AR92 dustcaps, crossovers and veneer - help please

[npeters]

Hi - Greetings from Canberra, Australia. 

I just picked up a pair of Acoustic Research AR-92 speakers, with consecutive serial numbers for almost nothing. They are in reasonable aesthetic condition, and should clean up nicely for WAF purposes.  I have read that these have a frequency response of 32-20,00 hz, and 200 watts power handling capability

The dust caps have disintegrated, but the roll surrounds look OK to me. Can anyone advise me the material type for the dust caps (fabric? solid paper? metal?), and hopefully the size - I can't find my measuring calipers to estimate the diameter I need. I will carefully vacuum out any debris in the VC gap when I start on the repair process.

Also, what is the best sort of glue to use for the dust caps? I will buy glue with the roll surrounds sold for them, but is there any particular type to use for the caps?

The "acoustic blanket" around the tweeter and mid-range has gone, I have read that black air conditioning or heater intake filter material is good for this replacement use, but any advice is welcome.

Advice regarding the crossovers for a rebuild would be really helpful. I believe that they crossover at 700hz and 7,500hz. Is there a schematic available for these units here? The switches on the back for -3 and -6 dB for the tweeter and mid-range seem to be stuck in one position - should I blast them with contact cleaner?

Is the veneer on the AR92s real wood or is it vinyl?

One last question - should I bother with new ferrofluid?

Once sorted, I will replace the grille fabric.... I also scored 2 x 16 foot multi-braided cable as interconnects for them, so I am pretty darn happy.

Cheers, norm

[ar_pro]

Hi, Norm -

The original dustcap would have been fabric, and the finish is walnut vinyl. The switches on the AR-92 are very robust, and usually trouble-free; contact cleaner could help to unfreeze them.

The foam inserts that fit around your tweeter & midrange are frequently missing, or have just dissolved from age; good ones occasionally turn up on eBay, but they can be pricey.

Best of luck with your new speakers!

 

[JKent]

Welcome Norm!

I hope some other members are more on top of this topic than I. I did refurbish a nice pair of 92s for a fellow member a couple of months back but did not keep adequate notes.

The dust cap was solid paper as I recall. You can use a paper or felt cap. I don't think it matters--just not a porous cap. Size is not that critical as long as it's a bit larger than the originals. Glue them on with white PVA glue. I like Aleene's Tacky Glue but that may not be available in Oz. Elmer's glue maybe.

I used some foam speaker grille material for the rings around the tweets and mids but I'm sure A/C filter or foam vacuum cleaner foam filter will work. Or just leave them off.

Oh! Just got a pop-up that says ar_pro has responded. Looks like he answered most of your questions.

-Kent

PS: Just looked at the schematics ar_pro provided. The big cap in the ones I worked on was 80uF, not 100. And there was a 24uF an 8 and a 4. No 40uF. Best bet is to open yours up and see what's inside. The schematics shown are for the 91, which supposedly had the same xo as the 92 but the 92 I worked on was different.

The dust caps are cloth, but non-porous.

 

[ra.ra]

Welcome to CSP, Norm. There seems to be continual interest in the AR-91, but the 92, despite being an excellent speaker model, just doesn't get nearly the same attention. Kent is correct about the cap values as the drawing and parts list attached attest. Also FYI is another x-o pic.

[ar_pro]

Yep, yep, yep...my bad!

Kent & ra.ra are correct - the values are different in the AR-92.

[JKent]

On another point...

I wonder what's going on with your woofers. I've never heard of dust caps disintegrating and I'm pretty sure that despite how the foam surrounds look, they're probably shot.

And regarding the caps; the 4uF & 8uF are Callins PVC and they are notorious for leaking. Replace them with film caps. The cans OTOH may still be good. Do you have a C tester? Of course you may want to replace them just to be on the safe side. I'd use film for the 24uF and let your budget decide whether to go with film or NPE for the 80uF. The only advantage to film is it will last virtually forever, but film caps that size are pricey (about $20-$30 USD each or more, vs about $1 USD or less for NPE).

-Kent

[npeters]

I am guessing the a previous owner has replaced the surrounds. They are in excellent condition. I am guessing the had a go at the dust caps but gave up.

I am interested in the AR92 veneer too - is it wood or vinyl? if vinyl, is it easy to tidy up general scratches, etc. Or if I am going to keep them should I strip them back and re-do them in real wood veneer? Two sheets of 2400 x 300mm will easily do a pair, and with a bit of TLC to the brown painted bits they should come up OK especially with new grille cloth?

Here's the woofer - both are in the same condition, and below that is a poor image of them minus the grilles.(sorry about the phone camera quality)

[JKent]

1 hour ago, ar_pro said:

the finish is walnut vinyl.

 

[KlausDK]

I had a set of AR-92 for refurbishing, I cut the foam for the acoustic blanket myself from a roll of ½" thick speaker foam, I think I bought 1 square meter.

BRgds Klaus

[ra.ra]

Your speakers look good, and I suspect you may be correct about the woofer status. Those surrounds look relatively new, but there is no good reason why the dust caps were never replaced. In fact, having the voice coil exposed like that is not good at all - - - there is all sorts of opportunity for dust, pollen, and assorted unwanted debris to find its way into the VC gap. You need to apply some non-transparent duct caps - - looks like Klaus might have some flat ones on his 92's - - but first be absolutely certain there is no residual debris lingering about. Time to get out the vacuum hose!

About re-veneering, that is your choice, but it is a substantial undertaking. Unlike the AR-91 with its angled top corners, at least the AR-92 cabinet has fully square corners, but you'd still need to deal with that painted front baffle. Just an idea, but check out this terrific resto-mod project on a pair of AR-91's.

    

[npeters]

Oops. Don't try this at home....

I had the AR92 speakers in the kitchen on a benchtop, because I am convinced they are actually finished in a real wood veneer (and not vinyl) - I think they have been professionally veneered at some stage. I had some dark brown scratch cover stuff open in one hand to wipe down the veneer and give it a nice even finish ready to take some furniture oil later, and as I was rubbing the dark brown scratch cover stuff in with one hand, I inadvertently and without knowing it was happening spilled a puddle of the bloody stuff on the wooden kitchen floor. Sure works on that pretty well too...

The speaker cabinets came up beautifully, by the way. I will replace the black grille fabric as they are dusty and have a small hole, and I have decided that am not going to touch the painted brown front panels other than with some new blanket felt - a small touch-up will do for these.

60mm paper domes ordered. What glue is recommended for these? The original looks like rubber cement - will a PVA (white wood glue) do the job or do I need something more robust?

I have opened up the cabinets. The polyester wool packing inside is fine. II have freed up the frozen level switches using contact cleaner and set them to "0", and the capacitors on the crossovers look physically in perfect shape - no bulging is evident. There is a lot of hot glue in there...

Some listening to come to see what still might be needed regarding the crossovers if anything. I am beginning to suspect that these speakers have seen almost no use....