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AR-MST, ideas?


ra.ra
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Rather long-winded here, but....

My two take-away thoughts from this experience are: 1) you just never know what might turn up in the most unexpected place, and; 2) sometimes there is comedy and tragedy within the same tale.

Yesterday I was exploring a South Boston warehouse for modern furniture, and very soon thereafter stumbled upon a totally different industrial building with a hand-painted "Saturday flea market" sign leaning against the fence. Unlike so many places within urban Boston, parking was easy and available, so what the heck, let's take a look-see inside.
The place was cavernous and gloomy with no natural light, and the only other things that held any attraction for me were a full set of 50's metal kitchen cabinets and a pre-owned golf club, both of which I passed on. But what really caught my attention was a lonely orphan AR-MST speaker, sitting rather uncomfortably amongst some hideous Rococo dining room hutches and buffets.
Upon closer inspection, this really isn't much of a speaker to speak of.....so to speak. Curiously, this "find" seems to be an original four-tweeter MST cabinet which I am sure never left the factory as a finished product. The 3-sided hinged linen grille is present (condition: decent), as are twenty T-nuts, and the cabinet has a layer of thin fiberglass stapled to most facets of the interior. Otherwise, no drivers, no crossover components or rear panel, no wiring, no switch, no terminals or front badge. Speckled paint on backside, most likely intended for Euro market.
Oops, I stand corrected by my own pics.... what I meant to say was "no original drivers". This specimen, which I did purchase (no sympathy required - - - it was almost free), had a single 8" co-axial driver which had zero screws holding it in place, flopping around like a fish in a boat, but at least it did have a long tail of attached brown lamp cord (huh?). The tweeter openings were all covered with what looked like war-zone bandages, swatches of fiberglass insulation taped over the cut-outs. Yikes!!! ...... although it's been well-documented that classic AR speakers are not particularly attractive with their clothes off, this one just might raise the bar for ugly.
Appalled and aghast yet?.... but truth be told, that was actually the comedy portion. The tragedy now appears in Act II. Gleaned from rapport with the merchant, I soon learned that this semi-skeleton cabinet was a loner on the sales floor solely because it was so very fortunate to include this single "speaker". Mouth agape, jaw dropped, eyeballs rolling backward, I was informed that the other three similar (and entirely NOS, still in plastic wrap) cabinets were recently relegated to the dumpster (long gone, yep, I was willing to dive) because each of them did not possess said desirable speaker driver, and therefore, were deemed worthless. Sigh...
What's past is history, so let's look to the future. The central purpose of my post here is that I am just fishing for thoughts about how I might best use this unique cabinet. I am reasonably familiar (but no expert) with the 3-tweet and 4-tweet versions of the MST, but clearly, this speaker model had its (limited) success and failure in two-channel stereo mode. With only one cabinet, there simply ain't gonna be no typical stereo with this project.
My thoughts, thusfar. With a four-tweet cab, I do have more options than a three-tweet cab might offer, at least regarding tweeter placements. My limited inventory does include several versions of 8" AR woofers (cloth and foam, alnico and ceramic) as well as several 1.25" tweeters (ferro-fluid and not), so I do have some in-family drivers that will fit the baffle cut-outs and just might "play well with others". With only one cabinet, one consideration is to construct a symmetrical "center" channel which could then fit to my 60's HH Scott tube amp which does have taps for this feature. I really just don't quite know what to do with this, but I'd like to make it operable within the general spirit of the original MST products. If this center channel idea might just be a feasible notion, how might I try to fabricate this completed speaker - - - more like the 3-tweet version (two x-o frequencies) or more like the 4-tweet version (one x-o frequency)? .... or something else unique in between?
Thoughts and ideas welcomed and appreciated.
post-112624-0-56815800-1404093774_thumb. post-112624-0-53105900-1404093790_thumb.
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A few other thoughts and pics....

Cleaned up the cabinet just a bit, and then loose-dropped in a few drivers just to generate ideas.

It occurred to me that I've never seen any company literature or schematic for the 3-tweet MST (MST-1), but I am now attempting to put together a sketch for comments, based on pics I've seen of the crossover components. But still, there seems to be no information on the amount of cabinet stuffing or even the cap values for the tweeters.

Not particularly germane to my particular objectives but equally curious to me, AR literature suggests that the cabinet volume of the MST is equivalent to the cab volume of the AR-7. At first I thought this couldn't be true; then I placed an AR-7 atop the MST and saw that their cabinets depths are identical and their horizontal cross sections appear to be nearly the same. But then I reconsidered again - - when the third dimension (height) is accounted for, the MST cabinet is more than 4 inches taller than the AR-7. Are these published cabinet volumes fact or fiction?

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Find the landfill that dumpster went to!

I did not know Scott tubes amps had a center channel output but that sounds perfect to me.

Don't know nothin' 'bout no bluetooth but maybe Pro could expound a bit.

Any interest in making a mono system for somewhere?

Have fun with this.

-Kent

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A mono system is just what I was thinking about, Kent.

Matched with a Bluetooth receiver board and a compact internal amplifier, the MST would be the modern equivalent of a good old table radio, but with much better sonics.

Pair up your cellphone as a source, and you're in business.

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"Don't know nothin' 'bout no bluetooth" basically applies to me as well, but the idea of a separate mono system does have some appeal. I have been trying to learn about some of these tiny inexpensive T-amps that seem to have quite an enthusiastic following, but my knowledge of new-fangled audio gear and compatibility is seriously lacking.

Re: outfitting the cabinet, I'm beginning to think about a hybrid MST - - - maybe a four-tweet version with two crossover frequencies? If that, would the super-tweets be located on the angled side panels? Any ideas on the cap values from the original MST-1?

Attached is view of Scott 222-D speaker terminals.

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Not knowing anything about Bluetooth receiver boards, I did find this, which was quite educational.

http://www.youtube.com/watch?v=z4DtZx1oxcA

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From viewing photos only, this is my best stab at creating a schematic for the 3-tweet MST-1, with C-1 serving all tweeters, and C-2 only for the side tweeter. Any comments on the wiring, or known values for the capacitors?

post-112624-0-09949700-1404234620_thumb. post-112624-0-95824600-1404264525_thumb.

7.1.14 edit: added pic of crossover.

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From viewing photos only, this is my best stab at creating a schematic for the 3-tweet MST-1, with C-1 serving all tweeters, and C-2 only for the side tweeter. Any comments on the wiring, or known values for the capacitors?

attachicon.gifMST.jpg attachicon.gifAR MST1 xover close up.jpg

7.1.14 edit: added pic of crossover.

Attached: 3-tweeter AR-MST Crossover Schematic.

--Tom Tyson

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Thank you, Tom, that is the first time I have ever seen these components identified in a schematic. My sketch was almost correct - - looks like I just need to re-direct one of the 3-ohm resistor leads to the center terminal of the switch.


Regarding the switch, I assume the one that the schematic suggests is a 3-position switch, as shown in the crossover pic and these rear panel views of the MST-1. If so, I'm leaning toward something like this single-pole, double-throw (SPDT) mini-toggle rated up to 6 amps.


And, if I wanted to create a four-tweeter unit with the two separate crossover frequencies, would I simply add another of the same driver on the other side panel and wire it in parallel with the other side tweeter (after the 2 mfd cap)?


post-112624-0-72247600-1404326061_thumb. post-112624-0-09802600-1404326084_thumb.

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  • 5 weeks later...

Another month evaporates, but very little progress to report on this project. Nevertheless, other questions arise, and once again I seek advice and opinions from the collective brain trust.

Woofer. As you can see, my initial intention is to use this damaged AR-7 woofer - - the cone was torn in transit due to inadequate packing (not altogether catastrophic, relatively speaking, since the matching woofer fell out en route and never arrived!). My attempt to repair the cone (with fibrous paper on backside, courtesy of sage advice from Bill Legall), is not particularly attractive but I think it just may perform satisfactorily. My question here is about 8" foams - - - I have several 8" AR woofers needing re-foam, and while I've always been very pleased with service and product from M Sound, I know that John has been challenged keeping up with customer requests. So I guess my first question is: are there other recent preferred products and vendors for foam surrounds for 8" AR woofers?

Stuffing. This MST cabinet already has some FG stapled to backside, but how much more to add? Still can't believe MST cabinet volume is identical to AR-7 (see post 2), but is there a quantifiable measure for this material? More FG, or poly-fill?

Capacitors. Originally, I simply assumed I would install two new polypropylene caps, but now I want to ask about polyester caps, which I understand may offer performance (due to higher ESR) which more closely complements the original speaker voicing which used NPE caps. My thoughts include something like these German ERO Roederstein (green, in pic of random assortment) caps, which I believe to have a polyester dielectric; or maybe Carli caps from Madisound?; or maybe Mallory 150 caps?

Thoughts, advice greatly appreciated.

post-112624-0-50444900-1406949214_thumb. post-112624-0-52994700-1406951019_thumb.

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  • 6 years later...

MST Mk II (three tweeters)
Woofers DCR: 4.5 & 4.5
Tweeters DCR: 8.8, 9.4, 9.8. 9.9 10.0, 10.1

I replaced the two front tweeters capacitors out of specs, but the voicing has changed for the worse.
As the knowledgeable members of this distinct group say, a precise value in μF is not necessarily going to make your day.
I replaced them again with a cheap alternative I had on hand and now I'm much more satisfied.
I keep comparing them with AR 6 (reference) and AR 7.
I still get a bit too much of shrill hi-mid (the low-frequencies are gorgeous). The 3-way switch is on Normal.
Should I settle down with this result?
Pic: yellow no good, white ok

DSCN1683.JPG

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