AR-2ax Speakers

Last year, I was given a free pair of AR-2ax speakers. I gladly accepted them, but I knew they’d need some TLC. I also knew from previous research that these are pretty nice speakers when they’re fully working, so I figured it would be worth it to fix them. I took on the task of restoring them late this July, as part of an effort to reduce the number of unfinished projects I was holding onto.

My research has taught me that the first run of this model went from 1964 to 1970 and AR may have made as many as ~125,000 in this run. Given the low serial numbers of this pair, they were likely made in 1964, which would make them 50 years old now. This page shows some pictures and someone else’s rework of their pair.

Here’s a picture of the labels on the back of mine, showing their fairly low serial numbers:

CIMG6211 CIMG6210

If you’re trying to follow this page as a guide, see Restoring the AR-3 first. It’s far more thorough and nearly all the advice applies to the AR-2ax just as well. I’m writing this as a guide and I do have some info the AR-3 guide doesn’t cover, but their guide is still awesome. I have no interest in trying to outdo it.

Disassembly

One of the worst things about servicing a pair of these is opening them for the first time. I kid you not, their grilles are stapled on with about 12-20 staples. Each staple is nearly-impossible to remove non-destructively. Luckily, Acoustic Research learned some kind of lesson, probably from having a few of the first couple thousand sent back to them for repairs, at some point between #1570 and #2186 (the two I own), they changed the grille design to make it far easier to remove the grilles without removing every dang staple first.

Version 1 (serial number <~2000) – The grille (1 layer of masonite) is held on by staples and a lip on the enclosure. (Likely designer thoughts: “This will PREVENT EVERYONE from opening these WITHOUT DESTROYING THEM. MHAHAHAHAHAHA!!!!”):

AR2ax Grill Style 1 CIMG6230

Version 2 (~2000 < serial number < ? – The grille (2 layers of masonite) is held on by staples only (Likely designer thoughts: “This will discourage our customers from opening these, but, just MAYBE, WE will be able to without destroying them if we need to service them.”):

AR2ax Grill Style 2 CIMG6229

Side-by-side shot:

CIMG6217

No joke, the best advice I can give about removing the grilles is to source some good replacement grille cloth before trying – that way you don’t need to be careful at all with the old ones. Unless they’ve been cared for impeccably and kept in the dark, your speakers will look way better if the grilles are replaced. If you’re lucky enough to find matching cloth (loose-weave natural slubby linen with ~22.5 threads per inch), you’re golden. If not, at least you’ll know you need to be VERY careful when you remove the staples.

If replacing the grilles

You can be a little destructive with the cloth, masonite, and staples. Find something to pry them with and then tap it underneath them gently with a hammer. After it’s under them, you should be able to pry them out easily.  Grab them with pliers and yank them out after they’re raised enough. If you have version 2 grilles, you’ll be able to lift up a corner after you’ve removed a few staples. Then you can pry the rest of the grille up from underneath. If you have version 1 grilles, sorry, you’ll probably still need to remove every staple to safely lift out the grille.

If not replacing the grilles

Remove the staples very carefully. The best tool I had available for prying at them was one tip of a pair of scissors. You’ll also want to have a flat screwdriver and a pair of pliers available. Try to work the tip of your prying instrument under the staple head and then pry upward. Try using another tool as a fulcrum to give yourself leverage. When you’ve worked the head of a staple out far enough, you should be able to grab it with pliers and yank it out. Be VERY careful not to break a staple – this could make removing the grille very difficult, especially if you have version 1 grilles.

Removing the woofers

You’ll need to remove the woofers before you can check the internal components of the speaker.  The procedure I used was to remove all screws, cut away as much of the sealant putty as possible with a utility knife, then pry at the edge with a paint can opener (credit: Restoring the AR-3 – a great resource).

A lot of people throw the old putty away and replace it with something else. I saved the putty from mine and reused it. The putty still seemed fine and it just seemed a lot easier to reuse it instead of shopping for a substitute.

Fiberglass Batting

Do the work of removing the batting outdoors. Use gloves and a face mask. I saved the original batting and reused it, but replacing it with rock wool or denser fiberglass is a fine alternative. (Rock wool is less itchy, too.) I put the batting from each speaker in its own kitchen garbage bag and placed the rotten fabric stuff from behind the woofer on top so I’d know where to find it later. Leave the bags somewhere they won’t be disturbed until the batting is ready to be reinstalled. Remember what they are, so you don’t accidentally throw them out with the garbage.

Crossovers

The crossovers in these speakers are dead simple. They’re nothing more than simple high-pass filters for the midrange driver and tweeter. A rheostat for each driver functions as a level control. It also has a weird custom capacitor pack, with 4µF and 6µF both in the same wax-filled paper box. I believe it uses wax paper as a dielectric, but I could be wrong.

Rheostats

Unfortunately, the copper wipers in the rheostats AR chose for these speakers are highly prone to galvanic corrosion because of the bimetallic junction formed by the wiper and winding.

Taken apart and cleaned up a little, here’s what they look like:

Pots - breakdown Pots - dead wipers

I tried cleaning mine, but it was futile. In the second pic, you can see that the wiper on the right appears to be mostly fine. However, the contact portion of it is corroded all the way through. No reasonable thing can be done to save it because of this – it’s simply broken. The only thing to do would be to make a new wiper from a different metal with the same anodic index as the winding. Personally, I’m not interested in doing that.

Some people like to use Ohmite RHS15R or RHS15RS rheostats as a replacement for the original defective part. This is what I did. It’s a more expensive option than using an L-pad, but it stays more true to how the original controls functioned. I considered building a housing that would allow the new Ohmite rheostat to use the original rheostat’s knob, but ultimately decided it would be too much trouble. Instead, I bought Ohmite knobs to install with them. I’m happy with my decision, because they look pretty nice – I think better than the original knobs:

knobs

The picture may not make it obvious, but the new knobs do have enough room to turn without scraping against anything.

From the inside, here’s what the new rheostats look like installed:

RHS15R protected RHS15R installed

Note that I used heat shrink tubing to protect the solder joints and that I’ve used zip ties to bundle the cables. I don’t know that this is actually necessary to do, but I don’t like leaving large open loops of wire or exposed live metal for no good reason.

It’s also best to protect the open-backed rheostats with a housing, so the wiper doesn’t get clogged with fiberglass. I opted to use old cans from a popular beverage for this purpose, whereas others may prefer to make a wooden box that partially covers them. DO NOT enclose them completely, especially with wood or something else insulative that’s also flammable. They WILL get hot.

Capacitor Pack

When I tested the original capacitor packs, they all tested at almost exactly 325% of rated capacitance. This may seem like a sign that “they don’t make them like they used to”, but the truth is that this is way too high to be explained by a factor of safety for a part used in this setting. Some old capacitors are made with hygroscopic (water attracting) dielectrics and are wax potted to stave off the absorption of water from the air over time.

Given how so many modern capacitors (electrolytics in particular) fail by loss of their capacitance, it may seem counterintuitive that a capacitor’s failure mode could involve its capacitance increasing. But the reason for this is simple – the absorbed water increases the dielectric constant of the dielectric (and therefore capacitance), but also makes the dielectric more conductive, ruining its voltage rating and increasing its leakage current. So a capacitance that’s way too high means this kind of capacitor is ruined. In a crossover, this has the potential to overload your drivers and burn them out – so they really need to be replaced.

Wax paper or paper-in-oil (PIO) capacitors can be great in audio applications, but ONLY if they’re hermetically sealed. Unfortunately, these were not and exposure to the atmosphere over time ruins them, no matter how much or how little they’re used. Film capacitors are a good low-cost alternative; you can simply form 2µF caps into a pack by gluing them together (e.g, with hot melt). I believe the capacitors I chose were made by Kemet and cost about $1-$2 each. You can see the packs I built toward the left in my pictures of the new rheostats:

RHS15R installed

If you’d rather have a something more similar in sound to the original capacitors, search for surplus PIO capacitors from the old USSR. Get the hermetically sealed cans. These are especially good if you enjoy the irony of using cold-war-era Russian parts in cold-war-era Americana. (Bonus points for using mil-spec parts.) There are still plenty to be found on eBay and they’re reasonably economical if you buy 10+ at once – some sellers will even lower their base price if they’re selling in bulk and you also save on combined shipping this way too. Be prepared to wait a while for them though.

So you know what to look for, here’s a pair (out of 12) I bought from Bulgaria a while back:

USSR Caps

Mid/Tweeter

With the crossovers working again, the mid-range driver and tweeter will hopefully also work. Test them to be sure. Connect the speaker (sans woofer) to an amplifier and test assorted frequencies with a tone generator. A logarithmic sweep will also work very well. They won’t sound great for music right now,  due to a lack of bass response, but you should hear a continuous response that extends to the upper end of your hearing and doesn’t crackle. This will tell you that mid-range drivers and tweeters are working properly. If you can verify this way that they work, you never need to remove them from the cabinet, which is really nice given how they dedicated they are to staying mounted in it and how much trouble it is to re-mount them.

AR2ax - mid and tweeter

If one or more of them isn’t working when you test it, check your crossover wiring and components first before pulling it. If it really isn’t working, sorry, you’ll either need to repair or replace it. If I were in your position, I’d probably try to buy a working pull before anything else. There are likely also good repair services for these, but I wouldn’t be able to recommend one. My experience with other brands tells me that you’ll probably spend more having these repaired than simply replacing them with a working used one, so I’d recommend trying very hard to find a used original replacement first.

Assuming the tweeter and mid-range driver are both working, you can now put the fiberglass back in the enclosure. Try to arrange everything more or less how it was when you pulled it all out – make sure the woofer lead wires are accessible and arrange that delicate paper stuff roughly how it was before. If you have it all placed well enough, there will be plenty of room for the woofer without it making direct contact with any of the fill material.

Woofers

If your woofers are anything like mine were, they’re probably falling apart. Unfortunately, the adhesive AR used to attach the spider and surround gaskets to the basket isn’t actually very good for attaching masonite to aluminum once it fully dries, which is unfortunate since that’s what these parts are made of.

This is what you’re likely to find when you inspect them:

woofer oops 1 woofer oops 2

They peeled off almost effortlessly. Sad. If yours do this, make sure you mark them inconspicuously before peeling them all the way off so you know how they’re supposed to align. I didn’t do that, so I had to guess. Also, you’ll need to use a soldering iron to disconnect the voice coil leads while you work on cleaning surfaces up for re-gluing – don’t just snip them.

Not all is lost though. The gaskets can be glued back to the baskets. First though, you should test to make sure your voice coils are still good:

voice coil test 1 voice coil test 2

Beautiful, mine were still good! If you read something in the neighborhood of 5-7 Ohms, they’re probably fine. If not, you’ll need to shop around for woofer repair or replacement too.

Now that we’ve verified that the voice coils are still good, make sure they’re still glued on tight. The glue on mine looked a bit rough, but was still holding. I left it alone; I figured if it held for 45 years already, I should trust it to hold on for a while longer.

The gaskets and baskets will need to be thoroughly sanded and cleaned with solvent. Before you start, cover the voice coil’s little home with tape. I recommend using acetone as a solvent to clean the aluminum, as it should do a slightly better job than rubbing alcohol at carrying away the old adhesive. But don’t get any of it elsewhere, like on the cloth surrounds. It can potentially damage or destroy the glue bond that holds parts together.

CIMG6192 CIMG6195 CIMG6197 CIMG6191

Blow each piece off with compressed air between sanding and using solvent, taking great care not to damage the cone, spider, etc. in the process. After you’re finished using solvent on the glue-bond surfaces, remove the protective tape and blow the voice coil’s little home out with compressed air too. It’s likely there will be some grit in there. I recommend also cleaning the voice coil one last time very gently with a cotton swab and some rubbing alcohol, so there isn’t any grit lingering on it.

I used Simply Speakers Repair Adhesive to glue the gaskets back onto the baskets. I expect that to work a lot better than the original adhesive did, but other similar adhesives should work acceptably well. Unfortunately, I didn’t get pictures of this part of the process – but that’s spilled milk now.

I learned to install new surrounds on speakers from this video. Other videos on the same channel may be helpful before you start this process.

My procedure was as follows:

  1. Glue the spider gasket in place.
    1. Apply a bead of adhesive around the middle of the bond surface of the basket.
    2. Carefully lower the cone assembly and voice coil into the basket. Be sure to align the voice coil carefully. Make sure the cone assembly is rotated correctly relative to the basket before letting the gasket make contact with the adhesive.
    3. Gently squeeze the gasket and basket together to spread the glue.
    4. Without attempting to restrict the movement of the surround gasket in any way, gently press the dust cap straight down at various points. (it may help to use something like a capped pen for this.) If you can hear the voice coil rub, it’s rubbing worst on the opposite side from where you’re pressing it. If this happens, imagine an arrow pointing from the center of the dust cap to where you pushed it to get the most rub and move the gasket in that direction. Very small movements are best. Your objective is to reach a state where the non-rub zone is centered as well on the dust cap as possible. If you do a good job on the AR-2ax, you can push on nearly any part of the dust cap without the coil rubbing against anything. Work quickly and carefully – if the glue gets too tacky, it’ll become hard to work, but if you rub the voice coil too much, you’ll ruin it.
    5. Let the new glue bond cure for an hour or two. Check a couple times early on to be sure the gasket hasn’t drifted. If it has, correct it as necessary.
  2. Glue the surround gasket in place.
    1. Try shifting the surround gasket around a little. Note that some placements of the gasket leave the surround in a more natural-looking state. In some positions, it will take on a more-or-less uniform shape all the way around.
    2. Apply a bead of adhesive between the surround gasket and the basket.
    3. Gently squeeze the gasket and rim of the basket together to spread the glue.
    4. Try to position the gasket so the surround looks as uniform as possible all the way around.
    5. Just like in the previous step, gently press the dust cap at various points. If you can hear the voice coil rub, it will generally be rubbing worst on the opposite side from where you’re pressing it. If this happens, imagine an arrow pointing from the center of the dust cap to where you pushed it to get the most rub and move the surround gasket in that direction. Very small movements are best. Your objective is to reach a state where the non-rub zone is centered as well on the dust cap as possible. If you do a good job, you can push on nearly any part of the dust cap without the coil rubbing against anything. As before, work quickly and carefully.
    6. For the first 20 minutes of drying time, occasionally check to make sure the gaskets haven’t drifted. If they have, correct for the drift.
  3. Let the woofer cure for about a day, resting on a level surface.
  4. Test the voice coil resistance again with a multimeter. If it still reads somewhere close to 5-7 Ohms, it’s still good.
  5. Solder the voice coil leads back in place.

My procedure requires a delicate and agile hand, but does not require shimming the voice coil or removing the dust cap. I believe alignment can turn out better than what you’d get with most procedures that involve shimming. But it does carry a higher risk of damaging a voice coil, especially if you’re not careful. Decide for yourself what technique you’d rather use.

Once the woofer is fixed, you’ll need to use skills you hopefully developed as a child – knead the sealant putty until its hardness is somewhat uniform, then roll it in your hands to create long pieces of it. Join the pieces together and lay them out around the woofer hole on the enclosure, where the putty was before. I recommend running your roll of putty toward the inside of the screw holes for a good air seal. You’ll likely have some putty left over – I think that’s fine, as there was probably too much to begin with. I had a fair amount left when I was done.

Once the putty is all in place, reconnect the woofer’s lead wires and gently position the woofer on the putty, lined up with the screw holes as well as possible. Set each screw very loosely before attempting to get any of them tight, so the woofer can be shifted as necessary. Once the screws are all in loosely, tighten them up. Do this by tightening each one a little and then visiting another screw. This will prevent you from creating any kind of alignment error while you work. Try to get them pretty tight, but if your speakers are anything like mine were, you don’t need to get them as tight as they were from the factory. The dunglehead who tightened mine back in 1964 did a fair bit of stripping the heads before he decided the job was done.

If you’ve reached this point, it’s time to hook them up and play something. They may need some breaking in before they’ll sound their best, but they should basically play as intended now. I was told playing pink noise on them for the first few hours is a good way to break them in, so I played recordings of waves on a beach and took a nap to it; it was great.

Grilles

First, let’s just assume you’re replacing the grilles. I instructed you to source new grille cloth. If you shop around long enough, you can find new old stock that a seller doesn’t know matches these speakers. I found just that and got the stuff for about $10/yd, just one yard of which was enough to do 4 speakers. If you don’t want to shop around, there are sellers online who will happily sell you half a yard for $40-$60. Or, you can just buy replica grilles – those typically go for around $90-$100 per set.

This is the stuff I used, next to an original grille for comparison:

new grille cloth

Additionally, you’ll need the following:

  • One 2’x4′ sheet of 1/8″ (3mm) masonite/hardboard (alternately, one 2’x2′ sheet of 1/4″)
  • Matte black spraypaint
  • some high-quality Velcro – the industrial stuff is arguably justified in this application.
  • Access to a good pneumatic staple gun and an air compressor to drive it
  • Matching staples that are no more than 1/4″ (6mm) long.
  • Access to a jig saw
  • Access to a circular saw, table saw, or cabinet saw
  • Access to a drill (a drill press would be best, but a dremel or hand drill will also do)

This is the staple gun and the box of staples I used:

stapler staples

I initially tried using a non-powered upholstery stapler, which worked fine for me on materials like plywood. It wasn’t strong enough to push the staples into masonite. The stuff was just too dense for it. But the pneumatic one rarely failed to drive them all the way in. It’s possible an electric stapler would work too, but I can’t say from experience.

Assuming you have at least one AR-2ax that has the new grille style, use its grille as a pattern to mark your masonite for cutting. If you’re unlucky enough to have only the old grille style, you’ll need to guess. The hole pattern will be the same, but the long dimension of the grille will need to be shortened. And maybe the short dimension a little too. It’s fine to err on the side of caution and shorten it later based on the outcome of test fitting one. Whichever grille style you have, test fit each piece after you cut it to make sure it’ll fit – be mindful of the fact that you’ll need to allow enough clearance for a layer of cloth on each side.

I found it easiest to cut the rectangular shape of the grille first on a table saw, then mark the holes. If you’re using a 2’x4′ sheet of masonite like I suggested, you’ll have just about enough left to make 4 paint stirrers. I had none left on the 4′ dimension – I had to trim the remaining 1/16″ off the last grille with the saw. If you’re using a really wide saw blade, you might not even have enough. Be mindful of that.

I also found it easiest to staple the 2 layers of masonite for each grille together before cutting driver holes. The saw can be moved faster on one layer at a time, but that actually makes it harder to control the cut and the speed increase isn’t fast enough to make the overall job shorter.

When cutting the holes out with a jigsaw, you don’t have to be exact, but try to stay true to the basic shape of the original hole pattern. If you deviate from your lines for a moment, correct your path as soon as you can instead of trying to follow that new curve. If the edges of your holes are a little rough, try not to worry about it. It’ll be really hard to see rough edges once the grille cloth is on.

Once the new grilles are completely cut out, mark the mounting hole for the AR logo and drill it out. Test to make sure the logo goes in straight. If getting it in straight isn’t so easy, you can countersink the hole a little with a slightly bigger bit – just don’t go all the way through with it. If your logos were made using a brass screw soldered to a brass plate like mine were, it’s probably best to countersink a little for the screw head anyway.

Next, paint the outward-facing surface of the new masonite grille with matte black paint and wait about a day for it to fully cure.

Once the black paint has cured, it’s time to stretch your new fabric over your new grilles and staple it in place. You’ll be aiming for a finished product that looks like this from the back:

AR2ax Grill Style 2

Before putting the new cloth on your grilles, cut a piece for each one that’s a little bigger than the grille. Try to allow about an inch along each edge for mounting. I found it easiest to start by stapling one narrow side at a corner, stretching the cloth at the opposite corner of that side, and then stapling it as well. Make sure the grain of the fabric stays lined up well with the edge of the grille as you work – your result won’t look as good if it isn’t straight. After you have both corners of one edge stapled, keep dividing the unstapled parts of the edge with staples until you have a staple roughly every 1/2″ to 3/4″ (12mm-18mm) along the edge. So you’d staple in the center of the edge, then at roughly 1/4 and 3/4 of the way across the edge, and so on.

Once the first edge is done, do the opposite edge the same way, then the long sides. Once again, make sure you’re keeping the grain of the fabric lined up well with the edge of the grill as you go. Once the grille cloth is all on, screw your AR logo onto the new grille.

Once the grilles are finished, I recommend installing Velcro on 6 points of the back of each grille to hold them on. Use the same pattern so the grilles are interchangeable. I recommend stapling the Velcro at the edge to secure it once it’s placed, mostly because the back surface of the masonite will delaminate if you tug very hard at the Velcro.

If you use industrial Velcro, the grilles will be held on very tightly. Hopefully, this is what your finished product looks like once the grilles are installed:

AR-2ax Restored 1 AR-2ax Restored 2

Unfortunately, the lighting is a little yellow in these pictures, but you can still see from the comparison with the old grilles that they look way better now.

One thought on “AR-2ax Speakers

  1. ya

    Well done. That was a lot of work there. They do sound pretty good. They have the best bass response of all similar size bookshelf speakers that I have own.

    Reply

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