AR 1 question

[DKinYORKpa]

A fellow at AudioKarma sent me here! I just acquired two AR 1 speakers. Here's a pic of serial number 05485 :

My question is about the cut-outs in the corners of the tweeter. Are they correct? While stuffed with insulation, they don't seem particularly air tight. My other one is serial number 4287 and is identical.

[ra.ra]

Hi DK, and welcome to the CSP forum. Your AR-1 speaker looks to be in great condition, and yes, that square cut-out is the original configuration. I am unsure why this was not a circular cut-out, but you should know that this smaller (Altec) driver has its own enclosure which is separate from the remainder of the cabinet interior volume, which is a sealed compartment for the woofer performance. In the pic attached, you can almost see the plywood box that contains the Altec driver. 

[DKinYORKpa]

Hi......You are correct.......Upon closer examination, there is a separate enclosure for the tweeter. (I hadn't removed the fiberglas around it.) On the other cabinet, (the one pictured), it is still unopened and it fails the "seal test" that someone at AK described. "push in on the woofer cone and it should slowly recoil" It springs back at the same speed as the woofer that I've removed. And FWIW, there is a 1578 stamped in ink on the baffle of the ser. # 4287 cabinet.

[genek]

That's not really an enclosure for the "tweeter," which is actually a full-range driver used for mids and highs. It's an indentation in the enclosure for the woofer. The woofer is acoustic suspension that requires a sealed enclosure. The other driver is not

This the enclosure that the WE 755a was most commonly used in during its heyday. Anyone over the age of 50 or so will probably remember seeing something like it in their schools when they were kids.

[ar_pro]

That's a very nice find; intact AR-1 systems are becoming scarce - congratulations!

Have you tried playing either speaker? If so, how did it sound? What prompted you to remove a woofer?

From the Restoring The AR-3a guide:

 

[DKinYORKpa]

"If so, how did it sound? What prompted you to remove a woofer? "

My first listen was on a Pioneer Elite with a CD player. They sounded good. I removed the woofer to check out the crossover. The 24 uF big cap box measured 29 on my Sencore. Not bad, but I plan to leave it in place, disconnect, and strap modern ones to it. The grille cloth/frames are not usable, IMO, so I'm going to make replacements with the oft recommended linen. (I'll keep the originals wrapped and marked for my estate sale) The one grille cloth was attached to cardboard exactly like picture frame mat board and was being held up with carpet tacks. After removing tacks, I could see that half the thickness of the mat board was glued to the speakerboard at spots. It looked like it was reglued at one time, because it was not just the 6 blobs of glue like the other pictured cabinet. Glue was everywhere. I spent 4 hours yesterday with acetone to get it clean. The other grill was glued/stapled to 1/8" masonite. The glue had failed in the past and the grille with the cloth nicely flexed out. Both cloths are spotted/moldy,etc and frayed too much on the edges to reuse.

[JKent]

Welcome DK! As you probably know, those speakers are very collectible and valuable. So proceed with caution!

MOST IMPORTANT: That information about Permatex in the AR-3a is outdated and should NOT be followed. Permatex will gradually cure or harden and ruin the woofers.

The good news is, CSP/AK member RoyC cooked up some butyl sealant that is exactly like the original. You could send him a PM or buy some from ebay seller Vintage AR.

Keep us posted!

-Kent

[DKinYORKpa]

eBay seller  Vintage AR   doesn't come up.

[JKent]

1 hour ago, DKinYORKpa said:

eBay seller  Vintage AR   doesn't come up.

Google "ebay seller Vintage AR"

Or click http://www.ebay.com/itm/ACOUSTIC-RESEARCH-CLOTH-SURROUND-WOOFERS-SEALANT-KIT-ALSO-KLH-/162184720559?hash=item25c2f670af

[DKinYORKpa]

Thanks....I ordered it.

[VintageMan]

Nice find, enjoy!

[owlsplace]

5 hours ago, DKinYORKpa said:

Thanks....I ordered it.

Yes, welcome and very nice speakers.

Because of the rarity of these I would get more input before making changes, including doping the surrounds. There are several schools of thought on this procedure.

Roger

[JKent]

4 hours ago, owlsplace said:

Because of the rarity of these I would get more input before making changes, including doping the surrounds. 

I second the motion 

[DKinYORKpa]

Quote

get more input before making changes, including doping the surrounds.

Chime in.....I do want to do the right thing.......As I said, on the unopened cabinet, the woofer cone springs back to the touch just like the woofer that's removed. Is this not a valid test?

[owlsplace]

5 hours ago, DKinYORKpa said:

Chime in.....I do want to do the right thing.......As I said, on the unopened cabinet, the woofer cone springs back to the touch just like the woofer that's removed. Is this not a valid test?

Maybe TomT will chime in ... yes, missed the previous comment on the push-test -- sounds like a fail if the rest of the cabinet is properly sealed.

Roger

[tysontom]

17 hours ago, owlsplace said:

Maybe TomT will chime in ... yes, missed the previous comment on the push-test -- sounds like a fail if the rest of the cabinet is properly sealed.

Roger

An air leak can also occur as a result of a cabinet leak, so that possibility should be eliminated before putting any coating on the surround.  Nevertheless, judging by the serial-number range and from the dark image, it appears that the woofer surround on this speaker in question is one of the early "pleated" versions, and this type is much more prone to air leaks around the surround than the later half-round surround.  This surround may need treatment.  

AR-1 (internet picture) of pleated surround and felt dust cap.

--Tom Tyson

[DKinYORKpa]

OK, I took a close look at that pleated surround. Holding the speaker up to the light, I felt like I was looking thru a fine sieve. Then I placed a pile of fine saw dust on a piece of paper and held it under the surround. Using compressed air (very low pressure), I blew air at the surround and the sawdust blew away. So clearly that pleated surround is completely porous. Then there was a factory coating on this that has completely degraded? And the above prescribed coating will reseal the surround? And not affect its flexibility?

[RoyC]

25 minutes ago, DKinYORKpa said:

Then there was a factory coating on this that has completely degraded? And the above prescribed coating will reseal the surround? And not affect its flexibility?

There is nothing better for this application (I make the compound for "Vintage AR")...though I doubt the original coating is completely degraded.

You can send me a PM if you have questions.

Roy

[tysontom]

On 9/5/2016 at 0:06 PM, ra.ra said:

Hi DK, and welcome to the CSP forum. Your AR-1 speaker looks to be in great condition, and yes, that square cut-out is the original configuration. I am unsure why this was not a circular cut-out, but you should know that this smaller (Altec) driver has its own enclosure which is separate from the remainder of the cabinet interior volume, which is a sealed compartment for the woofer performance. In the pic attached, you can almost see the plywood box that contains the Altec driver. 

The Altec Lansing 755A 8-inch driver used in the AR-1was an open-back driver (i.e., it is not sealed on the back) and the square cut-out on the AR-1 cabinet was designed by Edgar Villchur and Henry Kloss to allow an opening to the back of the speaker, but fiberglass (or Kimpac in early models)  was placed in the square openings to prevent the box pressure behind the driver from impeding the proper response down to 1,000 Hz, and to prevent any back wave from significantly interacting with the direct output of the speaker.

 

A circular portion was routed out to allow the 755A to be recessed in the cabinet face, and Kloss was probably responsible for this design element.  The box for the 755A was carefully glued and sealed to prevent any type of air leak from within the main part of the enclosure.  This design element was actually well-engineered, as the AR-1 had very clean, uniform response in the midrange and treble, but the treble dropped off above as a result of the natural roll-off of the 755A.  Note that the 755A did have a decoupling section to the cone that improved the high frequencies, allowing the smaller portion to continue to respond to higher frequencies. 

Villchur and Kloss chose the Altec Lansing 755A because it was actually the smoothest full-range speaker available at the time that could be used down to 1000 Hz with the AR-1W woofer.  There were many cone tweeters and horns available, but all had some sort of issue that prevented clean sound reproduction.  The Ionovac tweeter showed promise, but it was somewhat unreliable and it was costly.

Although Edgar Villchur was responsible for the acoustic-suspension principle and the AR-1 speaker itself (the box size and shape, crossover, driver recessed mounting and so forth) Henry Kloss is credited by Villchur as being 75% responsible for the production design of the AR-1 itself.

—Tom Tyson

 

[ra.ra]

Thanks, Tom, for that detailed explanation and the terrific pics. That upper box enclosure for the 755A appears to actually be two "concentric" boxes of different depths and different square dimensions as well. That's a lot of small pieces (10?) to fabricate into an air-tight compartment. I assume the 755A was held in place with only wood screws (no room for T-nuts!) at the four little crescent shaped shoulders from the original routing of the baffle. 

[tysontom]

20 hours ago, ra.ra said:

Thanks, Tom, for that detailed explanation and the terrific pics. That upper box enclosure for the 755A appears to actually be two "concentric" boxes of different depths and different square dimensions as well. That's a lot of small pieces (10?) to fabricate into an air-tight compartment. I assume the 755A was held in place with only wood screws (no room for T-nuts!) at the four little crescent shaped shoulders from the original routing of the baffle. 

The AR-1 was fabricated using both a 3/4-inch top panel and a 1/2-inch inner panel to accommodate the 755A, thus the appearance of multiple boxes.  AR-2's also had this type of baffle, but by 1965s, AR had gone mostly to a single 3/4-inch panel on the front.  The 755A did use wood screws, but it was one of the few AR drivers to be mounted in that fashion.  Note the early use of slotted machine screws for the woofer.  All of the AR-1/AR-3 cabinets had nine internal braces.  

Note that the 755A was a 4-ohm speaker (as was the 728B on which the AR woofer was designed), and thus Villchur and Kloss settled on 4-ohm impedance for that system.  There may have been other reasons, but the 755A and 728B, both Western Electric designs, were 4 ohm impedance.  The 755A dates back to at least 1947, maybe a bit earlier.

--Tom

[DKinYORKpa]

Thanks for the info........FWIW, I just opened up the higher serial number cabinet. While the earlier numbered one had a single cap can with three 8 uF sections, this one has 2 cans tied together that don't match in appearance. The one measures 11.5 and the other 10.4..... I'm used to seeing values go up (On the other one, it measured 29 uF)........Just to be clear, I do want 24 uF, correct? 

[DKinYORKpa]

Here's a view of the cabinet with 2 different cap cans on top of each other. I guess they were 12 uF each but they had to use a slightly thinner one for clearance of the bottom of the speaker?

[DKinYORKpa]

OK, the speakers are finished! They sound good, but I'm no audiophile. Now I'm afraid to crank them too much, but I had them loud. Too loud for my wife anyway.  I don't want to say that my large Advents are better, just different. And I'm not afraid to push them. So anyway, here's the grille cloths that came with them:

They match fabric-wise, but are not usable. They have a vertical gold thread running them. I'll keep them with the speakers for any future sale or my estate sale! One was on 1/8"masonite and the earlier one on thin cardboard, half of which was glued to the baffle board. I send away for that standard AR cloth but it was to close to the white paint, IMO. My new grille frame is poplar plywood a little thinner than 1/8". I adhered a cloth from AES that I like. Don't scream; it's quickly reversible. I sprayed the outside with flat black paint.

Since the frames flex into the upper and lower grooves, I cut the long sides to precisely tight with the fabric pulled around.

There's velcro that grabs only in the middle, the other pieces don't bite. I was able to easily remove the grilles with a very thin piece of metal.So here's the finished look. For the paint, I just scrubbed it good with cleaner. No point in stripping the paint; it's been there a long time and there's no walnut there.

 

[owlsplace]

Wow, I'm amazed these are getting air time -- maybe not audiophile but definitely an aficionado -- jolly good show

Roger