I've got the bug! and a SN question

[JKent]

Well, I've got the AR restoration bug thanks to you guys! I restored my 4x's (originally purchased in 1969)and am almost finished with a pair of 2ax's. Much help along the way from great forum members!! Thanks!Will post pics when finished.

So now I've bought another pair of 4x's on eBay, and will be restoring them some time in the future. I say "pair" but the serial numbers are vastly different. One speaker has a particle board back and is serial # 377193 (no letters). The other has a plywood back and is serial # FX66427. My other pair--the ones I bought in '69--have particle board backs and are SN FX 262692 and FX262765.

Can anyone tell me anything about these? Are there clues in the SNs? Thanks!

[johnieo]

>One speaker has a

>particle board back and is serial # 377193 (no letters). The

>other has a plywood back and is serial # FX66427.

>My other

>pair--the ones I bought in '69--have particle board backs and

>are SN FX 262692 and FX262765.

Hello Kent:

Somewhere between serial number 175,000 and 225,000, AR changed the characteristics of the AR-4x slightly. Data collected from a number of folk show:

* for SN less than 175,000 (June 1968)

AR-#4 coil (0.88 mH), 20 uF capacitor

18 oz of fiberglass stuffing

crossover frequency = 1,400 Hz

* for SN greater than 225,000 (Jan 1969)

AR-#5 coil (1.2 mH), 20 uF capacitor

12 oz of fiberglass stuffing

crossover frequency = 1,200 Hz

It appears that 3 of your 4 units are of the later variation, so you might consider altering the coil and removing 6 oz of stuffing in the early unit.

If you look at Tom Tyson's inductor chart posted some time ago, you will see that the #4 coil has 200 turns of #17 enameled wire, whereas the #5 coil has 225 turns of same. If you have ~ 11-12 feet of that wire from another coil, you may carefully scrape away the insulating varnish from the ends, solder, cover joint with shrink tubing, and tightly wind 25 additional turns. Won't look as pretty as an original, but it will have the correct inductance.

[JKent]

Thanks John. I found the chart and read some of that thread. Sounds like there are no suitable aftermarket replacement inductors, and I don't happen to have any 17 ga (17????) wire lying about. This will be a future project, and I may just leave the #4 and see how it sounds. In the meantime an inductor may show up on eBay, although I cringe when I see classic speakers "parted out"

Thanks for ALL your help. My 2ax project is almost complete, and I'll post pics.

[charger3834]

Why don't you just leave the old speaker alone for the time being and let us know how it sounds to your ears. There is always room for a little subjective evaluation here. I own a set of 1969 229xxx myself, and I would be interested if there seemed to be any meaningfull difference.

I am also interested to see your AR-2ax restoration pictures.

[JKent]

Thanks Brad. Yes--I think I will listen first. The two won't be matched, but in real listening rooms, it may be impossible to tell the difference.

Waiting for some paint to dry thoroughly before installing the new grille cloth, and there is a little more touchup sanding before applying the oil finish, but the 2ax pair should be complete this week.

While we're on the subject, are there any guidelines for posting pics here? I don't want to clog up the forum's server with jpegs that are too big.

[charger3834]

Check with Mark(administrator)on the pictures.

If I were a betting man, I would bet that the two variations of the AR-4x would not be significantly different from each other. A lot of these subtle differences "blend" in the far field. This is how the great minds at AR intended us to listen anyway.

[RoyC]

>One speaker has a

>particle board back and is serial # 377193 (no letters). The

>other has a plywood back and is serial # FX66427.

It appears AR stopped using the "FX" in the serial number sometime after #FX351713 and #358017 according to the 4x's I have here. The "FX" was apparently used to designate the AR-4x and "F" was used for the earlier AR-4. By the time those high numbers were manufactured, the AR-4 was in the distant past...

The AR-4x woofer varied in appearance, and from some limited testing I have done, varied somewhat in response and sensitivity. This may have been the reason for the inductor and damping material change.

Attached is a photo of three 4x woofers. From left to right, earliest to latest. I used to have a pair with the same later style ribbed cone on the right, but sporting a (deteriorated) foam damping ring around the dust cap (serial # was around FX199000). All of the ribbed cones I have seen, including the damping ring version, were served by a #5 inductor. The "smooth" cones I have seen to date have the earlier crossover utilizing the #4 woofer inductor.

AR manufactured so many of these little buggers, that it may take us awhile to figure out all the nuances of the design evolution:-).

Tom T. may have better insight into this one.

Roy

http://www.classicspeakerpages.net/dc/user_files/1358.jpg

[charger3834]

>

>The AR-4x woofer varied in appearance, and from some limited

>testing I have done, varied somewhat in response and

>sensitivity. This may have been the reason for the inductor

>and damping material change.

>

This is exactly what I was thinking. Often AR made changes to crossovers to accomodate new drivers. As I have said before, we need to think about what parts go with what. We can't just make changes without controlling the other variables in the equation.

[RoyC]

I need to correct a couple of mistakes. It was too late to edit my post.

>It appears AR stopped using the "FX" in the serial

>number sometime after #FX351713 and #358017 according to the

>4x's I have here.

The above should read "BEFORE #358017"

>I used to have a pair with the same later

>style ribbed cone on the right, but sporting a (deteriorated)

>foam damping ring around the dust cap (serial # was around

>FX199000).

The ribbed cone with the damping ring was around FX299000 not FX199000.

Hi Brad,

John O'Hanlon has collected much data on the AR-4x (as well as built some beautiful 4x cabinet reproductions):-). In our comparisons it seems, regardless of the original reason for the inductor/stuffing changes, all iterations of woofers and tweeters of this two-way system consistently sound "right" with the #5 inductor and the lesser amount of stuffing. The actual differences between the drivers are quite subtle.

Roy

[charger3834]

Roy,

You, John and others do outstanding research, but I guess I have trouble with the idea that the #4 inductor with additional stuffing was somehow not right.

[johnieo]

>Roy,

>

>You, John and others do outstanding research, but I guess I

>have trouble with the idea that the #4 inductor with

>additional stuffing was somehow not right.

Hello Brad:

Thanks very much for your input--it is interesting to attempt reconstructing this speaker's history. Two comments: First, recall that AR changed the stuffing and coil in the AR-3a at about the same time. The AR-3a switched from #7 (1.9 mH) coil with 28+ oz stuffing to #9 (2.85 mH) coil with 20 oz stuffing. This was done, according to Roy Allison via Tom Tyson, to correct a bump in the upper woofer range. This change slightly reduced the crossover frequency from 575 to 525 Hz. If the AR-4x crossover were changed near the end of 1968 for a similar reason, it would not have set a precedent, but we don't know that.

Second, the data collected on a number of speakers show a random ordering of drivers but not coils. e.g., the cabinets whose serial numbers were less than 175,000 showed a mix of smooth cone and ribbed cone woofers. Ditto for those over 235,000-- a mix of smooth, ribbed and ribbed with damping rings. We don't know any more than what we see.

Were we able to combine AR factory historical data with our observations, we might develop a more complete picture!

[charger3834]

These really are interesting animals. For me the investigation and documentation is the fun part. I really think some of the work you guys are doing is great. I really like the academic approach. These things were designed by an academic approach, so why shouldn't they be collected/restored the same way. I think this site is becoming a profound reference for anyone interested in AR. It seems as if interest grows each week.

[RoyC]

Hi Brad,

After our 2ax tweeter adventure, I know you enjoy the detective work as much as we do:-)!

John reminded me of another variation of the 4x woofer. It is very similar to the woofer in the center of my photo (which is actually a "lightly" ribbed cone) but has a completely smooth cone, with no damping ring. I believe Tom T. mentioned that the 4x woofers were made by more than one manufacturer, so that could account for some of the differences.

It does appear that some of these woofer iterations were used with both inductors.

I have also found variations among 4x tweeters. Some are completely coated with sticky damping compound, some not very much, and others not at all. Sensitivity and response varies somewhat accordingly.

I am begining to think that the sonic difference between the inductors, which are quite close in value (.88mh vs 1.187mh) is probably less than that of the range of drivers used over the years.

With so many 4x parts floating around on Ebay, it is at least reassuring to know that the configuration with the #5 inductor will accomodate all the 4x drivers we have tried. On the other hand, getting a pair with widely differing serial numbers and different woofers to be a "perfect" sonic match may prove difficult, even if the inductors are the same.

Roy