AR-4 series speakers

[ra.ra]

My modest collection of classic AR's includes three pairs from the 4 series: two pairs of 4x's and one pair of 4's, and even with all that I've learned by reading posts on this site and performing surgery on my speakers, I am still looking for more information and further opinions.

1. Capacitors.

My early S/N AR-4's have been restored (pot restoration, re-cap, re-dope, cabinet refinish), including original wax cap replaced with 6 mf Erse Pulse-X caps. These speakers sound terrific. See pic 1 for re-cap.

Pair 1 of AR-4x had similar level of restoration, with original wax cap replaced with 20 mf Dayton cap. See pic 2 of original crossover. These speakers sound very fine as well, but I currently like the 4's better.

Pair 2 of AR-4x (my beloved pair that I bought as a teenager 40 years ago) are still on the operating table, and I have two concerns with this pair. First, this pair does not have the wax cap by Industrial Condenser Corp. - - - instead, they have the Sprague Compulytic cans - see pic 3. So, my first question is: are these the caps that typically retain their value, or should I just go ahead and replace them?

2. Tweeters

My second concern is that one tweeter appears dead - - no response from battery test or multimeter. This is my very first experience with a 'dead' driver of any type, and I am curious to undertand what may have occurred to render it useless. Visually, it looks exactly as fit and robust as its still-living brother, and these speakers have always been handled, transported, and installed as a pair. What sort of things might happen that make a speaker driver give up the ghost?

3. Potential Mod

While I am probably inclined to replace the dead tweeter and restore to original, the thought did occur to me that there might be a possibility to convert this pair of 4x's into a pair of 4xa's, thereby leaving me with one pair each of 4's, 4x's and 4xa's. Of course, I would then have to obtain two 1-1/4" tweeters (instead of one 2-1/2" cone) and configure some type of adapter ring for them to fit the baffleboard openings, but what adaptations would be required to the crossover - - i.e. wiring, control and capacitor? I do not think I have ever seen a schematic for the 4xa, but I know it crosses over at 1600 Hz as opposed to 1200 Hz for the 4x. Also, could this be done with the original A-P pot or would a two or three-position switch be required for tweet control? Any thoughts on this - - - easy and interesting DIY project or simply a bad idea?

[Carlspeak]

Can't say for sure what might have happened, but if the voice coil is dead, the cause could have been overdriving or amp clipping.

I hope in the next few weeks to work up a 4x mod with phenolic ring tweeters and a new xover. Will share the results when complete.

[ligs]

I wonder if anyone has worked out a crossover scheme for AR4 series woofer and one of the widely used(and more modern) 1.25 inch highrange 1210038. 1210038 is almost like an universal tweeter and has been used in more models than 4x and 4ax tweeters and this includes the highly regarded 93, 94, 18 series. Intuitively one can crossover AR4 series woofer with 1210038 with just a highpass capacitor for the tweeter.

[ra.ra]

Thanks for the feedback, Carl and ligs.

Carl:

Regarding my dead tweeter, your guess is as good as mine regarding cause of death. I've always used these speakers with very modest wattage amplifiers and at moderate volume levels, so all I can say is that the speakers have never been run too hard, and definitely never abused. Meanwhile, I shall look forward to seeing results of your forthcoming 4x mod project.

ligs:

I think I follow most of what you are saying - - - I know there are several varieties of the 1-1/4" tweeter (p/n 200035, 200014, 200005, etc.) but I cannot keep straight all of the different tweeter part numbers and the speaker models they were initially specified for. Regarding my proposed mod, I am just trying to get some more information (x-o schematic), opinions (good idea or not?) and advice (how-to) about how I might adapt a pair of 4x's (in need of repair) essentially into a 4xa speaker.

The attached pic here suggests basically what I'd like to end up with - - I have original 4x cloth woofers and I am thinking of installing some later date rear-wired 1-1/4" tweeters with necessary revisions to the crossover. Can anyone direct me to a wiring schematic for an AR-4xa?

[ra.ra]

After doing a bit more digging regarding the 4xa, I was able to find the attached images - - I found the hardline schematic here on CSP, while the freehand schematic and x-o pic were cribbed from a post on Audiokarma site. It seems others have claimed never having seen a schematic for the 4xa, so this is offered for viewing and comment.

Still not sure yet which plan I will pursue - - - Option A: re-store this pair of 4x's (replace single dead 2-1/2" tweeter, replace 20 mf caps, clean pots, re-dope woofs, etc.); or attempt Option B: transform 4x speakers into 4xa's (replace with later model 1-1/4" cone tweets and switch caps with 10 mf values).

My understanding of crossover operation is rather limited, so here's where I would need more technical advice. If pursuing Option B, what to do with tweeter control? Can I keep the original A-P pot and just drop in 1-1/4" tweet and 10 mf cap and keep the wiring similar to 4x, or would additional resistor(s) be required? And if I cannot use A-P pot and need to replace with switch, should this be a two-position switch (like AR-7) or a three-position switch (like AR-6), and what are electronic specs for switch designation?

Lastly, regarding catalog page shown in final attached image, is it correct to assume that the tweeter noted for the 4xa (1-1/2", 38 mm wide dispersion cone) is indeed a typo, and that it should read similar to the tweeter for the AR-7, AR-6 and AR-8 noted in this same brochure (1-1/4", 32 mm)?

[ligs]

According to 1986 AR parts list, 1 1/4 inch tweeter(120005) is the replacement tweeter for both 4xa and 6, 7. After that there are no less than 3 other 1 1/4inch tweeters used in different models with 1210038 used in the majority of later AR models.

http://www.classicspeakerpages.net/library/acoustic_research/special_sections/additional_ar_documents/ar_parts_list_price_sheet_n/ar_parts_list_price_sheet_n_4.html#previous-photo

[ra.ra]

Thanks again for your comments and the link to the 1986 parts list - - - stupid me, I had overlooked how much specific chronology is actually contained in these parts lists.

The parts list for 1979 (see attached), most likely prior to the development of the 210038 tweeter, actually has two additional bits of information which I find interesting and useful. First, the weight of the magnet is noted (2.4 oz and 3.0 oz), and I assume this translates to 2-1/8" diameter and 2-3/8" diameter, which are the only measurements I am able to make. Secondly, I see that tweet 200014-3 calls itself a "pressure highrange", which I assume is another way of suggesting that this is among the first of the ferro fluid tweeters, since it i sshown to correlate with the smaller models in the ADD series (AR-17 and 18).

Now, any suggestions how to wire up the crossover: switch or pot?

[JKent]

Here's something out of left field: Take a look at Post #13 here: http://www.classicsp...6659#entry89404

Following Roy's mod, I replaced the AR4x drivers and xo with those from an Avid 100. It's a perfect drop-in replacement. The Avid even has a film capacitor. Drivers are a bit more modern than the AR. Woofer surrounds are rubber. Cabinet size is about the same but the AR is nice walnut veneer while the original Avid was crappy vinyl.

Kent

[ra.ra]

Thanks JKent, I read this post some months ago and found it very interesting, mostly because of the ease of transition - - take the guts out of an excellent (but ugly) speaker (vinyl Avid) and drop components into stylish walnut box (4x) of similar dimensions. It couldn't get much simpler, and the result looks (and sounds, I presume) terrific. I am totally unfamiliar with Avid products, but the drivers look very similar to some I have in other speakers - - - the 8" rubber surround woofer from an EPI-100; and the phenolic tweet from a Rectilinear XI (see attached).

What I am considering - - - not unlike your own conversion (modernization?) project of AR-3 to 3a - - - is a conversion of AR-4x to 4xa, and the main reasons this appeals to me are:

1. One 4x speaker already has a dead tweeter, so I need to do something to fix this.

2. I love all of AR's 4-series (size and proportions, personal history, simplicity), and after this tweet died, it occurred to me that maybe, after proposed mods, I could then own one pair each of the complete trifecta (AR-4's, 4x's and 4xa's).

3. I like to take these speakers apart, make some revisions, put them back together, and then convince myself that I have made some improvements.

Final decision and direction on this project (restore original 4x or "create" new 4xa) will probably be determined by which tweeter(s) I end up obtaining, but in the meantime, I am still hunting for advice from more experienced electronic wizards about how to adapt a 4x crossover to work with 4xa drivers.

[JKent]

I don't know who made the Avid drivers but your mention of EPI reminds me: I seem to recall some AR enthusiasts advocating the EPI inverted dome tweeter as a replacement for one of the ARs (3a maybe?).

The back of the Avid woofer reads:

DR 119

28878

2857610

"IF" 119 is the EIA code, the woofer was made by Automatic Manufacturing but I never heard of them.

I dunno.

Kent

[HarryM]

ra ra,on the price list from 1986 the replacement woofer for the 4,4x,4xa,6,7,15,16,17,18, and 25 are all the same.The 1"1/4 tweeter was used in the 4xa,6,7,17,18 and 25's.It seems like the changes in the cross overs for these speakers had to do with cabinet size so I would think if you used the cross over from the one wih the closesed cab size that woud give you a good starting point.

[ra.ra]

While I feel reasonably adept at some of the product research and the hands-on mechanical and wiring procedures, my knowledge tops out very quickly when it comes to the inter-workings of the various components (drivers, caps, resistors, inductors, controls) that shape the frequency output of any crossover network; and hence, I turn to more knowledgeable, creative, and experienced members for advice and suggestions.

ligs:

Looking back at your query in post #3, you've pretty much identified what I am trying to understand a little better in order to put together my own hybrid of sorts, but even before the arrival of the AR-18, there were at least three "classic" AR models that featured a very similar combination of drivers, each with a different cabinet size and its own crossover. Some early AR-6's had a pot control, one cap, and two coils. The x-o for the AR-7 had a switch control, one cap and no coil. The schematic for the 4xa (one switch, one cap, one coil) which I included in post #5 seems most similar to the 4x (one pot, one cap, one coil), and I suspect it is some version of this configuration that I am trying to achieve.

Harry M:

No doubt that cabinet volume is an integral factor in the make-up of a crossover (and, as I've stated, I do not pretend to understand the complex science of speaker design), but in the case of the three models within the 4 series, there are two factors we might think of as constants: the woofer and the cabinet volume. The primary difference among these models is the tweeter driver, with its associated capacitor and resultant x-o frequency, and I'm just fishing around for advice on how I might get optimal performance if I were to drop a 1-1/4" tweeter into an original 4x cabinet, keep the coil, and maybe even keep the pot control.

Thanks again, and I hope I have this little summary correct.....

AR-4: 3-1/2" tweeter, 6 mf cap, x-o at 2000 Hz

AR-4x: 2-1/2" tweet, 20 mf cap, x-o at 1200 Hz

AR-4xa: 1-1/4" tweeter, 10 mf cap, x-o at 1600 Hz

[ligs]

I just saw this on eBay: http://www.ebay.com/itm/Acoustic-Research-1-1-4-Cone-Tweeters-for-AR-4x-xa-6-7-8-18-25-28-93-94-s-b-bx-/230842861897?pt=Vintage_Electronics_R2&hash=item35bf4e8949

"AR 1 1/4" Cone Tweeters. These tweeters were removed from a pair of AR-18b speakers.

Static resistance measures 5 ohms. The tweeters have been tested with a frequency generator, and work fine. The model number on these tweeters is 200038-0. They also have the numbers 561 8138, probably a lot number. They are 3 1/2" in outer diameter, and the mounting holes are on 3" center-to-center diameters.

These are exact replacements for AR-6 AR-7 AR-8 AR-8s AR-8b AR-8bx AR-18s AR-18b AR-18bx AR-25 AR-28s AR-28b AR-28bx AR-93 AR-93s AR-94 AR-94s speakers. For AR-4x speakers, you would have to drill new holes to mount the tweeters (original AR-4x tweeters have a larger faceplate); for AR-4xa speakers, you would have to attach wires to the rear speaker terminals and bring them forward (AR-4xa original tweeters are designed for terminals on the front of the speakers). They are much better than the cone non-AR replacements available for the AR-4x and AR-4xa, which is why I mention them. "

What do you think? It would be nice if it is that simple.

[RoyC]

The model number on these tweeters is 200038-0. They also have the numbers 561 8138, probably a lot number.

"561" is the manufacturer's code #.

"8138" means they were manufactured in the 38th week of 1981.

Roy

[ligs]

Since I had some spare time I just thought to have a cursory look at AR 4x woofer and AR 18 tweeter combination in an AR 4x cabinet. AR 18 tweeter(1210038) was in series with a 8uF film capacitor and mounted on an adapter plate over the hole of the AR 4x tweeter(which was non-working). I used Stereophile’s test CD and a Radioshack’s analog sound meter fixed at 1 meter to the center of the test speakers. The apparent conclusion was AR 18 tweeter appeared to be at least 6 db more sensitive than the AR 4x woofer.

In the graph, tweeter 1 was connected in phase with the woofer, tweeter 2 was out of the phase of the woofer. I used Boston Acoustics HD-8 as a reference for its flat response. These were raw response curves without calibration. RS sound meter has been know to have a peak around 5 kc Hz but otherwise relatively smooth with attenuation at both high and low ends.

[ligs]

I added an 8-ohm L-Pad to the AR 18 tweeter circuit. Now the AR 4x woofer is in balance with AR 18 tweeter with reasonable flatness!

[ra.ra]

Regarding the eBay reference for the pair of tweets for 89 clams, I'd never be tempted to pay that price but yes, this is the basic tweeter type I am talking about. (Again, I am not fully familiar with all of the specific differences between p/n 200038, 200014, 200005, etc.)

It sounds like your situation (dead 4x tweet) and curiosity (how to replace with a later model 1-1/4" tweeter) is similar to mine, so I am following your experiments in the speaker lab with great interest. I certainly notice the flatter response in your most recent test, but I remain curious how you arrived at the decision to try a cap with an 8 mf value. Apart from trial and error, this is where I would be completely lost.

I assume this is all temporary experiment at this point, in which case a permanent solution may not have arrived yet, but what did you use for your adapter plate - - - heavy sheet metal?.......thin tempered masonite? Also, am still wondering whether an original 16 ohm pot could work its way into a similar crossover solution?

Lastly, graphs and charts and test equipment aside, subjectively speaking, how does this assembly sound with your favorite music?

[ligs]

I am using a circular piece of ¼ “ spray-painted Masonite for the adapter plate. I figure if it is good for mounting the Advent Loudspeaker woofer it is good enough for me; I then temporily mounted it over the original AR 4x tweeter hole using only two screws. Since I was only interested in the crossover region I did not even completely sealed the enclosure.

The original AR 18 has a crossover of 2000 Hz and the tweeter is high-passed only with a 5-6 uF capacitor. So I figure using 8uF will help it extend down to 1500 Hz( 2000 / 8/ 6) to better blend with the 4X woofer.

The use of an 8-ohm L-Pad was just because I had it in my tool box. Of course some of the experts can run a computer assisted simulation for a more definitive design but I don’t have accurate measuring equipment nor design experience. May be Carl can help with this?

In terms of sound quality, all I can say is it sounds much better with a L-pad than with the tweeter running flat out.

[ligs]

Attached is the crossover schematic for this AR 4x woofer/AR 18 Tweeter package:

The attenuation of the tweeter via the L-pad is about 6 db (0.25x in power input vs the woofer).

The following link has some info on similar subject. It mentioned that Roy Allison designed the tweeters used in AR 6, 7, MST, which led to AR 4Xa and apparently(my guess) many later 1.25-inch tweeters, including the AR 18 series.

http://www.audiokarm...p/t-243950.html

I also like the 1-inch inverted dome tweeter used in EPI and Genesis speakers. It is very simple to use, in many cases, just a 5-6 uF high-pass capacitor with a proper woofer.

[HarryM]

Iigs,why didn't you try the 10mf cap like in the 4xa.It crosses over at 1600Hz.If this is a stupid question I'm OK with that because I really don't understand cross overs yet.LOL.

My logic is this,if the 4x and the 4xa use the same woofer and cab but the 4xa uses a very similar tweeter to the 18 shouldn't it be the same cross over as the 4xa?

[ligs]

Harry,

You are absolutely right. 10uF probably could probably work even better and may fill in the slight dip around the crossover region(some people may call this a BBC dip saying this is the secret to the magic sound of LS3/5A monitor )! When I perform the final fix on the crossover I will voice it by varying the capacitor from 8 uF to 20 uF.

[HarryM]

I'm looking forward to your findings.

[ra.ra]

Likewise, I'm very curious to hear your opinions of any further changes to your makeshift crossover. Are you thinking of trying different cap values?

The masonite adapter ring seems to work fine, but if it becomes a permanent installation, you may want to try masonite (generically called "hardboard") which should be available in a thinner 1/8" thickness - - - tempered hardboard is far superior to non-tempered - - - stiffer, smoother surface and cleaner cut edges. Also, gotta say I love the little schematic you included in post #19.

[ligs]

Thanks for the your interest! The adapter ring is made of very stiff Masonite. It appears to be the same material used in early version of EPI inverted tweeters and the ring around the first generation the woofer of "The Advent Loudspeaker"

I still have many AR driver parts laying around. I am glad this thread got me into doing something with them. I have been a fan of AR speakers and I had AR3, 11, 9, 2aX and 4X in the past. However, I have moved into metal cones and metal domes especially those so-called CMMD (from Infinity) and Magalloy(from High Res AR). With certain music, those ultra-stiff drivers seem to provide a little more realism than the paper drivers.

At this point, I have 2 AR 4X cabinets, 2 pairs 8-inch woofers from AR-4X and AR18, 2 pairs 1.25-inch tweeters from AR-18, a couple pairs of AR1MS, a pair AR-3 cabinets ( midrange not working), and 2 NHT 1259 woofers(used in NHT 3.3). While nothing is quite equal to the bass section of AR9, the NHT 1259 12-inch woofer with 13 mm linear displacement(26 mm p-p) comes pretty close!

[ra.ra]

Hey ligs, just wondering if you've conducted any further experiments on your hybrid speaker?

I started thinking about this again when I stumbled onto the AR-4xa speakers shown in the pics attached, which are being auctioned on eBay UK. Can't say I've ever seen this particular configuration before, but it basically shows the combination of components that I discussed trying to combine in my 4x cabinets.

Aside from the point of sale (Great Britain), the only indication here that suggests to me that these are Euro products is the listing of a second factory address on the bottom of the s/n card. And, although I haven't included an image here and am no expert on wood species, the grain structure of the cabinet veneer shown in the original post almost appears that it might be English, rather than American, walnut.

Another hybrid of sorts? Pic 1 shows grille cloths with square badges more typical of 4x's rather than the rectangular 4xa badges. Pic 2 shows the expected 1-1/4" tweets (with two types of wire leads) and woofs with cloth surrounds in lieu of foam. Pic 3 is the one that surprised me, though - - - first time I've seen AR-4xa speakers with variable rheostat tweeter control.

So now I'm wondering what's inside these babies . . . and if they might be wired just like the US AR-4x, but maybe with a 10 mf cap (4xa, x-o at 1600 Hz) instead of the 20 mf cap (4x, x-o at 1200 Hz). Hmmmmm........

Thoughts, anyone?