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The good news is that all eight of those tweeters look to be in excellent condition, but those woofers do not appear to be AR originals (for the MST or any other model). The most obvious tell-tale feature is the glossy black cone, but something also looks very suspect about those wide edged surrounds as well as the screw placements. There may have been MST's outfitted with slight variations in the woofer, but they all had paper cones, normally had flat dust caps, and used only four screws for attachment.

Please post an update after you've received them, and do include some pics of the woofer removed from cabinet as well as the crossover and cabinet backs.

post-112624-0-87646500-1435590146_thumb. post-112624-0-84546000-1435590179_thumb.

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I've seen MSTs with more than four screws. The cone is another matter, unless it's a paper cone that someone has coated with something shiny. Either way, I think I'd be looking for replacement woofers. Or, if they are mutilated originals, someone who can do a complete recone.

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I don't think a recone will give you the original sound as I think all the new cones are much stiffer than the originals. RoyC would be up on this. I'm guessing these originally had ceramic magnet woofers with composite cones and flat caps as Robert mentioned and shown here: http://www.classicspeakerpages.net/IP.Board/uploads/post-101112-1171890277.jpg

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Well at least we all agree that the woofer cones look suspicious. I had had the same idea as genek that maybe someone slathered on an ill-advised coating of sorts, and since I've never entered the surgical world of re-coning, I can be of no further help on that topic.

I'd be very curious to see an 8" woofer in an AR speaker with more than four screws used for attachment, but as the attached pic attests, many non-proprietary metal baskets had punched holes with the provision for eight screws. Similar 8" woofs for Rectilinear (Mini-III) used only four screws, but my pair of early EPI-100's with butyl surrounds does use eight screws for woofer attachment - - but alas, no T-nuts.

Just for reference, attached is this pic of four different 8" AR woofers, all of which have been re-foamed within the last year or two. All have paper cones and all baskets measure 8-1/4" O.D. In all cases, the dimension from the outer edge of the foam roll to the center of the screw hole is about 3/8". The lower left is the only one with a replacement dust cap and I'm pretty sure it has a different foam as well. The lower right woofer, originally from an AR-7, is what I am using in my orphan MST project. Speaking of AR-7, the woofer shown in the second pic of post #2 looks like what I have in my AR-7's and I believe it is the Tonegen replacement part.


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I will definitely post more pictures when I get them.

One other woofer with shiny cones are the one on the ARUK1 ( AR94?)

But you are right, they still look different.

All will be revealed when I get them and open them up.



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You are correct about the shiny cones - - pic attached shows AR-94s with woofers similar to what you've shown. The 94 series of speakers is a bit confusing with several permutations - - - some of which may have been intended for Euro or U.S. markets only - - - but it's interesting to see that your woofer appears to have a vented dust cap.


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Well, received the speakers last night.

The woofers as suspected are not original :(

Now start the search on some original woofers.

Any idea what part number should I be looking for?

Read here suggested that one possible replacement woofers from AR7 ( I have a pair in which I can try them with) #200001 .

All tweeters seem to be working.

I will try to open up more this weekend to have a look at the crossover board.







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well, on the plus side, they're not some el-cheapo replacement driver...they're some pretty nice woofers, that look to be OEM on snell type J's and other european speakers...

the refoam job looks a bit sloppy, and the foams look like the roll is too small...some filled fillet boston acoustics or large roll JBL foams that are usually recommended for AR 8" woofers would probably work better on these, too...


I'm 90% sure the 200001 woofer in the 7's are the same as the MST's...

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Hi Michiganpat,

The refoam job was definitely very sloppy.

I will take some more pictures tonight of how bad they are.

The foam surrounds are actually much too small for the cones.

The temperature here got to 35C yesterday and we are not equipped for it.

I stayed in the car most of the time as it has aircon :D:D:D .

If I have time, I will look at the XO as well and hopefully they haven't touched it.

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The AR-7 woofer should work well. If I remember correctly there is not much to the crossover -- one cap. The MST1 was reworked considerably. I would upgrade them to the second version crossover given the opportunity.

Enjoy, these may be the rarest of the AR's from that era.


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Agree with the others - - the AR-7 woofer is the appropriate driver - - see pics attached for good examples, although these are the MST-1's (the later three-tweeter version). The speaker on the left was still using the original cabinet with four tweeter cut-outs, but it's interesting to note that when AR built the three-tweet cabinet, the side tweeter was raised to align with the front tweeters.

I'd be curious to know if your cabinets have four or eight T-nuts for woofer attachment and also, please post pics of the original four-tweeter crossover assembly. That's great news that all of your tweeters are in fine shape.

post-112624-0-49302700-1435849907_thumb. post-112624-0-89881500-1435850011_thumb.

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The two schematics are attached. The only thing that puzzles me is that the four-tweet schematic does not show a switch, but perhaps it was not part of that version? Can we also see the back of your speakers?

post-112624-0-10821300-1435852518_thumb. post-112624-0-38822600-1435852534_thumb.

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I will refoam the existing woofers to see how they sound first.

I have a pair of AR7 so I will test with those woofers later.

Is it easy to upgrade it to the second version?

Looking at Michiganpat's link that woofer was designed for bass-reflex cabinets so probably not optimum use. Upgrade doesn't look too challenging. You can leave the fourth tweeter in place as a spare.

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Forgot to take a picture of the back of the speakers but they do have a switch.

I have attached a 'not so good quality' picture of the XO.

Managed to clean up the woofers as much as I can without destroying them.

Glued the surrounds to the cones and will glue them to the baskets tonight.







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Thx for the pics - - you did a nice job cleaning up those woofers.

Your photo of the crossover is very curious. Based on the schematics, I had expected to see a single capacitor for the four-tweet MST, but your image (dated 02/07/2015 ...... how'd you do that?) clearly shows two caps, and it also looks like the number of wires is intended for only three tweeters (plus the woofer, of course). For clarification, if you get a chance, please post pics of both x-o's with a more expansive view.

I know this sounds a little wacky, but I'm guessing you might have original early MST cabinets (and the four tweeter drivers), but with only three tweeters actually wired to a crossover from the later MST-1 (or Improved). If so, you've been furnished with a surplus tweeter in each cabinet that is only serving as a blank-off plate, similar to the first pic in post 13.

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Second crossover pic makes sense, even crossover frequency does change a bit when different switch positions are used...if resistors are in order of 1,5-3 ohms. Is it possible that switch and resistors are located before 10 uf cap?

I hope that someone does have some inside information why side firing tweeters seems to have different crossover slopes compared to direct firing tweeters.

Best Regards


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This is all very interesting - - we can now see that extra brown wire which did not show up in your first pic of the crossover in post 17. While I, too, get confused trying to draw those switches in schematics, I've taken the liberty to annotate your sketch with a few extra clarifying notations and colors, and this drawing (courtesy of RLowe regarding AR-6 speakers) is a very helpful diagram to understand the function of the switch in the circuit.


Basically, with respect to the crossover, it appears that you have a four-tweeter version of the "Improved" speaker (which typically used only three) - - - meaning that two outer side tweeters are functioning more like super tweeters for only the highest frequencies. The front parallel-wired tweets are just like the three-tweet version, but it is interesting to see that the outer angled-side super-tweets are wired in series - - here I am only guessing at the wiring arrangement w/respect to (+) and (-) terminals, but clearly the long brown wire is the one which only connects these drivers and does not connect to the x-o panel.


You may have a fairly unique pair of speakers here, and the interesting question, for more knowledgable audio minds, is whether the initial "performance problem" of the original MST (four tweeters with all same x-o frequency) was corrected in the common subsequent version (MST-1 or "Improved", three tweeters with two x-o frequencies) due to (1) the elimination of one tweeter, (2) the tweaking of the x-o, or (3) both. Regarding your speakers, though, am wondering if you have a rare hybrid pair representing the best of both versions, or does your set have the inherent interference problems simply due to the number and placement of functioning tweeters?


Interesting to see the two blue Sprague caps paralleled, and despite their generally accepted longevity, it may be wise to replace them along with your other 10uF cap, since they differ from each other. The small black/red caps are notorious for having drifted from original values, and since these side tweeters' performance are crucial to your speaker design, replacement of these 2uF caps is probably advisable.


Thanks for the update. Perhaps some of the experienced speaker designers, circuit experts and lab testers will chime in on this situation.


MST schematic.jpeg AR6-3 position switch-Zobel-rara .jpg

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Oh yeah, one more thing that provides simpletons like me with confusion about the switch. The pic attached shows three versions of the MST rear panel, and it is the one in the middle (like yours) that baffles me since it does not move in successive steps - - why is decrease in the middle position instead of "normal" or "flat"?

the three positions are:

* increase = +3dB = 0 ohms in circuit

* normal (flat) = 0dB = 3 ohms in circuit

* decrease = -3dB = 6 ohms in circuit


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I will get all of the caps changed when I get them.

There is going to be a lot of work required.

I need to

1. change the caps

2. find some original woofers

3. replace the grille cloth

4. find the badges as they are missing

Does anybody have some spare badges or have the dimensions for them, a scanned picture would be perfect.

Not have time to work on them tonight.

I will try to put the (seas) woofers back tomorrow and test the sound.

All inputs so far are all valuable.

Thanks all very much.

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