AR90 Woofer Repair - Recommendations Needed

[briodo]

I recently picked up a pair of AR90's from Craigslist in fairly rough condition. The price of $100 was right, but one speaker appears to have been dropped with enough force to crack the base of the cabinet. Both will eventually need refresh on the walnut finish, foam surrounds, and capacitors.

The one speaker that was dropped has a woofer with a tear in the paper cone. I've attached pictures to solicit ideas on how to best restore it. While I could glue it with some high strength epoxy, I really can't tell if there is coil rubbing or spider damage leading to a driver not functioning to spec. Since these are speakers worth restoring, I would prefer to have the driver repaired correctly. The driver still functions electrically.

While I've done several successful foam surrounds, I am not comfortable with cone repair.

Would appreciate recommendations on how best to proceed.

Thanks,

Brian

[DavidR]

Roy C is an expert on these. I'm guessing he'll recommend a cone replacement - but that's just my guess.

Great speakers BTW.

Enjoy!

[ra.ra]

Hi briodo,

For AR-90's, that price was more-than-right - - - that is simply a great buy. Very sorry to hear/see about the cone damage, but I am going to recommend you make an attempt at fixing that driver yourself before considering more draconian measures. I have no personal experience with the 031 driver, but I have completed two successful repairs on AR drivers with similar cone material. Your cone tear appears to be more lengthy than either of mine, but I will pass along the tip that was offered to me from Millersound.

Use a white Brawny, Costco or any coarse paper towel, about a half-inch beyond the damage. Do not wet it or thin the glue, as that particular cone will warp. Apply from behind, and work it with fingers on both sides of cone. Do it quickly before glue gets tacky and thereby creating the problem of your fingers pulling the paper (and cone) apart. If you work it too much, it will also stretch the cone material.

This basic technique works very well if you are just welding two sides of an irregular tear. In my case(s), I substituted brown coffee filter paper for the paper towel recommendation, but either of these paper types has sufficient multi-directional fiber strength to form a bridge across the unfortunate rip. Use a simple white glue like Elmer's, and while there may be temptation to thin the glue, Bill's advice hear is very sound - - - too much moisture may warp the cone paper.

edit: looks like you've got one of those double dust cap situations - - - I've never understood the purpose of the outer cap on these drivers.

[JKent]

Great tip, RA but there's a lot of damage there. The cone is pretty shot and of course the foam surrounds have to be replaced. And who knows if there was any other damage from the drop.

Those speakers are well worth having the repairs done right.

IMHO your best bet is to have a pro repair BOTH woofers. Try sending Roy a PM and see if he'd be willing to repair them (he does that kind of work for "Vintage AR").

Or just pack up both woofers and send them to Bill LeGall at Millersound. Bill's an absolute wizard. He did a beautiful job on my AR-91 woofers.

Good luck.

-Kent

[briodo]

Thanks for all of the feedback. I will contact Roy to learn more about repair options. My concern is whatever caused the tear torqued the voice coil and that damage is something I will not see. It might lead to problems down the road.

My research found the 2000031 driver was only used on the 90 which I assume means there are very few replacement drivers out there. Repairing the original should be worth the effort.

It looks like my initial damage assessment being from dropping is not correct. Further pictures below show what appears to be water damage causing the joints to expand from wood swelling.

The entire perimeter of the base has the joint seam expansion.

[ra.ra]

Fully agree that the length of the tear is substantial, but it looks to me like the rip is clean and the two sides just might melt back together just fine with some deftly applied TLC. Can't comment on potential invisible damage resulting from the drop, but the re-foam (with shims!) should be standard operating procedure, and that flat dust cap should be salvaged and re-used.

My point of reference with repairs is that I always first try to find a DIY solution, and I can also be a cheap SOB to boot. With this hobby, I enjoy the "finding" and the "fixing" as much as the "owning", and I'm often willing to accept less-than-perfect, so my comments are coming from that angle. With paired speaker stereo, I like to have left/right matchy-match as much as the next obsessive collector, but I'd need to have a compelling argument in order to convince me to send a perfectly "good" driver to the surgical table for a questionable transplant.

Nonetheless, if my patient indeed did require surgery, I, too, would also trust either Bill or Roy with holding the scalpel.

[JKent]

I certainly can appreciate the satisfaction that comes from fixing it yourself. And I don't know what Brian's skill level is. I'm just saying if they were my speakers I would not have the self-confidence to repair that woofer.

As for sending a perfectly good driver to the surgical table, I'd consult the surgeon first. As described in this thread http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7521#entry96067 when I needed surgery on a fairly rare Cizek woofer I contacted Bill LeGall. He said he could repair one to factory spec or I could send both for "improvements." Coming from anyone other than Bill I'd view that "improved" claim with a jaundiced eye. But Bill reconed both speakers. He wrote "I set the coil-to-pole-piece height differently than the factory did. The spider is slightly more compliant and the cone material is the best sounding I know of, for this speaker. (It has the perfect balance between stiffness, while retaining the non-aggressive sound of paper.)"

The speakers sound wonderful so I'm guessing the improvement was for real. And the cost was very reasonable. Maybe for the AR-90 it would only be necessary to recone one woofer but as I said, I'd ask the "surgeon" first.

-Kent

[RoyC]

Replacing the cone would result in response differences compared to the other original woofers. No modern replacement parts are the same as original. I would only recommend this if it were extremely difficult to find a satisfactory used replacement woofer from the era.

Fortunately, the square ceramic magnet 10 inch AR woofer was used for many years, and there are a number of 70's and early 80's iterations available which will work fine in Brian's 90's. Measurements are showing the differences between them are mostly cosmetic (ie added dustcaps)...and any differences that may exist would be much less than those posed by new cones and associated voice coils. Large cloth dust caps are still available, and much easier to install than a new cone.

Repairing the cone per ra.ra's suggestion is certainly worth trying...though the damage looks pretty nasty from here.

Roy

[ar_pro]

I've seen similar damage to AR-9 cabinets that had been left out in the weather.

It does appear that the panels are separating, and this could be much more trouble than issues with a single woofer.

[Anthropologo]

I agree the cabinets represent the primary issue as your drivers and attendant sound will only be as good as the structure they inhabit

Were it me i would remove any deteriorated/deteriorating and/or questionable mdf, clean out all separating seams and through judicious use of strong epoxy (i have had good luck with auto body filler) and ratcheting straps reseal, bring everything back into alignment, and refinish as necessary

Following that its just a matter of sourcing the appropriate replacement components......

[ra.ra]

The cabinet damage is indeed unfortunate, but really not all that bad if you possess some ability to attempt the necessary repairs, which seem to follow the typical clean-fill-clamp-squeeze-sand-paint format. Appears that the damage is limited to the painted portions of the cabinet, so fortunately these areas can be freshened up with a couple coats of new paint and hopefully you won't have any fussy veneer repairs.

Kent, I remember your fine restoration of those solid cabinet Cizeks, and with such a rare (and small) speaker model, I'd probably be tempted to call in the experts as well. Also, many of us appreciate your extensive assistance with value-based budget crossover component recommendations, so there is certainly no implication of "gilding the lilly" going on here. My point was only to caution against going down that $lippery $lope of costly restoration in search of perfection. This pair of speakers has four woofers - - not two - - so the question I was challenging is, "Just how far does one go?"

I read Brian's comment that the 031 woofer was only used in this particular model, and at the same time I was wondering if there might be suitable replacement alternatives. Roy's response seems to suggest this is indeed a viable option, so it might be helpful to identify a few speaker models which might be able to sacrifice a reasonable facsimile. What comes to my mind first is the woofer from the later AR-2ax or the AR-5 or AR-8, or maybe even the slightly more recent 10" woofer from the AR-12?

[DavidR]

I believe the AR90 woofer is an 8 ohm driver and with the two wired in a parallel you would get a 4 ohm circuit. The other woofers, to the best of my knowledge (which by no means is as good as most of the members here), are 4 ohm.

[briodo]

This has been incredibly helpful. My plan of action is to try a 10" replacement from a pair of AR 14's I picked up this summer that need refoaming. They are simply lower on the refurb list than the AR90's.

I did pull a AR14 and an AR92 10" to do a quick DC coil resistance check. The 90 and 14 both come in around 6.0 on my Fluke DVM. The AR92 comes in at 3.4. Now I will qualify that I have not listened to the AR92 for some time, was holding onto it for spare drivers. The 92 driver appears to be a different design than the 14 and 90. I tried to capture part numbers with resistance measurements.

200004-2 = AR14, 1978 datecode

200031 = AR90, 1979

200033 = AR92, 1980

Great insight on the damaged cabinet being the biggest challenge. I like Ra's point on clean-fill-clamp-squeeze-sand-paint, which is within my comfort range. The damage does not come near the walnut veneer, so this really becomes a structural integrity effort and let a nice coat of paint hide any rework.

Thank you again for taking time to share your knowledge. Will share more pictures as progress is made.

[rrcrain]

Check out a woodworking shop for a joint repair kit. If your lucky, you can find a kit with white glue in a hypodermic needle ideal for injecting glue deep intp the cracks.

Due to the condition of the cones, do check the resistance between the speaker frame and terminals. Either terminal will do. Use the highest ohm range on your DMM and make absolutely sure the meter indicates an open (OL). Anything else and you risk blowing out your amp.

[briodo]

An update now that the AR90's made it to the top of the repair queue. I decided to take the DIY approach based on wonderful insights shared earlier in the thread. The two biggest challenges were the torn 10" woofer and the water damaged base of one of the speakers.

I've attached some before and after pictures to show repair in progress. System is close to finish, but still needs repaint and oil finish along with fabrication and screen material for the four replacement woofer grills. I like the way they are coming out however.

The 10" woofer repair went very well. Used a coffee filter as suggested and some clear fabric glue for the patch. Before and after are below. I had to refoam 8 drivers total as I had a pair of AR14's to complete as well. I then used the AR14's to do L/R comparison of music material while rotating the 10" drivers through on of the AR14's and I could not tell the difference between any of the drivers.

Granted, my hearing is not what it was, but the bass notes all had the authority I expected. BTW, the AR14 is a wonderful speaker. First time I have heard them but was impressed how full body the sound is.

Next post covers the water damaged base...

[briodo]

The water damaged base repair was completed as ra.ra had suggested, wood glue and clamping. I ended up using bondo body filler for the large gaps as I knew all bottom sides of the AR90 are painted black. Amazingly there is walnut veneer under that paint on the sides, but I will finish it in black which will hide any imperfections in the finish. The bondo is pretty tough and will give it enough surface protection required for the average living room. Attached shows where I am now, with one speaker pretty much ready for paint and oil finish, the other will be done this weekend.

BTW, I did play them after sucking the domes out, refoam of the drivers, and new capacitors in the crossover. They sound really nice, although need to be moved into the house for a real test. Not being against a wall limits the bass and creates odd sweet spots.

The reason I stripped the black paint off is an earlier attempt by earlier owner to put some type of finish on the walnut was allowed to drip over the paint. The last picture below shows the drips in the black surrounding the right speaker 10" driver. I started cleaning it and realized removing those drips were going to effect the paint. Acetone and lacquer thinner did the work along with getting the walnut surface clean as well.

Will post more as the project continues.

Brian

[JKent]

Fully agree that the length of the tear is substantial, but it looks to me like the rip is clean and the two sides just might melt back together just fine with some deftly applied TLC. Can't comment on potential invisible damage resulting from the drop, but the re-foam (with shims!) should be standard operating procedure, and that flat dust cap should be salvaged and re-used.

My point of reference with repairs is that I always first try to find a DIY solution, and I can also be a cheap SOB to boot. With this hobby, I enjoy the "finding" and the "fixing" as much as the "owning", and I'm often willing to accept less-than-perfect, so my comments are coming from that angle. With paired speaker stereo, I like to have left/right matchy-match as much as the next obsessive collector, but I'd need to have a compelling argument in order to convince me to send a perfectly "good" driver to the surgical table for a questionable transplant.

Nonetheless, if my patient indeed did require surgery, I, too, would also trust either Bill or Roy with holding the scalpel.

Well, Brian, you proved ra.ra to be correct on these. Congratulations! I agree there is much satisfaction (and bragging rights!) from doing it yourself and you've done a great job with a woofer many of us would have written off.

One note for future projects: The white glue that comes with the foam surrounds is essentially identical to Aleene's Tacky Glue and that is what I have used for cone tears. You can also thin the glue (either speaker foam adhesive or Aleene's) with water to the consistency of skim milk and paint the cones.

I've never used Bondo but may give it a try on some future project. I have a KLH Model 82 radio that most of the veneer was missing from the cabinet. The Bondo may be just the thing to create a smooth surface for painting or applying a pebble texture coating.

Post #7 here shows a "painted" driver and Post #18 shows an Advent radio with the pebble finish. http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=8443

Keep the pictures coming!

-Kent

[briodo]

I hope someone who owns a pair of AR90's with the original grill screens can help with correct depth measurement for the bass driver grills. My AR9 grills will fit the AR90 but extend beyond the front by roughly 3/4". Is that how the original AR90 screens are or were they designed to appear like the AR9 grills and be flush with front of speaker?

AR9 depth is 15", AR90 is roughly 14 1/4".

I need to fabricate 4 new grills for the current project, want to make sure measurements are correct.

Pictures show grill on AR9 and the same grill on AR90.

Thanks in advance!

[ra.ra]

Attached is a great pic of the AR-90's, which, along with your stated dimensions about the difference in cabinet depths, should be all you need to answer your question. Definitely flush with front for both models.

Terrific job rescuing these damaged speakers. Happy to see that the cabs came back to life and that you were able to save that torn woofer cone. Nice work.

[briodo]

that's the shot I needed. From that picture, It appears both AR9 and 90 use the same size side panels, perhaps with slightly different cosmetic treatments. Since the 9 is a deeper speaker, the side grills line up flush with the wood front, roughly 3/4" back from where the front grill extends to. Looking at the first picture in post 18, you can compare with the great shot of the AR90s in 19.

While the appearance between the two speakers is slightly different, AR made them both look seamless, with clean lines and angles masking the transition. I tried to find a grill drawing in Ken's drawing collection, but could only find reference to the cabinet construction, materials, and dimensions.

Thanks for the post, ra.ra.

[Rlowe]

Attached is a pdf with 2 picture of an AR90 side cover and its dimensions.

The first shows the two components of the cover.

The second shows the dimensions I measured on a pencil "pressing".

The two plastic parts of the grille have separated (they appear to have been glued together).

The two parts are rebated into each other providing a secure location mechanism.

There are 4 screws holding them together (screws placed near screw holes in pic).

Hope this helps

AR90 side cover dimensions.pdf

[briodo]

Thank you for the dimensions from your AR90.  It does confirm the dimensions for the AR9 and AR90 side covers are the same, although there are minor cosmetic differences.  The speakers had the two front grills when I purchased them but need 4 new side covers.  I'm going to try matching your dimensions using 3/4" plywood topped with black paint and some fresh grill cloth.  The front grills need all new cloth as well.

Update on the water damage repair with pictures below.  I'm pleased with results although they will never be rated as pristine versions of the AR90.  With several deep gouges in the walnut finish, the repaired water damage bottom, 10" woofer with a repaired tear, and 4 home made grill covers. they might better represent "industrial chic".  Oh, and the 2 sucked out, but still dimpled UMR drivers... The prior owner was pretty hard on them.

So have a before and after shot of the repaired base looking at the rear bottom in both shots.  The repaired one is on the right in the second picture.  

Last picture shows the initial stain bringing the wood back to life.

Again, thank you for all the advice, this has been a lot of fun.

[ra.ra]

Excellent project. Love that hypodermic needle full of Titebond glue. Lots of passionate clever minds keeping these speakers alive.