tweeter polarity reversed (the 4x, if memory serves and if I'm reading JFO's schematic correctly). In fact, I've seen woofers with the polarity reversed. OTOH, those are 2 different tweeters so the physical location of + and - would not necessarily be the same.
Kent

[RoyC]

Take a look at the picture of the two speakers in the post above. The woofer in the 4 has a yellowish surround which I presume is treated cloth. The one in the 4x is grey, which looked and felt to me like foam. As I said, it may not be an original AR.

Unfortunately, I didn't think to take pictures of the two woofers while I had them out, or even visually compare the backs of them.

I don't have time now to check, but I posted the serial numbers of each in the OP, and they're visible in my restoration post, so we could cross check the 4x's date of manufacture.

Does anyone know why the yellow spot on the tweeter seems to have switched from the 4 to the 4x? Does that correspond with the change in the schematic? The red spot on the woofer didn't change between models. Could the 4 tweeter have had opposite polarity to the 4x's tweeter, that is, plus is the right terminal on one and the left on the other?

commasense,

Your woofers are original to their respective models. The AR-4x surround is simply a much lighter cloth than the AR-4 woofer surround. The AR-4 woofer has a larger magnet than most (but not all) 4x woofers, and has slightly different response characterisitics. The 225 turn (#5/1.2mh) coil rolls off the woofer sooner than the 200 turn (#4/.88mh coil), but I wouldn't worry about it given you have 2 different woofers.

The application of my surround treatment to the cone of the Parts Express replacement tweeter is an attempt to calm down a peak in the response of this tweeter. It is marginally effective at best, and I wouldn't purchase the sealant for that purpose alone. The original 4x tweeter had a treated cone, so I'm sure Larry continues to apply it for visual reasons as much as any other. :-)

Carl's ("Carlspeak") crossover modification is a much more effective modification to the response of this tweeter.

The yellow dot usually represents the + side of the AR driver (except for some AR-2ax mids). The AR-4 tweeter was wired in like-polarity to the woofer. The 4x tweeter was reversed relative to the woofer. With the new tweeters, your specimens are not really 4's or 4x's, so standardizing your crossover was a good move. You could try reversing the polarity of your tweeters to see which is preferabe to you.

Roy