Mr. Weather

I looked through several pages of AR90 images in a duckduckgo.com image search and that was one.

I made new slim side grills for my AR90 speakers, so the original 4 side grills have been waiting to be stored. I am not a fan of the original thick side grills and I've always wondered why they're designed like they are. One of the 4 was coming apart so I decided to pry it open and see what was in there. Opening it revealed that the outer grill assembly (3/4" thick) has holes for mounting pegs that are not used. The thinner plastic frame (1/4" thick) was glued to the larger frame that holds the fabric, and the thinner frame is what attaches to the cabinet with pegs. For some reason, AR glued this plastic frame in the middle, even though the outer frame was designed to be mounted to the cabinet. I have no idea why this thinner frame was added. It just makes these side grills protrude more. Maybe that was the point, to draw attention to the side mounted woofers. The thicker outer frame and inner thin frame add up to 1+ inch. The cabinet has two of these, plus a small gap where they mount to the cabinet, which adds more than 2 inches to the width of the overall cabinet. Clearly someone in the past attmpted a sloppy repair of these and I found two other kinds of glue that was not the factory glue. The factory glue is slightly brittle and when pried with a flat screwdriver, it snaps and the parts release. The origial glue can be scraped off without too much effort. But the other 2 glues were different. One was gummy and one was a hard foam like Gorilla Glue. Anyhow, the bonds released without damaging the original plastic frames which are very study. I will finish removing the glue, wrap these up, label them, and store them somewhere safe so that they can be paired back with the cabinets in the future at some point should someone want to make them 100% original again and ditch my new side grills.

The crossover is on the back of the cabinet, inside. Typically you would remove the woofer by removing its screws, then remove some of the insulation inside the cabinet. This will reveal the crossover parts. Howver you can also remove the tweeter, disconnect the wires going from the tweeter to the inside of the cabinet, and use an ohm meter to see what the tweeter's resistance is. The same multimeter may also have a continuity tester which can be used to see if the tweeter has continuity. If the continuity doesn't happen, or the tweeter has an ohm measurement that is way out of spec or it can't be measured, then the tweeter probably needs to be replaced.

Thanks for the replies. I found some foam packing sheets that are often used between ceramic plates or dishes. Thank my wife for pointing out that we had some. Here are some photos of an original gasket compared to these foam sheets. The original is more dense in feel and look, but both are the same thickness of about 1/8". Presumably there is someone out there who could write in depth about the differences of these chemically and physically. So these aren't the same but probably a good easy to find solution. I think these would work just fine to seal the cabinet.

No luck so far in my query after a couple of days. I will order some foam sheets and compare those to the one original foam gasket and see if they're even close.

The OLA tweeters use a white foam sheet material for gaskets between the tweeters and cabinet. This doesn't seem too exotic but a quick search doesn't turn up much. Where can I find this material or these gaskets pre-cut? Amazon sells all kinds of workable materials, but presuambly someone sells some pre-cut from a material that's known to be exactly what was originally used. I am not worried about the sealing or acoustic qualities here. I'd just like to have an original or original-looking part.

They look great. Did you do any sanding or similar between or after applying the finishes?

I finiished up the second set of new side grills. I put slightly more fit and finish into these, although they're the same size and will look the same from the visible side. I will keep the original grills in safe place and attach a label to them so in a decade I know what the heck they are. The last thing I want to do on this project is haul the speakers outside again and photgraph them on a sunny day in the same place as when I got them on day 1. Between my time and the weather, I haven't been able to catch the sun yet but I'm in Houston so we're about to start our 8 month tropical summer which includes mostly sunny days.

Thanks. Yes I need to push this one back to the wall. I had been sliding it around while fitting the new grills and didn't get it quite right. Fortunately the room allows these speakers to go right up to the wall baseboard.

I made a pair of new side grills as a test that actually turned out pretty well. The primary design goals were to use the existing mounting holes and make a wooden frame as strong, slim, and compact as reasonably possible while not interfering with the operation of the woofer. I used cabinet grade pine boards left over from another project. I ripped them down to 3/8" thick and used half lap joints at the corners. The joints were glued. The real trick here is that the original mounting peg holes are not totally symmetrical: The holes near the front of the cabinet are spaced closer together than the the rear ones. The mounting locations have to be done in a mirror image for the grill on other side of the cabinet. I rounded the corners which of course does not match the aesthetic of the original grills or the cabinet design in general. The more compact size of these grills allows more of the walnut veneer to be seen and that of course exposes another difference of these which is that I did not repaint original black around the woofers. Yes, this is all perhaps blasphemy because it deviates from the original design of these. I really don't like the original side grills. To me, these new grills look more correct and far less awkward than the original bulky design.

I was able to get reproduction AR90 badges but these are just thin metal plates with no mounting hardware. That's the tricky part. Until I can find some original badges with their mounting bits, my home made parts will have to do: I cut a couple of .75 x 1.5 inch pieces from a piece of 18 gauge steel sheet, and welded a couple of large finishing nails to the plates. I cut off part of the nails and ground the ends back to dull points. I got a wine cork, cut it in half, and shaved each half down to a smaller cylinder. Then I drilled a very thin hole in each cork. Cork goes in back of speaker grill. Metal plate sticks in front. AR90 badges stick to plates. Done. Astoundingly, it all worked the first time. I waxed the walnut veneer and man, it's glassy smooth and looks amazing. I had to paint rusty the tweeter screw heads in 2 batches. That worked OK. I washed and dried the side grills. Long story short, everything is back together and they sound fantastic!

I used some Testor's model paint to cover some small imperfections on the edges and corners and that worked exceedingly well. The Danish oil seems 95% cured and the results are: 1) The color of the wood is amazing, an absolutely beautiful color that is truly walnut and not too red, not green, not yellow. The original walnut has a beautiful luster and depth now. The sheen is slightly uneven, although you have to look for it in the reflection of the lights. Some areas have a less-than-semi-gloss look, and this seems to often relate to the underlying grain. I think this may mellow out over time. I will try some wax after a few more days. The photos show the veneer repair. The repaired area at the bottom of the cabinet is highly obvious. The grain and color do do not match, perhaps because the original wood is 40 years old and the replacement is not. However the problem of chipped and peeling veneer is fixed. The factory black fronts have some uneven areas. I was able to remove or reduce the previous-owner black overpaint in all areas, and small dings in the original black paint are more hidden. The black rear sides are good, but in a harsh light reflection there is still some uneven tone to the new black paint. I failed to get a photo of the bottoms but they look great. They match and are super solid. On the tops, you can see some remnants of the black paint in some of the slight gouges in the wood surface. The positive way to look at these is they add character The next step is to reinstall the drivers and give them a listen. After that I need to get the new badges mounted on new mounting plates installed on the grills. Then maybe I'll work on some thinner side grills. We should have sunny weather this weekend and I may put together some before and after photos.

The Danish oil is moving along. I applied a 4th coat this morning and that's it. It needs to cure more and then get buffed. Maybe I will wax it, but not for several days. I measured the threads of all of the screws while I had them out, and the measurements are in a photo below. (spoiler, most are #10 with 24 threads per inch, the others are 1/4" x 20 threads) Most of the screws were showing some rust, so I brushed them with a small stainless steel brush, cleaned them with alcohol, and gave them a light coat of matte black paint on just the heads. The screws for the LMR drivers did not need paint so I left them alone. One of the woofers had one slightly undersized screw. Amazingly in my random assortment of screws, I had a few that were near perfect match: The correct threads, nearly the same head, light black in color, and only about 1/4" too long. I hand painted a number of really tiny dings and chips in the factory black paint, and I need to do the same to some edges where the light colored particle board is visible, but I will use a brown paint that matches the valnut. You can see this on top rear corner in the photo below where the light MDF stands out between the walnut top/side and black rear. I have not done much with the front grills, but today I washed them with soap and water. I am not inclined to recover them as the holes are not highly visible except one pea-size hole. The resulting wash water was filthy though: grey-brown. I was able to get new AR90 badges, but they do not have any backing plates. It should be really easy to make backing plates using a small piece of sheet steel with a small nail welded or glued to the back. Securing this in the grill mounting hole can probably be done with a small cork instead of the original metal push-on nut which is probably difficult to source cheaply and difficult to make. We shall see.

I made a great deal of progress tihs weekend. In review: 1. The rear of the cabinets posed a challenge. The bare MDF soaks up paint like a sponge, and the high porosity and varied condition of the wood means that the painted finish is uneven and splotchy, even with 3 coats of paint. Rattlecan paint is splotchy enough anyhow. Probably I should have used a primer. However, I settled on this formula: 3 coats of paint over an hour, let it dry for a couple of days, then sand with 320 grit, wipe down with alcohol, then apply a single, even final coat working as carefully as possible, and don't mess with it. I think the resulting sheen is greater than the factory paint, but it's totally acceptable. 2. The bases worked out well. One cabinet of course didn't need much work. The other one needed a new base which I replaced. Both cabinets got a 1/4" solid oak footer, kind of like a horse shoe, to protect the base panels and provide a strong attachment point for feet or whatever. In the cabinet with water damage to the MDF, I applied 2 coats of epoxy and then stuck on the new plywood base. At some point I masked the cabinets with plastic and tape (yet again), and used the same black paint on bases to match the factory paint, however I did not paint the surface of the oak that contacts the floor because there's no reason for that to be painted. 3. Veneer repair: This was challenging. The basic premise worked. I even used a piece removed from the large area of damage to repair a smaller damaged area. But the new veneer has a more contrasty look than the original so it's not a great match. I also had problems with the new veneer chipping at the lower edge even when I hand sanded it. Probably I did not use enough glue. I filled in some small areas with wood epoxy putty and those did not accept much stain and do look lighter. So, ultimately the major damage is fixed and physically tied off, but the end result is not as polished as I wanted, cosmetically. 4. I gave the factory original walnut veneer a quick once over with 320 and wiped it down with acetone and paper towels to remove any residual dust or contaminants. The weather today is perfect with a high of about 72*, mostly sunny, and low humidity. So the acetone flashed off quickly. I cracked open a new can of Danish oil and started applying it with a clean used cotton rag. All I can say is wow! Instantly the walnut looked fantastic. Really amazing. Just after staring the first application and seeing how great it looked, Hotel California came on the radio. I am not superstitious but I saw this is a a good sign because it's a great song and great album, in spite of the poor folks being condemned to Hotel California for eternity. I applied a heavy coat of Danish oil, let it soak in 15 mintues, then did a second one, let it set a while, and then wiped it down. There was not much residual to wipe off; the walnut soaked up 99.9% of the Danish oil. That was all done per the instructions on the can, and I will consider that one coat. I dollied the cabinets back inside and they're resting. (I must have wheeled these things in and out of the house a dozen times now.) After about 24 hours, I will sand them with fine sandpaper (or use steel wool), wipe clean, and then do a second coat. At a minumum I will do a 3rd coat but I don't know if a 4th will be needed. I don't want to overdo it and somehow end up with a bad result. You will see in two of the photos that the lower cabinets near the woofers have a different look to the wood. This is real, and it has always been there since I stripped them. Whatever was done at the factory originally has caused the wood around the woofers to be lighter. Clearly it relates to the fact that these were painted black at the factory in that area. This was always as risk for this project so I can accept it. I don't know if this will minize with more Danish oil, or not. There is always a possibility to re-apply the factory black pattern of paint, although that is not my preferred route right now. I will need to touch up the factory black paint on the fronts in some areas, but I will probably use a small paint brush to dab it on carefully. Anyhow, I am totally jazzed that the walnut shined up like it did. This is a great step forward. Can't wait to get these things rocking again.

I applied a second batch of epoxy and used that to attach the new base. Next major work is the walnut veneer repair after it arrives.

Advent may have made 5 million of these (wild guess) but I'm glad to have found these survivors.

Thanks! I suppose the lighter fabric color is sacreligious but they do look much better. I am still trying to find a single original tweeter (or a pair), but man, the single working speaker sounds fantastic. Looking forward to getting its companion fully functioning. Now that the project has shown some benefit, I feel lucky to have found these locally on Ebay. I paid $60, and the quality of the cabinets is fantastic. I originally was outbid on them, but the speakers were re-listed a week later and got them for $10 less than I had bid the first time. When I met the seller to do the deal, I learned he is a chronic estate sale buyer and buys spefically to sell on Ebay. So probably these were an estate sale pick.

Seems reasonable. As I've gotten old I've realized that the looks of something may fall in and out of favor over the decades. Could be the same here. Ultimately the quality of the sound is what matters most here.

My theory is that thinner side grills would be less distracting looking. But it could be true that any grill on the side would be distracting looking, and shaving 1 inch off the grills wouldn't make any real improvement. I feel compelled to at least make one and see how it looks. Good thread. Great that the OP got the AR-90's for $125 in 2010.

Does anyone have any thoughts on the side grills for the AR-90? I have always thought these looked odd and have never cared for the look. I suspect their bulky presence was designed to draw attention to the woofers on the sides of the cabinets which may have been unusual at the time. AR wanted people to notice them. Anyhow, I keep pondering the prospect of reproducing the side grills, but making them much more slim. Each grill assembly about 1-1/8" thick and protrudes about 1-1/4" from the side of the cainet. It seems like it would be possible to build one that was no more than 1/4" thick and maybe protruded only 3/8". This could be done with pine boards cut down to 1/4" thick and maybe 1-1/5" high, and joined at the corners with a glued half lap joint. Paint them black. Install mounting pegs. Staple on black fabric.

I am not surprised to hear this. Seems like a reasonable difference. It's a piece of evidence to support the idea that it is difficult to find the authoritative source of truth with sound. While people can agree on technical standards such as flat frequency responce, high dynamic range, low distortion, or perhaps replacing worn, old, or faulty electrical components, I am reminded that everything in the electrical paths can potentially make a differnece, audible or not, measureable or not. When you add in the decisions of the musician, recording engineer, music producer, or author of the recording software or designer of the studio monitor speakers, or the team who designed the home listener's audio amplifier, there are countless variables. I was reading about the history of Rudy Bozak. After years of successful work and products, he was reluctant to adopt acoustic suspension designs. The man spent a lifetime designing speaker drivers and experiementing with materials. He thought things should be a certain way and that's how he designed them. I mention that because like any endeavor, I think it's great that people can have a discussion about the finer points. While audio might seem like a straightforward science, it's far more complex than that when you go down the rabbit hole.

All of the capacitors are replaced. I got more accuate measurements of the old caps this time and some of them are still in spec. The last 40 uF broke when I took it out, so I did not measure it.

Good catch. Fortunately, as you mentioned, this was the angle of the photo. Here is an overhead shot. I did glue down the new components (and the 1 ohm resistor) to ensure no shorting. That is a fantastic schematic.

Yes those are handy. I ended up using a compact gooseneck desk light that worked well. The caps are all swapped on one speaker. The uppermost cap is a real bear. Not easy to get the soldering iron and solder up that high while trying to see into the cabinet. For some of the replacements, I ended up leaving some of the old capacitor wire in place, bending that into a tiny hook with needle nose pliers, making the same hook on the new capacitor wire, and then hooking the two together. Then the new one stays in place for soldering.

Yep, that one is on the top of the rear board and looks to be a stretch. I took one photo and couldn't even see the dang thing. However later I realized if I go in from the other side it's more visible.