RoyC
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Posts posted by RoyC
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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
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6 hours ago, bubu91220 said:
I note that over time that the lines of the tweeters are very hard to solder, and I wanted to know that it was there ideal solder. the second problem is the midrange grilles which are partially unstuck. I wanted to know what was the ideal glue to glue these grids.
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
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Please don't shim the woofers.
6 hours ago, Pete B said:I have a pair of LA woofers here that were refoamed by Bill LeGall of Millersound about 6 months
ago and there's no sign of the dust caps being removed.
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.
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6 hours ago, Pete B said:
If you found an 8 ohm SA woofer I'd say that it was probably worked on with a VC replacement or
they mixed up some LA woofer voice coils in with the SA ones. It is in the "engineering" sales
literature that while they SA maintains the same F3 as the LA they lowered the impedance to 4 ohms
in order to keep the system voltage sensitivity as close to the LA as possible.
However, even the LA is lower than 8 ohms with the DCR usually measuring under 5 ohms.
When I worked on a few SA woofers I was surprised how similar, if not the same the magnet pole
piece, VC were to the LA, probably a parts commonality thing for mass production.
I repair two SA woofers here with some notes:
https://audiokarma.org/forums/index.php?threads/small-advent-woofer-repair-some-measurements.819443/
I measured a DCR of 3.3 ohms for the SA woofer.
Agreed, Pete...until this last batch I worked on. We can put our heads together in a new SA thread. :)
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8 hours ago, Doug G. said:
I thought the woofers are always the same but they changed the tweeter to use the same, larger magnet version and made a crossover change to match the efficiencies of the tweeter and woofer in the Smaller Advents.
Doug
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
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2 hours ago, Doug G. said:
So, I am not writing from a neophyte perspective.
Doug
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
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Happy to be of assistance, Norman...
Nice re-foam job!
Roy
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14 hours ago, Doug G. said:
Well, as I have written quite a few times before, the VC is already centered at the spider in the typical driver unless there is a problem with the spider which is rare. The only thing that needs to be done is to ensure the VC stays parallel to the magnet/pole piece, all along its length, during the refoam and this is easily accomplished by pushing down along the perimeter of the cone all the way around as the glue sets. This guarantees the cone is parallel to the pole piece because pushing on the perimeter, all the way around, slightly biases the VC into a "slanted" position and it would rub on the pole piece if not parallel/centered.
I have done it this way during my whole long-time experience with refoaming drivers and have never had a failure. The procedure doesn't have to way more complex than it need be. The tone thing is even unnecessary.
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
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19 hours ago, ReliaBill Engineer said:
Pot looks different from pics I’m used to seeing. Splined, split shaft? And removable grills? Treated woofer cone?
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
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5 hours ago, lance G said:
No stuffing ever installed from new, and not required ?
This due to only very low frequencies and a requirement for large air volume movement in this area of the cabinet/s.
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
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38 minutes ago, genek said:
These look more like the earlier AR-4 to me.
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...
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1 hour ago, Aadams said:
Provided no new developments in the last few days, the answer is no. I have had one with the same problem in a box for several years waiting for RoyC to say he could fix it.
Yeah...still nope. :))
Roy
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On 5/9/2023 at 6:50 PM, tripleguy said:
Yes
I was just wondering if you could close off the opening to keep mineral fiber out of them. I did apply a thin layer of silicon already. Pretty thin.
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
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...and the original pots are already vented.
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16 hours ago, AR surround said:
Glad to hear that things have ended up well. If you like the way your recapped speakers sound, you might not want to challenge fate and drive yourself crazy in the process.
Agreed!
Roy
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On 5/5/2023 at 7:03 AM, AR surround said:
Other's who have measured that ESR might be able to answer that question. However, as implied in other posts above, you should be able to effectively raise the ESR of those series capacitors by using the attenuation switches. A 3dB reduction is large and audible. A 6dB reduction is huge.
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
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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.
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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
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1 hour ago, Bogden said:
One tweeter broke in shipment,would they be worth refurbishing
Yes...I can repair them, as well as warped and cracked flanges.
Roy
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2 hours ago, ReliaBill Engineer said:
That’s why I can hear a certain “numbness” of detail in these. The mid driver isn’t capable of reproducing it. I’m used to hearing that detail. When I switch from “Speaker A” to “Speaker B”, I can plainly hear the difference.
...it’s a rabbit hole journey.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
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1 hour ago, ar_pro said:
It's always seemed to me that if one wanted a more modern, slightly less first-generation sound from an AR speaker, the AR-91 and AR-92 are at their disposal.
Agreed...and I would add the AR-11, 12, and 10pi to those options.
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17 hours ago, ReliaBill Engineer said:
Is it used to add dispersion? Tame a sizzling midrange? Acoustic (air) impedance matching? Or….add mystique?
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
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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
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3 hours ago, Jab said:
This is a mystery trail.... kind of fun.
Made in USA or not, I think these speakers are nothing particularly special. The cabs are solid, worth an upgraded set of drivers if a suitable match can be found.
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
question about servicing old AR3 AR2 drivers
in Acoustic Research
Posted
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