AR 4X Dust Cap Question

[shacky]

Just got a pair of 4X's from Narodow. This looks like it's original but why would AR put a porous "see through" dust cap on and AS speaker?

 

[gkimeng]

The woofer in the pics appears to have its surround bonded to the front of the cone rather than the back, which on an AR usually indicates a refoam, but the picture is not quite sharp enough for me to be able to tell for sure. If the woofer was refoamed, perhaps the dust cap was replaced at the same time.

 

[shacky]

Looks like original cloth surrounds. That's why I figure DC must be original too :scratch2:

 

[shacky]

Some better pictures:

 

[joelongwood]

I just looked at the dust caps on my AR4x which have been in my possession for over 40 years now. They have never been touched...........and they look exactly like yours. They are original.
The only difference in my woofers and yours is that my surrounds are brownish in color.
BTW, Shacky......you could set up your own AR Museum at the rate you're acquiring these things.

 

[motorstereo]

I'm presently rehabbing my 4x's and they look exactly like yours including the rust ring around the tweeter. The woofers look exactly like yours including the porous dust cap. No problem in the bass department so I'm only going to redope the surrounds. My original tweeter though had become completely unattached from the metal backing due to the rust. I just so happened to have a pair of klh tweeters from a model 24 and what do you know it's an exact fit. Even the wires were the same gauge and color. Looks like there's a klar4 in my future as I don't believe the original tweeters are worth the effort.

 

[shacky]

Hooked them up for a listen. After listening to my latest 3a project expectations were low. And of course AR of this era continue to amaze me. No wonder they had nearly a thrid of the market back then. These are extremely listenable speakers that I'm tempted to do nothing with - course that feeling won't last

My wife saw them and said she'd like them in her studio.

Aren't the tweeters the same as midrange from 2AX without the fiberglass ring? :scratch2:

They sound better than they have any right to sound. This much bass from this size speaker - those AR folks knew what they were doing didn't they?

Are the woofer's alnico magnets? Anybody have a picture of the driver including magnet they can post?

With sound this good, why would anyone want to econowave these? :scratch2:

 

[RoyC]

.
Aren't the tweeters the same as midrange from 2AX without the fiberglass ring? :scratch2:

Are the woofer's alnico magnets? Anybody have a picture of the driver including magnet they can post?

Hi Shacky,

The 4x tweeters are smaller than the 2ax midrange.

Attached are pics of your era 4x woofer. The dust cap is vented, and the magnet is alnico. Your specimens are original. :yes:

Other than the usual pot issue, the only other concern would be the bond between the tweeter cone edge and basket. It is often found to be detaching, but is an easy fix. If the caps are the 20uf Sprague cans, they are usually in good shape, and not likely to require replacement.

Roy

 

[Bauhausler]

Dahlquist used a porous dust cap on the DQ-10 and DQ-20. The air leakage through the magnet gap may be very small.

I'd change the caps out even if the tweeters still play. I've found 'working' caps in ARs that measured as much as 50% off value. Caps are cheap insurance.

 

[shacky]

Hi Shacky,

The 4x tweeters are smaller than the 2ax midrange.

Attached are pics of your era 4x woofer. The dust cap is vented, and the magnet is alnico. Your specimens are original. :yes:

Other than the usual pot issue, the only other concern would be the bond between the tweeter cone edge and basket. It is often found to be detaching, but is an easy fix. If the caps are the 20uf Sprague cans, they are usually in good shape, and not likely to require replacement.

Roy

Thanks Roy!

Someone has been inside these as they appear to have L-Pads in place. Good to hear about the Spragues. If L-Pads are in there should I add the 25 OHM resistor to make them work more like the original?

 

[RoyC]

Dahlquist used a porous dust cap on the DQ-10 and DQ-20. The air leakage through the magnet gap may be very small.

I'd change the caps out even if the tweeters still play. I've found 'working' caps in ARs that measured as much as 50% off value. Caps are cheap insurance.

Some of the 4x woofers have masking tape on the magnets, presumably to stop air leakage. Others have a porous black plug as seen in my photo, and some leakage past the voice coil is apparent.

When we were putting together the AR-3a Restoration Document over at CSP, http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=4095, we measured dozens of old AR caps with some pretty sophisticated equipment, and found the Sprague Compulytics to have held up very well compared to other AR specimens. In fact, they largely measured better than typical brand new modern electrolytics. It is prudent to use modern film caps when replacing these old timers.

Shacky, the 25 ohm resistor/l-pad combo works well with the 4x. I found the midrange response to be a bit forward with just an l-pad.

Roy

 

[shacky]

Roy,

I do find the midrange a bit forward. Unfortunately when I did my first listen this morning I mistakenly put my receiver on A&B so the 3a's were still playing. No wonder I was so impressed and thank God I didn't do it for long as that was a strain on my 9090DB.

They are still very nice but I think they will be better with the L-Pad toned down and some other tweaks like the seals checked.

.

 

[motorstereo]

That was no strain on your 9090db. The A&B are wired in series unlike most other recievers.
Anyone have any thoughts on getting rid of the original rock wool and replacing it with acoustuff?

 

[shacky]

That was no strain on your 9090db. The A&B are wired in series unlike most other recievers.
Anyone have any thoughts on getting rid of the original rock wool and replacing it with acoustuff?

I had read that driving 2 pair of speakers with the 4 OHM 3a's would put below a 4 OHM load on the amp which is not good :scratch2:

If you do a search over on www.classicspeakerpages.net you will see a ton of information on stuffing. I'll let those more in the know make suggestions. I've heard it both ways - AR designed for the specific particle size and air flow of FG. And appropriate weight (to match dampening of the FG weight) Acousta-Stuf or other will work fine.

The smaller size 4X wouldn't cost as much to fill with Acousta-Stuf.

 

[motorstereo]

Yes on most recievers that would've been a problem. The 9090db runs their A+B speakers in series so the amp sees an 8 ohm load with both 4 ohm speakers running.
I just finished up my 4x recap and decided to stay with the original rock wool. I didn't have enough Acousta-Stuf left over to do them so the rock wool went right back in. Now to hook them em and see how they sound after a recap, redope and retweeter.

 

[shacky]

Did you replace the pots or clean originals? Rock wool I'm told will eat those originals up - high sulfur content.

Sounds like you already buttoned them up so may be moot point. Are you sure it's rock wool and not just yellow FG?

And are the 4X's 4 OHM? This is my first exposure to them.

 

[motorstereo]

I had all intentions of taking the pots apart and cleaning them up but they honestly didn't look bad. I sprayed them out real good and I'm hoping for the best. I saw that that the rock wool isn't good for the pots but what the heck after 40+ years and they're still ok who am I to complain. My ohm meter reads 6ohms so I'm guessing that they're 8ohm speakers. It'll probably be tomorrow before I can listen to them as the mulitple coats of danish oil is still drying. This is my first pair of 4x's as well and I have a nice pair of recapped epi 100's to compare them to.

 

[shacky]

Mine looks like rock wool too. I guess AR used the cheapest stuff they could get on these - or both ours were at a time with the yellow FG wasn't available.

Someone put what look like 20 OHM l-PADS in mine. Now I don't know what to do. I have a couple of old Aetna-Pollak's from my other AR projects I could clean up and put in there. I'd hate to use $15 Ohmites on the 4X's. And 20 OHM is closer to 16 so maybe these L-Pads are OK as far as effects on crosseover freq or midrange forwardness. Heck maybe they do the opposite as far as the midrange effect. :scratch2:

Also see 2 "Dimie" 10 OHM caps in each. Are these any good?

The seal on the woofer wasn't great so I think fixing that up will increase performance and I'll re-seat the tweeter as well.

Here are some more pics:

 

[gkimeng]

Mine looks like rock wool too. I guess AR used the cheapest stuff they could get on these - or both ours were at a time with the yellow FG wasn't available.

According to the lore, this is what happened; AR used rock wool because there was a FG "shortage." The period when this happened seems to correspond to the period in the 60's when industries were scrambling to find replacements for asbestos in various applications. I can't recall any time in the past 50 years when you couldn't walk into a hardware store and pick up a bundle of FG insulation anytime you needed one, but perhaps the "shortage" was for companies needing large quantities.

During the 70's, industrial health and safety considerations caused AR and many other companies to switch to a poly stuffing, but this was not the same as pillow stuffing or currently available acoustic stuffings, and the amounts of these needed to equal the acoustic characteristics of FG or rock wool will jam a classic-era AR cabinet so tight that you won't be able to push the woofer into its opening. FG is the only readily available material that will produce the correct results.

 

[shacky]

Here's what's in mine. My serial numbers are ~201,xxx. Date of drivers is 1968. Tweeters Nov. Woofers look like 24th week.