RoyC

I have never tried that one, which appears to be primarily lead (80%). I use solder similar to the type mentioned in the Google search response posted above by David ("What kind of solder works on aluminum?"). https://www.google.com/search?q=what+kind+of+solder+works+on+aluminum&source=hp&ei=9ONyZNP0DaqhptQP5_yYsAo&iflsig=AOEireoAAAAAZHLyBA9-G94quj8-OITfb_rq6rph_aai&oq=What+kind+of+solder+works+on+aluminum%3F&gs_lcp=Cgdnd3Mtd2l6EAEYADIGCAAQFhAeMggIABCKBRCGAzIICAAQigUQhgMyCAgAEIoFEIYDMggIABCKBRCGA1AAWABg8iFoAHAAeACAAVSIAVSSAQExmAEAoAECoAEB&sclient=gws-wiz Roy

The leads are definitely aluminum. If you are in the US I can mail you a piece of the type of solder David described above. Send me a forum PM. Roy

The leads of these tweeters are aluminum and require special solder. It runs about $40/roll. E6000 or Gorilla Clear Grip adhesive woks well for the mid screens. Roy

Please don't shim the woofers. I visited with Bill at his place some years ago. At the time he said he uses shims whenever possible. As an aside, he had every part imaginable in that place (including dust caps), and gifted me some nos AR voice coils. Nice guy! My primary reason for my previous post(s) was in response to the curious advice posted earlier in the thread..."please don't shim the woofers". There are more than a few people doing this for the first time, and that wasn't a particularly helpful recommendation, imo. It's hard to believe some of the re-foam disasters I saw at the shop.

Agreed, Pete...until this last batch I worked on. We can put our heads together in a new SA thread. :)

I did to, but it now appears there was more to it. 🙃 I'll post a photo and more information in a new thread. Roy

I know you have experience, Doug. (Sorry if I implied you didn't.) I try to gear my posts toward the neophytes reading the forum...and dealing with a botched re-foam job is very difficult due to the tenacity of new adhesive. Been there, done that... On a completely different subject, I also know you have some experience with the Smaller Advent. I plan on starting another thread on the subject, but after working on a number of SA specimens in recent months, I may be able to shed a bit more light on previous discussions regarding tweeter and crossover differences. I may have missed it along the way, but I never realized there was a 4 ohm and an 8 ohm version of the SA woofer, which could explain some of what we've seen. We can compare notes when I get mine organized. Roy

Happy to be of assistance, Norman... Nice re-foam job! Roy

Hi Doug, Some voice coil gaps are large and forgiving (such as Advent), but others are small and much less so. I have repaired more than a few unsuccessful re-foam jobs due to the difficulty of navigating these gaps. I have been at this for decades professionally, and have had this discussion with some very respected pros such as Bill LeGall of Millersound...who uses shims whenever possible. In our work, along with the small gaps mentioned above, a problem with spider orientation is not as rare as you may think. In this case, using shims will greatly assist in the optimization of the voice coil's clearance to the walls of the magnet. Some spiders are very soft and/or worn which can somewhat increase the degree of difficulty as well. Shims are also helpful when the cone edge is not level with the basket, as in the case of some iterations of AR woofers, when friction allows the cone to be manipulated and centered at the same time. With that said, a practiced hand will likely have a high degree of success with Advent woofers using your method. I also agree regarding the "test tone" method. Might as well just use a battery (though it still won't correct for the issues mentioned above). Roy

These specimens were definitely worked on by someone along the way. -Removable grills were used on 4x cabinets with (much) later serial numbers than these. It is obvious to see where the original hot glue was removed on these. -The split shafts of the level controls shows that the pots were replaced with L-pads or the pot replacements sold by AB Tech (in the 90's). -It is likely the original 4x tweeters were simply replaced with AR-4 tweeters. Cabinet hole dimensions are the same for both models Roy

This comes up periodically. The answer is in the forum Library: https://www.classicspeakerpages.net/library/acoustic_research/ar-9_series_1978-1981/ar-9_series_other/engineering_the_ar-9_by_tim/engineering_the_ar-9_by_tim_5.html Roy

Agreed...I don't recall seeing an AR-4x tweeter with the screen and pad arrangement of the AR-4 tweeter. Additionally, the serial number on the cabinet tag is high enough to be well into 4x production, so it is not likely for these to be early enough to have overlapped with the AR-4. Interesting...

Yeah...still nope. :)) Roy

I would advise against closing off the openings. I've seen pots with melted plastic shafts due to excessive heat from hard use (which is probably the reason AR eventually went to metal pot shafts). Tarnish and corrosion will always be a greater problem than the fibers. Roy

...and the original pots are already vented.

Agreed! Roy

At 1Khz (the frequency at which the stated value of a capacitor is labeled), ESR of decent new npe caps is seldom higher than .5 ohm. It, however, can increase rather dramatically as frequency decreases. This is especially pronounced with lower cap values. The capacitance of higher value npe's will increase as frequency decreases, but ESR is less affected. Unfortunately even though this behavior is the same for all npe's it can vary with era and age, making them much less predictable than film caps. Technically the behavior of new and old npe's can affect crossover points/slopes, and sensitivity. This is further complicated by differences in the behavior of new vs old npe's. While exhibiting essentially the same behavior, older npe caps can present higher series resistance at all frequencies. The effect can be a "warmer" or "smoother" sound for some people. Others may find it to be less "detailed" or "muted" and prefer the boost of new npe or film capacitors. It usually comes down to a matter of preference...especially considering the many additional external variables. In other words, it is entirely possible for someone to prefer the "sound" of the original capacitors over any type of replacement. It should be noted that the vast majority of capacitance (and ESR meters) used by hobbyists measure at extremely low fixed frequencies, and are unreliable when it comes to discerning the above characteristics of npe capacitors. High value npe caps (typically above 20uf) almost always measure on the high side with these meters. (Since film caps vary very little, the basic meters work just fine for those.) Playing with tiny-valued by-pass film caps can be fun and interesting for audiophiles, but are relatively insignificant compared to the obvious measurable variables associated with npe behavior. In light of the above, film crossover capacitors (any type or brand) are extremely predictable, and measure nearly ruler flat across the audio spectrum with barely measurable amounts of ESR at any frequency. These typically result in a brighter/more aggressive effect in the upper mid/lower high frequencies, where our hearing is the most sensitive. Below are Ken Kantor's comments from the link provided earlier in the thread. "Electrolytic cap technology was starting to get good around the time the MGC-1's were built. I have never had to replace any in my pair, but I realize that that might be, to some extent, luck. At any rate, quality speakers made in the 80's should have an indefinite lifetime, provided they were not exposed to really excessive power or ambient heat. Speakers made in the 50's, 60's and 70's a totally different story, and almost always need new caps. I suppose you need to use your intuition, your ears and maybe a good capacitance meter. If you do decide to replace, try to find reasonable matches to the originals, and avoid expensive "improvement" parts. We knew what we were doing when we voiced a crossover, and the parts characteristics are factored into the response. It you replace an electrolytic with a film, for example, you might wind up with a treble boost, or an underdamped resonance." Roy

The AR-5 is an easier amplifier load (8 vs the 3a's 4 ohm impedance), is not as sensitive as the 3a, and will not handle as much power. Even though it is similar, the 5 is also less sensitive than the 2ax. Bass response of the 5 will not be greater than the 2ax, and is somewhat more controlled due to a more sophisticated crossover.

Hey Jim, In the past I've glued small blocks of wood and velcro in the corners to hold the frame in the proper position. Not being a fan of the original snap-in arrangement, or synthetic material, I also use the 3a type of linen (which was also found on the last AR-3's). Roy

Yes...I can repair them, as well as warped and cracked flanges. Roy

One person's "numbness"...Your preferences obviously lean to a more modern sound. It is pointless to get into a debate regarding preferences, especially in light of the comments above. There are many variables involved. A rabbit hole indeed. You've already made the tweeter hotter than it was originally. :) Roy

Agreed...and I would add the AR-11, 12, and 10pi to those options.

AR mechanically contoured the response of all its proprietary drivers to achieve the desired outcome with very simple crossovers. As time went on manufacturers became much more reliant on more sophisticated crossovers. Examples: -The unusually tightly packed fiberglass under the phenolic dome of the early AR-2ax/AR-3 tweeter, AR-3 mid, 2a, 2ax mid cones, and AR-4/4x tweeter cones. -The treatment applied to the 4x tweeter cone. -The fiberglass pads on top of the AR-3/ 3a mids, AR-2ax mid, and AR-4 tweeter. -The foam damping rings on the AR-10 and 12 inch woofers. Early woofers with these had much thinner/stiffer cones than the later foam surround woofers having no rings. -These are in the same category as interesting items you have already encountered regarding the material suspending the tweeter domes. -Other more typical items along the way were changes in the amount/type of cabinet damping material and crossover changes to accommodate changes in driver construction. AR was conducting careful response measurements to achieve design goals. Tom Tyson provided photos at one point showing AR prototypes buried face-up in a field with microphones hanging over them to measure response with no reflections! Recordings of acoustic concert halls were also used as a reference. Much innovation and engineering went into achieving high quality sound from "small" speakers. AR was the first to do this. Bear in mind that better speaker designers of the day were very aware of that era's limitations in recordings and radio broadcasts. To some extent they minimized the typical noise associated with them within the upper midrange, which is a very sensitive area of human hearing. I first saw this mentioned in an Advent publication when introducing the "New " Large Advent as being more responsive to cleaner "modern" recordings. Henry Kloss (co-founder of AR) also made comments in this regard along the way. Also, when these speakers were being made, lower powered amps (often mono), no equalizers, and (obviously) no digital effects were the norm. Two speakers were meant to fill a room, often from a (hopefully very sturdy) "bookshelf". The above are probable answers to some of your questions. You are not the first person to ask them, nor would you be the first to desire a more modern sound. There is a "Mods and Tweaks" section of the forum for these discussions. Roy

These are straight forward ported designs, where tubes of specific dimensions are used to pass certain bass frequencies. All of the aperiodic designs I have seen do not have have a tube as part of its construction. Perhaps the most sophisticated example of an aperiodic vent was manufactured by Dynaudio: https://site.diy-loudspeakers.com/images/datasheets/loudspeakers/dynaudio/VARIOVENT/DYNAUDIO_VARIOVENT.pdf Roy

There is no mystery to be solved. Jab. -The AR labels with the red dots, were placed on the side of the + terminal. -561 is the manufacturer's code, and is found on all AR drivers beginning sometime in the 70's. -The AR-94 and 93 series had a number of variations (thus the "Q" designation of your specimens). Some versions used slightly different woofers in different parts of the cabinet. Based on your photos, your woofers are all original equipment. The person who placed handwritten notations on the labels wisely designated where they needed to be reinstalled in the cabinets. -Forum posts and Library will provide informative reading. -Your suppositions regarding the effects of "time" and construction are erroneous. Genek's suggestion is the best advice you will receive, imo. Roy