AR 2ax chronology help needed

[Guest postjob62]

Hello all,

Having gotten my 4x's at least up and running, I now turn my attention to my 2ax's. I would like to procure another pair and as many replacement parts, drivers, etc. as possible to "bank" for future needs.

I have searched the archives here as wellas the "library" for chronological milestone info, but am not able to find very much. I know it's asking a lot, but if anyone has the time and inclination to post a 2ax chronology it would be very helpful to myself and possibly others. I know that the "new" version appeared circa 1970 and seems to be preferable from a listening standpoint, but beyond that I know very little.

My original pair have serial #'in the 170,000 range. Is that old or new? Is there any way to reasonably date 2ax's from the serial #?

Also, does anyone know when MDF back panels became standard? Mine have plywood, but I am looking at a pair that appear to be MDF or a like composite.

Thanks very much,

Ed

[Steve F]

This has been posted many times in the past on previous threads, but it's no problem whatsoever to do so again:

The original 2ax was introduced in 1964 as a replacement to the 2a. It retained the cloth-surround 10" woofer and 1 3/8" "fried egg" tweeter of the 2a, but replaced the twin 5" angled midranges with a new 3 1/2" cone. Crossover frequencies were 2000Hz and 7500Hz. The logo was a square brass "AR Inc." in one corner and a brass "a" in the other corner.

In 1968/69, the AR-5 was introduced, using a new foam-surround 10" woofer and an 8-ohm version of the 3a's 3/4" tweeter.

In 1970, the "new" 2ax was introduced, serial numbers above around 125,000. The new 2ax used the 5's foam-surround woofer, the 5's 3/4" tweeter, and the old 2ax's 3 1/2" midrange. Crossover frequencies were lowered to 1400Hz and 5000Hz. The logo was now the 3a/5 style brass with red de-bossed lettering, saying "AR-2ax".

The new 2ax was a superbly well-balanced speaker, and at one-half the price of a 3a, an outstanding value. The head of Advent's product development at the time used to complain to me that the 2ax was a "sneaky" speaker.

My 2ax's were s/n around 140,000 and they still had the plywood rear panels.

Steve F.

[Guest postjob62]

Stve,

This helps and thanks so much.

My current 2ax's are around #170,000 and they also have plywood backs. The pair I am looking at are around 201,000 and they have composite backs.

Thanks for the badge info, I forgot to ask that. I have misplaced mine, but found a set of the "AR, inc." badges that will work.

Ed

[charger3834]

This "which AR-2ax do I have" issue seems to be an ongoing topic here. Since the AR-2ax is one of the most popular models. We really need to have a section of the library to refer folks to. Perhaps a short history and a comparative spreadsheet. A couple of photos would work too. We could have a collaborative effort.

[johnieo]

>Crossover frequencies were 2000 Hz and 7500 Hz.

>

>In 1970, the "new" 2ax was introduced,

>Crossover frequencies were lowered to 1400 Hz and 5000 Hz.

Perhaps this explains why the woofer coils in my older AR-4x speakers were marked with a handwritten "2ax" (0.88 mH), but other AR-2ax woofer coils were marked "7" (1.9 mH).

[Steve F]

>>Crossover frequencies were 2000 Hz and 7500 Hz.

>>

>>In 1970, the "new" 2ax was introduced,

>>Crossover frequencies were lowered to 1400 Hz and 5000 Hz.

>

>Perhaps this explains why the woofer coils in my older AR-4x

>speakers were marked with a handwritten "2ax" (0.88 mH), but

>other AR-2ax woofer coils were marked "7" (1.9 mH).

I'm not sure what you mean by "older" AR-4x's...older than the new 2ax, or older than later 4x's? There was only one version of the 4x: It used a 2 1/2" tweeter crossing over at 1200Hz from the woofer.

The AR-4 (not 4x) used the 3 1/2" cone (the midrange in all the 2ax's), crossing over at 2000Hz from the woofer.

In any event, the difference between 1200 and 1400Hz is not significant, and given the inexact nature of determining "crossover frequencies" based on acoustic driver output vs. x-over voltage curves and typical x-over component tolerances of +/- 10%, the 4x (1200Hz) and new 2ax (1400Hz) might well have used the same woofer choke.

I also find it interesting that the new 2ax retained the 3 1/2" driver when the 4x and new 2x both replaced the 3 1/2" driver of the previous models (4 and "old 2x," respectively) with the 2 1/2" driver.

Why didn't the new 2ax use the 2 1/2" driver as the midrange and cross over at 1200Hz? I asked Roy Allison that question and he didn't give me an exact answer. I have a feeling that the marketing powers-that-be at the time didn't feel comfortable in replaceing ALL of the old 2ax's drivers AND its crossover and still retaining the 2ax designation.

I'm sure they wanted to keep the 2ax model number because it had built up some valuable marketplace equity in the 6 years from 1964-1970, but wanted to retain at least some thin line of continuity to the previous version.

Now, 35 years later, we'll probably never know.

Steve F.

[Andy]

Also....the early 2ax cabinets (below # 75,000) had solid wood front trim, the later versions went to veneer covered particle board. I just found a very early teak pair, #000234 & # 000222 which makes them among the earliest 2ax's around.

[johnieo]

>I'm not sure what you mean by "older" AR-4x's...older than the

>new 2ax, or older than later 4x's? There was only one version

>of the 4x: It used a 2 1/2" tweeter crossing over at 1200Hz

Steve: Pardon me for not being clear about using the terms old versus new. I was referring to the electrical crossover and damping changes in the AR-4x. I realize there was no driver change. The "older" AR-4x use a #4(0.88 mH) woofer coil and 18 oz Fiberglas, whereas the "later" AR-4x used a #5(1.2 mH) woofer coil and 12 oz Fiberglass. These changes appear to have been made around serial number 250-290,000.

This is the same issue we dealt with in the AR-3a. Its woofer coil changed from a #7(1.9 mH) to a #9(2.88 mH) in late 1969; its Fiberglass weight was reduced from 28 oz to 20 oz at the same time. (These changes were made around serial number 38-40,000.)

These real, physically distinct, observed, measured changes in inductance and in Fiberglass weight revealed a change AR-4x and AR-3a manufacture. The change would cause the system Q of these two speakers to increase, slightly increasing its bass response near and below cabinet resonance. This would have slightly reduced the crossover f in the AR-3a, but if so, that was likely a side effect. Thus, differences in acoustic vs electrical crossover may be correct, but moot. It would appear that an increase in Q was the prime reason for change.

However, back to the AR-2ax: Here I was wondering if there was a different reason for the coil change. You stated the AR-2ax crossover frequencies were reduced from 2000 Hz and 7500 Hz, to 1400 Hz and 5000 Hz. In this case it is clear that the woofer coil would need to be increased and by a significant amount to reduce the lower crossover from 2000 to 1400 Hz. Perhaps, my query asked, this explains the "2ax" marking on my 0.88 mH coils, and the "AR #7" marking (1.9 mH) on newer AR-2ax speakers. Doubling the inductance would reduce lower x-o by a factor of 0.7 x 2000 = 1400 Hz.

Has anyone observed stuffing weight changes vs serial number in AR-2ax?

[RoyC]

Of the 5 AR-4x's I have been into, 2 have the smaller #4 (.88mh) coil and 3 have #5(1.20mh) coil. Stuffing and serial numbers correspond with John's description above...part of an apparent AR trend toward larger woofer inductors and less stuffing.

I have a pair of the "newer" style 2ax's (serial #'s 234,xxx..late 1973) with the #7 (1.9mh) coil and 1.8+ lbs of fiberglass. That seems to put them in the "higher amount of stuffing" category.

Interestingly my older, 1971 pair of AR-5's with a similar woofer and essentially the same internal cabinet volume as the 2ax have only 1.3+ lbs of fiberglass.

Maybe that is due to the slight difference between the "longer throw" AR-5 and AR-2ax woofer that Tom T. has mentioned in the past. (The woofer part #'s in our Library's 1977 and 1979 replacement parts lists are different as well.)

I have another pair of 2ax's enroute and will report whats in 'em as soon as possible.

Roy C.

[charger3834]

I just found a very early teak pair, #000234 &

># 000222 which makes them among the earliest 2ax's around.

Very cool, especially to have them in oiled teak. I guess those would be 1964's.

[Guest robobxman]

A related question. I have an earlier pair of 2ax's (pre 1970). They are original. Interestingly, the woofers are on the top, unlike my post 1970 ax's (and most every speaker I know of). Does anyone know why these would have been designed this way?

[Steve F]

> Interestingly, the woofers are on the top, unlike my post 1970 ax's (and most every speaker I

>know of). Does anyone know why these would have been designed

>this way?

The only way the "top" or "bottom" would be determined is by the lcation of the logos. I assume you mean that the logos are on the tweeter/midrange end of the enclosure, instead of the woofer end.

Something worth considering: In the late-50's to mid-60's, so-called "bookshelf" speakers were intended, more often than not, to be used on their sides, horizontally, rather than vertically. A sideways-lying 2ax would fit on a bookcase very easily, its the 13 1/2" cabinet height dimension would fit neatly between the typical shelf spacing of a bookshelf.

Many early KLH speakers from this era had only THREE finished panels, with one of the long panels being unfinished, the thought being that the speaker would rest on that side in a horizontal orientation.

From a practical standpoint, if you use the speaker vertically and the midrange/tweeter is somewhat near seated ear level, there won't be a tremendous difference in the far-field response whether the woofer is up or down.

Steve F.

[tysontom]

>> Interestingly, the woofers are on the top, unlike my post

>1970 ax's (and most every speaker I

>>know of). Does anyone know why these would have been

>designed

>>this way?

>

>The only way the "top" or "bottom" would be determined is by

>the lcation of the logos. I assume you mean that the logos are

>on the tweeter/midrange end of the enclosure, instead of the

>woofer end.

>

>Something worth considering: In the late-50's to mid-60's,

>so-called "bookshelf" speakers were intended, more often than

>not, to be used on their sides, horizontally, rather than

>vertically. A sideways-lying 2ax would fit on a bookcase very

>easily, its the 13 1/2" cabinet height dimension would fit

>neatly between the typical shelf spacing of a bookshelf.

>

>Many early KLH speakers from this era had only THREE finished

>panels, with one of the long panels being unfinished, the

>thought being that the speaker would rest on that side in a

>horizontal orientation.

>

>From a practical standpoint, if you use the speaker vertically

>and the midrange/tweeter is somewhat near seated ear level,

>there won't be a tremendous difference in the far-field

>response whether the woofer is up or down.

>

>Steve F.

>

Steve is right: the orientation might seem to be upside-down, but in reality someone reversed the grill panel or placed the logo badge on the opposite end.

The problem with the "woofer-up" vertical placement has more to do with tweeter interference and diffraction effects from a table top or other adjacent surface if the speaker is placed on anything other than a free-standing speaker stand, which also is not the best method of mounting that speaker. With the tweeter "up," however, there is less interference from other surfaces adjacent to the speaker (except for edge-molding diffraction). All of these effects are pretty much lost in the far field anyway.

I wasn't aware that early KLH speakers were finished on three sides, but all early AR-2 versions in *any* finish were definitely unfinished on the bottom horizontal side to insure that the speaker was placed horizontally on a table or in a bookshelf. The reason was that (with horizontal placement) the dispersion of the two inward-facing 5-inch tweeters was broad in the horizontal plane, but quite narrow in the vertical plane (a design goal that engineers strive for today, incidentally). Placing AR-2s vertically upsets the acoustic-power response pretty significantly, so to encourage proper placement, it was determined that the one side need not be finished. This also reduced the manufacturing cost of this speaker, not bad since AR lost money on the first few-hundred units built. Henry Kloss might have taken this bit of knowledge with him to KLH, even though he was not at AR when the AR-2 was finally introduced to the public.

--Tom Tyson

[Guest postjob62]

Tom,

Does this horizontal placement apply to the 2ax as well? I've never known this! Please describe for me if you will the best way to place 2ax's, including height from floor, walls, corners, etc.

I just always assumed they were meant to be vertical.

Thanks,

Ed

[charger3834]

Ed,

Don't worry, the issue that Tom brings up really only applies to the AR-2. This is because that speaker needed the Dual 5" midranges sitting Horizontal to get maximum dispersion. If a person had AR-2a's instead, this would not be as big of an issue since the frequencies above 7500 HZ would be handled by the supertweeter. Note: all four sides of an AR-2a are finished.

Your second genneration AR-2ax's have tons of dispersion; just place them according to the guidlines we discussed previously.

[Steve F]

It's interesting about the optimal AR-2ax placement/orientation. The midrange and tweeter are side-by-side when the speaker is vertically-oriented. That is definitely not the best way to arrange the mid/high drivers if interference-free response is the goal.

This phenomenon was not really well understood by AR (or anyone else) at the time. Not until the intro of the AR-9 and the other Verticals (91, 92, 90) did AR really address this issue.

Therefore, the best mounting position for the 2ax (and the 10Pi, 11, and 12) may well be horizontal, since this orientation puts the midrange and tweeter in vertical alignment with each other.

The 3a and 5, by total happenstance (since vertical vs. horizontal driver orientation wasn't an issue at the time in the late '60's), are equally good (or bad, depending on your viewpoint) placed vertically or horizontally, since their midrange/tweeters are offset diagonally to each other, and are in about the same orientation whether the cabinets are tall or wide.

This entire matter is more important in the near field than it is in the reverberant field, so much depends on your listening habits, and, quite honestly, your sense (or your wife's!) of aesthetics.

Steve F.

[tysontom]

>Tom,

>

>Does this horizontal placement apply to the 2ax as well? I've

>never known this! Please describe for me if you will the best

>way to place 2ax's, including height from floor, walls,

>corners, etc.

>

>I just always assumed they were meant to be vertical.

>

>Thanks,

>

>Ed

Ed, the AR-2ax has the 3-1/2-inch midrange driver rather than the two 5-inch, inward-facing drivers of the AR-2a, so the 2ax speaker can be placed either horizontally or vertically. There is probably no discernable difference in horizontal or vertical placement, at least in the reverberant field.

All of the early AR bookshelf speakers were designed to be placed back against a wall, up off the floor, and out of the corners. Well, one speaker can be fairly close to a corner, if necessary, without ill effects. If you have a good bookshelf arrangement, however, and you can mount the AR-2axs with the front face flush with the shelf with books on either side, etc., the speakers will definitely sound much better by eliminating boundary-interference affects (the so-called "Allison Effect") that occur when you mount bookshelf speakers on stands, especially close to a wall. Boundary interference occurs at certain bass frequencies when an out-of-phase, low-frequency wave travels behind the speaker, bounces off the wall and "cancels" the in-phase output from the woofer at that frequency, thus causing a "suckout" attenuation of sorts for the bass response at certain frequencies. You can, of course, mount a speaker on speaker stands well out in the floor away from the walls, but the boundary effect is still there to a smaller degree from the floor, and then the bass output will be *seriously* compromised (attenuated with respect to other frequencies) in this position. Therefore, unless you can cut holes in the wall and flush-mount the speakers that way, which few people are willing to do, bookshelf-mounting is the next-best thing. Bookshelf-mounted speakers will also be facing a solid angle of 180 degrees, which is ideal, and which will help optimize the low-bass output as well.

Some additional thoughts: in a long, narrow room it is usually better to mount the speakers along a long wall to avoid unwanted room resonances; on the other hand, if the room has approximate 1:1.25 length and width proportions (10' x 12' or 13' x 16'), for example, then the narrow wall will do fine. As said before, you can allow at least one of the speakers to be close to a corner, but don't put both in corners or you can have heavy bass response. Usually, mount the speakers approximately 2-3 feet above the floor, perhaps one-third up from the floor to ceiling. Avoid placing the speakers equidistant floor-to-ceiling, if possible, or equidistant to the side walls. Space between each speaker should be determined by the approximate listening or seating position, but the speakers should be six to eight feet apart in any event for good stereo effect.

Let us know how you finally mount them!

--Tom Tyson

[tysontom]

>It's interesting about the optimal AR-2ax

>placement/orientation. The midrange and tweeter are

>side-by-side when the speaker is vertically-oriented. That is

>definitely not the best way to arrange the mid/high drivers if

>interference-free response is the goal.

>

>This phenomenon was not really well understood by AR (or

>anyone else) at the time. Not until the intro of the AR-9 and

>the other Verticals (91, 92, 90) did AR really address this

>issue.

>

>Therefore, the best mounting position for the 2ax (and the

>10Pi, 11, and 12) may well be horizontal, since this

>orientation puts the midrange and tweeter in vertical

>alignment with each other.

>

>The 3a and 5, by total happenstance (since vertical vs.

>horizontal driver orientation wasn't an issue at the time in

>the late '60's), are equally good (or bad, depending on your

>viewpoint) placed vertically or horizontally, since their

>midrange/tweeters are offset diagonally to each other, and are

>in about the same orientation whether the cabinets are tall or

>wide.

>

>This entire matter is more important in the near field than it

>is in the reverberant field, so much depends on your listening

>habits, and, quite honestly, your sense (or your wife's!) of

>aesthetics.

>

>Steve F.

I think what Steve F is referring to is the unknown-at-the-time D'Apollito effect first characterized by "Swan" speakers with their vertical midrange and tweeter arrangement -- preferably with a midrange on top, tweeter in the middle and another mid on the bottom. There is certainly less interference effects when the AR-2ax, AR-10/11 are mounted horizontally, as their midrange and tweeter are vertically oriented in this position. Whether there would be a discernable difference well back in the far field is questionable, but in many cases it is just as easy to mount these speakers horizontally as vertically.

--Tom Tyson

[charger3834]

Steve's driver cancelation phenomenon is probably a bit of an issue with all the 3 way systems to some degree. As Steve said, it was not a known issue in the 60's and AR was focased on the far field anyway.

Thanks for the refresher on the Allison Effect Tom !

My sense of it is that horizontal placement seemed to be more common in the 50's and 60's. I could be wrong since I did not exist until the 70's unfortunatly. I think the Horizontal placement is just a little cooler if you will.

Ed, you can check out Edgar Villchur's artical in the library entitled "How to get the most from your loudspeakers." It was published in HiFi/Stereo Review in October 1961. It has a good discussion on placement.

[Guest postjob62]

Tom,

Thanks much for the clarification on placing 2's as opposed to 2ax's. Brad and Steve, thanks for your input as well.

This raises another question: would the admonition against using stands with bookshelf speakers also apply to my 4x's? I've just gotten them and they sound great to me sitting on 6" of phone books on a carpeted floor, but I am in the process of building some appx. 28" tall stands to get the tweeters up to ear level. My plan was to set them very close to the back wall about 7' apart, based on something I thought I read in this forum about "close-to-wall" placement increasing bass. By WAF being final determinant even in my office, they can't go in corners due to existing furniture, so no problem there. I would hate to lose any bass response since that is part of what I find so appealing about the 4x's.

Brad, thanks, I have read Edgar's article and was just thinking to myself a couple of days ago about how it must still be pertinent today especially given that we are still using the same speakers. I also thought (ironically) that there was no mention of using custom-turned titanium isolation blocks or devices of sililar ilk to get the best sound. (Or was that unobtanium?) I have obsessed for weeks on the whole couple vs. isolate issue based on directives found in another forum, only to find that these little 4x's sound pretty good as described above, apparently violating every opinion proffered on this other unnamed forum.

Sorry to ramble- I guess this could be another complete thread! But believe me, the help is greatly appreciated.

As a postscript to the placement issue, I noticed a phenomenon a couple of days ago while listening to the 4x's. I'm in a small room, about 13x13x8, and I'm currently sitting about 8.5' from the face of the speakers. I inadvertantly noticed that the amount of bass I perceived changed dramatically as my head moved forward and back in relation to the speakers, with the increase coming as I got slightly farther away. I didn't imagine this, did I? I will admit to having tin ears at best.

Regards,

Ed

[Steve F]

A good rule of thumb when putting speakers on stands is to make certain that the three distances with respect to the woofer (up from the floor, to the wall behind them, and from the side wall) are all different and mathematically unrelated (no whole number multiples). This will spead out the reinforcement/cancellation modes over as wide a range of frequencies as possible, resulting in the smoothest in-room bass response.

If your room is square as you indicate (13 x 13), there is likely a bass reinforcement/cancellation mode at that location related to the fact that two of your room's dimensions correspond to the same bass frequency. 13 feet is the wavelength of an 87Hz tone, so it's likely you're getting some reinforcement/cancellation around that frequency. Moving your head back and forth takes you in and out of that hotspot, and it's quite audible. No tin ears here!

The best sounding rooms are also those with three mathematically unrelated H x W x L dimensions.

Steve F.

[Guest postjob62]

>A good rule of thumb when putting speakers on stands is to

>make certain that the three distances with respect to the

>woofer (up from the floor, to the wall behind them, and from

>the side wall) are all different and mathematically unrelated

>(no whole number multiples). This will spead out the

>reinforcement/cancellation modes over as wide a range of

>frequencies as possible, resulting in the smoothest in-room

>bass response.

>>

>Steve F.

Steve,

When I observe the above "rule of thumb" you kindly put forth, do I correctly assume that the "three distances" you mention refer to the speakers as a pair? That is, that the speakers may be placed symmetrical to each other relative to these three distances as long as the lack of mathmatical relationship among these three distances exists?

In an earlier response in this same thread, Tom said:

"Avoid placing the speakers equidistant floor-to-ceiling, if possible, or equidistant to the side walls."

Likewise, does Tom mean simply not to place the speakers as a pair halfway between the floor and ceiling nor 1/3 the distance each in from a side wall, or does he mean that they should be placed at asymmetrical heights relative to each other and at likewise asymmetrical distances from each side wall?

I apologize for making this seem more confusing than it actually may be, but these posts I had never heard of the "Allison effect" and was of course about to begin building my stands from the material I've collected. Not wanting to attenuate the 4x's very pleasing bass response, I'm trying to get a better grip on this.

I think I will try some experiments tonight (when the wife is shopping) with some small furniture that approximates the projected height of my stands and see what happens. Perhaps then I'll see if anyone is interested in a new thread addressing AR bookshelf size speaker placement. Guess I'm going to need to re-think my 2ax's in my concrete floor basement as well, but for now I'm mostly concerned about the 4x's in my office.

Regards,

Ed

[Steve F]

The three distances from the woofer to the nearby room boundaries refer to each speaker individually. The woofer of the left speaker should be three unrelated distances from the walls and floor, and the woofer of the right speaker should also be three unrelated distances from the wall and floor. Ideally, the left and right speaker should be at least somewhat ASYMMETRICALLY placed in the room, such that the woofer-to-boundary distances are different for the two speakers.

Spreading out the woofer-to-boundary distances over as many dimensions as possible "randomizes" the bass reinforcement modes, thus ensuring that no single frequency or narrow band of frequencies will be unnaturally emphasized or attenuated. Tom's comment about not placing the speakers halfway between the floor and ceiling is exactly the same thing that I am saying: keep everything non-symmetrical (no whole number multiples of distance).

Also keep in mind that after you've moved your 4x's or 2ax's around and made sure that they're in an acoustically-advantageous location, you may think that they've "lost" a little bass response (because a previously unnatural bass hump has been eliminated with corrective placement). If this is the case, you may use your bass control to add in a judicious amount of boost, secure in the knowledge that your starting point is one of essentially smooth in-room response. Really good tone controls, like those in AR's electronics, are made for exactly these reasons. There is no "shame" in using a good tone control to add or cut a few dB to make a good response even better.

It's a good thing to try all this out when you're alone, lest anyone else in the house think you've taken leave of your sanity.

Steve F.

[Guest robobxman]

Just came back to this post. My conclusion the woofer was on "top" is based not only on the badges, but the orientation of the speaker terminal labels. The "T"s are upright when the woofer is topmost and would be upside down if I flipped the speaker over.

If I place the speaker on its side, all is well! However, this makes me wonder how large bookshelves were in the 60s and early 70s. They would have to be quite deep and strong to hold these speakers ... I certainly don't have any in my house that would. Off topic I suppose.