ReliaBill Engineer
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Posts posted by ReliaBill Engineer
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On 6/30/2023 at 5:57 PM, RoyC said:
The sealant is not at all "thick" nor is it "messy" if properly applied. In fact, it is deliberately very thin to act as a supplement to the original (which did not magically go away). It remains tacky so it will not form an additional membrane, which has the potential to affect performance by altering mass and compliance. The high percentage of toluene in it can also serve to loosen any hardened original sealant. As for not liking the way it "looks"...well these are, after all, AR speakers. Eye of the beholder, etc.:).
Much time and measurement (primarily Fc and Fs) went into developing the formula, along with some information from Roy Allison (through Tom Tyson). It should also be noted that much experimentation was conducted with various membrane-forming materials beforehand.
Roy
“From pics I’ve seen, the vintage_AR dope is thick and messy. It only needs to be thick enough to fill in the very small pinholes in the fabric surround. It needs to be thin enough not to alter the ability to flex; you don’t want to alter the woofer performance. Personally, I don’t like the wet-looking dope showing on the outside of the surround. It never seems to look professional.”
As you see, we both said the same thing here. I’ve seen many pics of this toluene-based dope applied, on FB groups and in SH, VE, and AK forums. Just looks unsightly to me. Certainly quite a ways from original.
Don’t get me wrong, I tried many formulas myself, practicing on fine cloth, parchment paper, on bare steel, to get the formula to produce an extremely thin “wash” on the fabric, and also a primer/cleaner on the cloth surround prior to application. The butyl-based formula I wound up using is 95% by weight thinner/solvent. It only leaves an extremely thin sealant layer that is resistant to decades of ozone, heat, flexing. And, it doesn’t attract dust, poly fill, fiberglass or rock wool fibers, since it’s not tacky or sticky. It’s so thin that you can’t tell it has been applied at all, by looking at the front (outside) of the surround. I’m very happy with the results. I used about 50/50 Stoddard Solvent and Naphtha. Stoddard is more aggressive than Naphtha, but Naphtha is slower to evaporate. It makes the butyl easy to apply as a “wash” with a brush in a very fine layer, then levels nicely.
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Playing a selection from the 1964 Stereo album, Billy Vaughn “Pearly Shells” on vinyl.
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You do know, don’t you, that if you rebuild the tweeters, and the output increases, that you have a pot you can use to turn them down?
Just a thought….
My rebuilt tweeters output more than the midrange, and likely more than originals. So I know I’m getting every bit of sound they have to offer, from 5K up to at least 15K. I turn mine down to 80% to compliment/match the mid and woofer. I can tell the difference between using different cartridges, such as the V15V-MR and the Pickering XV15 1200E. Before, the high end just wasn’t there, so it didn’t matter what cartridge I put on my tonearm.
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From pics I’ve seen, the vintage_AR dope is thick and messy. It only needs to be thick enough to fill in the very small pinholes in the fabric surround. It needs to be thin enough not to alter the ability to flex; you don’t want to alter the woofer performance. Personally, I don’t like the wet-looking dope showing on the outside of the surround. It never seems to look professional.
Before applying clear butyl membrane:
After applying clear butyl membrane to the back side of the surround:
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On 6/12/2023 at 7:41 PM, crumpets said:
Ok, good one. Has anyone had success with any alternatives to the cloth surround sealing product offered by vintage_ar on the bay, or is this still considered the best option? Being an ar enthusiast in the southern hemisphere sure has its disadvantages, and postage is one!
I don’t know what vintage_AR uses. I used an extremely thin membrane of clear butyl rubber applied to the backside of the surround, so it isn’t visible.
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“I learned 30 years ago not to put aluminum *anything* inside cabinets, big or small. It colors the sound. The foam without the aluminum tape would be good. On my small Realistic speakers, i used torn up polyurethane foam from a MyPillow that I don’t use. It works well for cabinet damping.”
Inside. Pretty clear, really. Why the skepticism?
Im not talking about the cabinet, whether ABS, Aluminum, MDF, particle board, solid oak, or other.
In a small speaker (our subject here) I was doing some experimenting over 30 years ago, on a pair of Realistic speakers. I bought them for the walnut veneer cabinets, just $40 for the pair. Cheap 5-1/4 woofer and paper tweeter, sealed box. I installed a Peerless mid-woofer and a German polycarbonate dome tweeter. There was no batting or damping inside these little cabinets. They sounded good with the new drivers, but had a boxy/wooly/chesty coloration.
So I tried different batting inside, and some diffusers. I tried the aluminized pipe/duct insulation. It colored the sound drastically. Hard to describe, but very audible. Then I tried aluminum honeycomb used inside the wing sections of the F-14, as a diffuser. It really colored the sound! (I isolated the honeycomb pieces in polyurethane foam.) Then I tried aluminum angle pieces; that was even worse! I tried thin pieces of aluminum sheet metal, but I could still hear coloration. Aluminum rings from the back wave.
Of course, I concluded that none of those ideas were good. I wound up using 2 small squares of rubber carpet backing (excellent sound deadeners!) and torn up pieces of polyurethane foam. Later, I drilled 1/4” holes in the rear to effect an aperiodic damped enclosure. I used a single order Equal-Compromise network. The end result was a neutral sounding small speaker with fast and articulate bass down to 45 Hz, and a nice level of detail and great dispersion. Rubber surrounds stand the test of time!
Small speakers can be a real challenge, being very revealing of flaws and cabinet damping.
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I learned 30 years ago not to put aluminum *anything* inside cabinets, big or small. It colors the sound. The foam without the aluminum tape would be good. On my small Realistic speakers, i used torn up polyurethane foam from a MyPillow that I don’t use. It works well for cabinet damping.
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Mine takes about 1-2 seconds to return. If I hold it in for 5 seconds, it still takes the same amount of time to return. Here, I may not have pushed it “in” far enough. But I can see and hear ample evidence of a good seal.
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Admittedly, I used clear polyurethane and a small artists brush to apply it on the corrosion prone areas of the pots. The brass rivet heads that clamp the resistance coil, the center rivet and plate (but not the outer contact trace), and the 3 terminals, sealing them from moisture. The resistance wire I left alone.
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Not so sure. If it’s truly sealed, pushing in on the woofer cone compresses the air inside the cabinet. Air is a spring. The compressed, springy air should push back on the woofer cone with the same force you used to compress it.
If there is an air leak, (small one) pushing on the cone will push air out of the cabinet. Releasing the cone will cause a vacuum that will slow down the return of the woofer cone, as air is sucked back into the cabinet. -
I don’t understand the question. Solder? Grids? Tweeter rows?
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I decided to remove the red damper dots. I just sliced them off using a razor knife. After extensive listening, I’m thoroughly convinced they aren’t necessary. The 4 notches in the faceplate have to be filled in, but all that’s needed is the clear butyl rubber sealant around the dome perimeter, and on the faceplate to seal out dust. The sound is very clear, focused, articulate, coming from the dome tweeters.
I thoroughly enjoy listening to these!
I have one original grill sitting in place, to see if it would “grow” on my wife. Nope. We’re going with black grill cloth and the brass early AR-2ax badges. I did a sample “stretch” of the black grill cloth, and I must say, it looks very good! Similar to later AR models. Looks good with the semi-gloss cherry veneer.
Below is how the speakers sounded when I first got them. Tweeters and midrange drivers working. Pots worked. Major difference!!!! -
Pot looks different from pics I’m used to seeing. Splined, split shaft? And removable grills? Treated woofer cone?
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Nice sound! Playing 1960 and 1961 stereo records using a 1961 GE VR1000 cartridge (my redesigned/rebuilt needle) over these 1965 AR-2ax speakers!
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On 4/6/2023 at 3:48 PM, JohnVic said:
But the NAD 7080 will outperform any receiver in the so called stereo wars of 1975 to 1985 and certainly sounds vastly better than any receiver I have heard in recent times
I beg to differ. Spec for spec, sound for sound, feature for feature, all discrete preamp and amp. Separate power supplies for preamp and amp. 93 W/ch at rated specs, 185 w/ch long term into 4 ohms, 200 w/ch long term into 2 ohms. +/- 0.25 dB RIAA. These fly low under the radar. I have 3 of these. I bought it in spring of ‘81. In constant use since then; I’ve replaced the power switch. It’s powered 901s, Apogees, KEF 105.2, Quads, MMGs, B&W 801s. Designed in USA, made in S Korea. Sherwood S9600-CP. I bought 2 more a couple of years ago, both less than $50 each; both “as is not tested,” and both work perfectly.
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Well, my dad has a great memory. Using his 1964-1967 records, the same Shure M44C cartridge and NOS stylus, I played his records for him on these 2ax speakers. I turned the tweeter pots down a bit, to 75% and kept the mids at 75%. His comment was that that’s the sound he remembers. I give that a 90% grade for being accurate. He doesn’t miss much, even at 93 years of age.
As for original drivers, the very best one can do is get original AR speakers stored and used under ideal conditions. Low humidity, not damaged, stored in an environmentally controlled space. That is these speakers. Kept in the original owner’s Denver CO living room for 58 years. Placed on their sides in a built in bookshelf. Sold to me by the owner’s son after his father passed away in February of this year.
The increased output of the tweeters is due to my replacing the 4 yellow polyurethane foam dots. The yellow liquid foam was applied to the top of the dome, the steel faceplate, and also on the voice coil windings down in the gap. When I applied the red butyl elastomer, I only applied it to the dome edge and to the faceplate. It’s a gel, not a liquid. So I didn’t apply it to the voice coil windings. Then, like at the AR factory, I applied the clear butyl rubber film on top of the suspension dots and around the dome. So these domes have more compliance to move.
It has the same wires, same voice coil, same dome, same gap, same magnetic circuit, same gap vertically as the original mount.
I have no reason to believe the midrange has changed its character in the last 58 years. Just like I don’t think the cabinets have changed any. So as I adjust the mid pots to compliment the woofer output, I’m getting the exact same sound as 58 years ago. Then as I adjust the tweeter pots, I’m getting the same sound as 58 years ago; but at 85% on the pot, my output is louder.
The most accurate comparator I have is my dad. If someone has a better method to compare to factory new, I’d like to hear it….
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Using modern drivers, I think you’d have to use high and low pass filters to shape modern driver outputs to roll off their normally flat response. Or, use inexpensive drivers for mid and tweeters. I’m talking 1970 and older AR sound. It would be pretty difficult to make an old wineskin using new glass bottles, for 1976+ AR sound.
Substituting a new driver for only 1 in an older AR speaker is certainly doable. Maybe 2. But not all 3 in a 3-way design. Matching Sound power response is only 1 aspect. Each driver has its own voice, and matching that with a modern driver would be difficult. Like Bob Carver matching voices of amplifiers, only more difficult.
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I don’t mess with the pots. They stay at 85% tweeter, 75% mid.
Detail is not power response. It’s the ability to resolve slight variations and frequency mixtures in the signal from the amplifier. That detail and ability to resolve small nuances won’t show up in a sine wave sweep. So the pot has no bearing in resolution, just in relative power output.
My “other” hobby has been collecting vintage cartridges. I’m used to being able to swap cartridges and hear the differences. I have 160. I can hear differences in ADC styli, or Empire carts, or between the V15V-HE and V15-IV HE. Or an ADC 10E MKIV and MKII. But with these AR-2ax’s, that gets very difficult. I love the sound I’m getting, great for enjoying music, but not for enjoying different sounds from different transducers. Hence, why I said I “crave” more detail.
My main speakers are the 1989 Polk RTA-8Ts. Not big. But unique in the Polk line of that era. 2 midwoofers (MW) in parallel, with no crossover tricks to use both for bass, 1 for midrange duty. Ported, no PR. I installed the updated tweeters, but stock other than that. No XO rebuild, no recap. The parallel MW in D’Appolito vertical arrangement (MW-T-MW) resolves detail exceptionally well. Great imaging also.
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2 hours ago, Aadams said:
OK here is the full three pages from 2012. It is informative, entertaining and lots of words.
Yikes! Volkswagens, Newton, “crude vs simple”, sealed vs ported, 1% caps, etc.!
I’ll just accept that the fiberglass batting is used to damp “rough edges” at the roll off higher frequencies.
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4 hours ago, Aadams said:
It is not the mid driver but your span of control. You have zero control over 3 1/2 octaves of mid range starting at 200 hz, while using the mid pot is a gross adjustment of the entire range from about 2000hz to 10khz. You probably need finer adjustment and may be able to get it with your preamp tone controls. A 10 band graphic equalizer would probably give you the single nudge you crave.
Edited to reflect Early 2ax crossover frequency.
The XO to the midrange is at 1400 Hz, isn’t it? At 6 dB/ octave, the mid still has output at 700 Hz. So it carries output 700-8000 Hz. That’s where a great deal of detail is produced. The cartridges I’m using are known for their detail retrieval. 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.
Just an observation. I could correct it without making a visible difference in the speakers. But it’s a rabbit hole journey.
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Thank you! Makes sense.
AR went through a lot of trouble to add the screen and pad, so I’m not going to mess with success. But I was curious. Having said that, I do crave a bit more mids detail than these offer. But that isn’t possible without molesting these and replacing the mid driver.
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Is it used to add dispersion? Tame a sizzling midrange? Acoustic (air) impedance matching? Or….add mystique?
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Anyone know why AR chose to put fiberglass padding over the paper cone midrange? Is the reason documented anywhere?
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To answer my own question, the foam ring is soft polyurethane foam. I guess to somewhat damp a possible source of distortion near the voice coil. Flexing of the cone?
Sacriledge. AR93Q
in Acoustic Research
Posted
Interesting topic and comments here. I’m sure a great many others have had the same thoughts about using new drivers to replace legacy AR drivers, because they fit.
In 1982 I rebuilt my dads Wharfdale W70Cs. When I removed the rear panel, I saw where he had sealed off the port by glueing a block of plywood over the hole from inside of the cabinets. They never sounded correct; chesty, wooly bass. Bass reflex woofers truly do not sound correct in a sealed enclosure! Once I removed the wood blocks, the bass sounded so much better!! But I still completed the rebuild, new crossovers I designed to perform well with the new drivers.
Bass reflex woofers “can” be made to sound good in a sealed enclosure, if you have the modeling software and test equipment on your bench. It’s definitely NOT a plug-n-play scenario, though.