AR2ax (Early) Tweeter Dome Suspension

[ReliaBill Engineer]

52 minutes ago, Aadams said:

I meant, you did a good job, getting them to match.  Paul Desmond sounds good. 

Thanks. I took notes and pictures on the first one. I used a 0.015” feeler gauge around the domes to get them set prior to applying sealant. 
 

I did a test patch of the sealant to see how thick one brush stroke left on a steel plate, after curing. I used a digital scale to measure butyl sealant and thinner. 

The hard part is carrying these back into the garage for cabinet refinishing. I enjoy listening to them.

[genek]

5 hours ago, ReliaBill Engineer said:

I’ve been listening to these a lot over the last several days. I’m not wanting for treble at all. These don’t need an “augmenting” super tweeter. I’ve read that many times from owners of both the 3/3a and 2ax

The preferred add-ons of the period (Janszen and Microacoustics) were not so much about more highs as different highs, or highs in more places. Their goal was to produce a wider dispersion pattern and a more enveloping soundfield. The concept would reach its zenith with speakers like the Bose 901, AR's LSTs and a variety of omnidirectional speakers from others.

Modern super tweeters are all about more on-axis highs, and most of us here don't think very "highly" of them.

[ReliaBill Engineer]

What I’ve found is that these phenolic domes do a very good job of dispersing their output, *if* they are allowed to have more output. The internal batting under the dome tends to suppress cone breakup and distortion. If the domes are allowed to move, produce greater output, 2 things are solved: wide dispersion and ample output. Off axis sound is very good from these. No additional tweeter of any kind is necessary. At 100% position of the tweeter pot, these tweeters overpower the mids. So 85% tweet and 75% mids is good.

[genek]

That's a bit higher than what was typical when those speakers were new, but "typical" is highly dependent on placement and room characteristics.

For dispersion, an easy test is to put on some music with a lot of high frequency content and walk around the room while it's playing. If the "sweet spot" where the sound doesn't change as you walk around seems to extend from one side wall to the other, you're good. This is the test where ARs with dome midranges tend to beat the 2ax with its cone mids.

[ReliaBill Engineer]

My living room is 18x35 feet. Speakers are 8.5 feet apart, center to center, on the 18 foot wall, 3 feet from the wall. I can sit in any one of 4 places and the sound doesn’t change. All 4 seating positions are about 20 feet from the speakers. Speakers are 16” off the floor, tilted back about 10 degrees on stands. 

[rl1856]

Amazing that original AR domes can be rebuilt.

Points raised in this thread bring up several questions:

The response of a 60yr old driver, exposed to the elements for 60yrs, is definitely not the same now as when new.

Restoration of the driver will improve response.  However is the output of a restored driver approximately the same, or different than a new driver 60yrs ago ?  If the output is greater, is there additional strain on the driver, and on fragile 60yr old VC wire ?

Much of what is considered treble response, occurs at frequencies under 10khz.  Given AR crossover and driver design, the midrange contributes a lot more to treble response than most understand.  We know that AR dome tweeters have deteriorated after 60yrs.  How much have AR dome or cone midrange drivers deteriorated after 60yrs ?

 

Thanks !

[ReliaBill Engineer]

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….

[ReliaBill Engineer]

Nice sound! Playing 1960 and 1961 stereo records using a 1961 GE VR1000 cartridge (my redesigned/rebuilt needle) over these 1965 AR-2ax speakers!

 

 

 

 

 

 

 

[Shacky]

I love this early version!

[ReliaBill Engineer]

  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!!!!

 

[ReliaBill Engineer]

Playing a selection from the 1964 Stereo album, Billy Vaughn “Pearly Shells” on vinyl.