Last week we were playing around in the middle of the vast Silbatone collection of Western Electric equipment. Mr. Mukai and Mr. Yuzo Doi flew in from Japan to visit. These guys are the top WE experts in Japan, both work with vintage dealer/manufacturer/repair shop Western Sound, Inc. and Doi-san is resident WE expert at Stereo Sound Tube Kingdom magazine. All the well-known rare and exotic WECo treasures surrounded us, along with many items that qualify as super-rare or even unique. Prototype Fletcher coaxes with 555s and Jensen 18s, 595As, a couple pairs of 757As, 753s, 750s, L-8 and L-9, every Western horn...plenty to interest any WE maniac.
|Mr. Yuzo Doi --Western Electric set-up man extraordinaire|
working on an early 8b and 9A amp rack at the Silbatone factory
The first day, as discussed in a previous post, we heard the mega-rare 12A/13A system. And what did we work on the second day?...WE 755As. Western Sound Inc has handled a few thousand 755As. Everybody in the room used 755As for at least 25 years. We all have a lot of experience with bigger and more elaborate WE speakers than the 755A but none of us ever got tired of 755As because they are like an element of nature. Nobody tires of the sky.
This humble 8" speaker gets maximum respect from those who know and love it. They were my main speakers for five or six years in the 80s until I moved to a place where I could set up a big horn system with 288s and 1505s. My friend MJ calls it a 10 cylinder car, a hot rod. It is difficult to handle but when you get it set up right, with compatible electronics, nothing else can do what it does.
Lately prices have been skyrocketing on 755As, especially the WE versions, moving them outside the orbit of my wallet. They used to be a "workingman's revenge" speaker but no more. Although I cry about the pricing, I must say that the hype is justified. Not so for the vastly-inferior 755C and 755E, which are good but not fabulous, but when excellence on the order of the 755A is concerned, money is only money...that is, if you've got the money. As always, it sucks to be poor.
In any case, do not think you are getting most of the 755A magic for less cash with a 755C, because you are not. Magic is rare. 755C and E need a tweeter in my estimation and they lack the lightning speed of the A, but they are decent midranges/quasi full-ranges. I am sure there are better single unit full-rangers out now for much lower price than the collector premium on C/E 755s, now up to a hefty $500-700 a pair. Check your local full range forum for suggestions.
Let's not get side tracked on the ancient A vs. C debate. More on the 755A in general later...today I am talking about cabinets.
So I asked Mr. Muhai, "What do you like for 755A boxes?" I meant, what does HE like, using the preference in 755A cabinets as a window into his soul and barometer of his personal taste, but he instinctively answered like a dealer, laying out the field: "There is the Altec 618C, which is made from thin wood so it is very resonant. This is good for smooth sound, easy listening. The Western Electric design was much thicker wood and the sound is more severe."
Severe-- I like that term in this context. I always liked to call the sound of the 755A relentless. It was a monitoring speaker, so if there is a problem with the recording or electronics, you will hear it and you won't like it. If the recording is great, the sound is great. If the recording is OK, it will sound OK, unless it is edgy and bright, in which case it will sound NASTY. On the upside, the severe and relentless character gives the 8-inch incredible definition and detail but you're riding the razor's edge.
The original WE spec for boxes for the 755A, 756A, and 728B called out plywood of at least 3/4" for the 728B and just says 2 cu.ft cabinet. of "rigid construction" for the 755A. They promoted the now iconic slanting front boxes for this line of PM speakers, a design that makes sense for a high mounted wall speaker with the cone pointing down or a speaker on the floor with the cone pointing upwards. I presume it is also beneficial for management of internal reflections to have two non-parallel sides.
Late 40s cabinets built to WE spec have a lot of damping material. In WE literature they specify a minimum of 1" of Ozite, which was the hair felt used as carpet padding in the old days, or Kimsul, which is the brown sometimes slightly waxy or greasy looking* paper material that old tubes, especially big transmitting tubes. were often wrapped in. WE tubes usually come wrapped in thin Kimsul.
Note: Kimsul is not to be confused with Kimchi, my favorite Korean side dish.
[Edit: On further research, I find Kimsul is treated with asphalt, which gives it the greasy look. Kim Sul is also the name of one of Kim Jong Il's daughters :op]
THE ALTEC 618C
The Altec 618C cabinet was a different beast entirely from the WE spec cab...as Mukai-san reported, and it's much more of a boom box. The sides and back are very thin 3/8" plywood and make a lot of noise when you drum on them. The front panel is a bit thicker at 5/8" and far less resonant in itself, but everything is connected so the whole box comes alive while playing music.
|Early 50s Altec 618C cabinet|
With the big Alnico donut magnet on the 755A, the speaker moves air with authority and really excites the cabinet. You can really hear this box and the cabinet vibrations definitely fill out the subjective mid bass presentation.
More than once my wife complained that I was shaking the bedroom floor upstairs with my my loud music. Hey, it is a mono 8 inch speaker and it really wasn't that loud and I was listening to old Sun Ra and Benny Golson jazz, not 80s disco funk. I'm impressed that a 8 inch full range can generate such complaints...just wait till I hook up my GIP 18" field coils.
In reality, Joyce has seen and heard it all. She has 1000s of hours "flight time" listening to 755As. She tells me the speaker has too much bass, adding quickly that she likes bass. She probably means to say "this is one boomy-ass speaker" and compared with most of what I have had around over the years, she would be correct. It has "bass" but it is fake 100 hz bass, this is true.
The Altec 618C has minimal internal damping, which surely adds to the boombox effect. Nothing on the back panel at all. Suspended at a weird angle is a single slab of mineral wool. Actually, it looks like rigid fiberglass sheet like Corning 703 with a coat of varnish to hold it all together and further stiffen it (good trick). That is it.
Whether Altec built them this way for economy, lighter weight, or sonics is unknown. It is definitely a lot lighter than a thick plywood box, a plus for wall mounting or portable use. My 618C has a 1x4" mysterious cutout at the top of the back panel that can work as a handle hole...or maybe it is a port...or both. Certainly works as both, and is a serious deviation from the sealed box spec of Western Electric.
|So much for the sealed box specification...|
There is a tightly-woven metal screen over the cone to prevent vandalism or mishaps and that might have some muting effect on the highs compared with a naked cone. I think the boomy rich character of the box probably makes it a lot more flexible for generic PA applications. Who needs a incisive, hyper-picky studio monitor speaker for a bingo game or high school cafeteria use? From 30 feet out, that mid bass boom probably adds a lot of weight.
THE WSI 618C
Looking around the net, I found some pictures of a 618 type box manufactured by my friends at Western Sound, Inc. which looks to have a late model 409b coax in it. If you do a search on "W.S.I, 618C," you will see this box offered with 755a, 755C, LE8T, and a few other options, e.g. stereosound link.
Very little damping material in these WSI cabs. They like to use the spongy packing paper material that dishware sometimes comes wrapped in as a modern substitute for Kimsul. Hardly enough in there to blow your nose!
Thickness of plywood appears on the order of the Altec 618 box or possibly a bit thicker, maybe 1/2"....hard to tell.* The ply looks to be lower-grade douglas fir with a few knots and voids in it...I am sure this wood selection is 100% intentional, probably close to what Altec used. There are a few more glued-in corner braces than in the Altec original. Screen over cone is in place but back panel is sealed, no handle/port cutout. I'd probably put a gasket on it, but they choose not to. This looks like a slightly beefed-up Altec-type cabinet but it is largely true to the original design.
[* Edit: Yep same as Altec " The thickness of the front baffle is a sound board thickness all 15mm, otherwise it is 9mm It has become the preferred structure."-- from Stereo Sound WSI 618C writeup]
I don't think these guys deviate from proven vintage practice unless they have a good reason to do so.
|Western Sound, Inc. 618 cabinet|
Mukai said that careful individual tuning is the way to match 755A drivers, since it is well known that any two 755As are not necessarily perfectly matched sonically even if from the same era and NOS. Age and use further complicate these matters. Any standard suggestion would ignore the crucial reality that every driver specimen is different.
Maybe the later Altec 618 cabinets are a little thicker and lack the handle hole. I haven't seen one for a long time and I simply don't know. If you have a later model and it differs, send me a pic.
To make a long story short, the vintage Altec 618 box sounds pretty good. A bit over the top with the boom but it works better than expected, maybe better than it should. I know a 1/2" ply box can work well if solidly constructed because I had a few built back in the day, with satisfying results. I'd follow WSI rather than Altec on the details and make the back fully sealed.
My old bud Joseph Esmilla (JE Labs) rescued a snapshot of the discussions the "755 guys" were having in the late 1980s about cabinets, currently found at http://jelabsarch.blogspot.com/search/label/Altec%20755%20Part%202. We used to meet up at hamfests and hash out these amicable disputes while looking for $1.00 2A3s.
Joseph preferred and a popularized an open baffle approach for 755As in a Sound Practices "Homebrewer of the Month" feature and on his website (link--see also open-baffle link). One of the first US open baffle advocates.
I tried the open baffle and it did not float my boat. As he reports in the webpage, I rejected it for not having enough dynamic excitement, which the 755A excels at. Yeah, it was open and airy but no cojones. He mentions that I complained about no "snap"--I still like that term. Gotta have the snap.
I also missed the bass with the open baffle. Obviously, 755As don't have very much LF extension to begin with and I needed whatever I could get. In a sealed box sited against the wall for maximum boundary reinforcement, there are hints of 45-50hz bass that do a lot to fill in the missing parts of the picture. I'd say it implies these lower frequencies better in a sealed box, although it doesn't reproduce them in any convincing fashion no matter what the enclosure looks like.The 755A is really good at leaving out things that it can't do in a way that keeps the music going.
One exception to the 755A bass is my Korean friend's back horn enclosure. The dude is a divinely-inspired master at back horns, designer of the Silbatone Aporia and SGW-24 horn system that we took to CES a few years back. His 755 cabs fill up a large room with powerful and solid bass down to at least 45hz, an amazing accomplishment, but I feel that these backhorn cabs throw the highs under the bus to get there. They let the 755A play big orchestral, but at what cost?
755As have a really special high end, if not particularly extended in that direction either, and bringing in more bass skews the delicate balance that the orthodox 2 cu.ft. sealed box delivers. If man were meant to fly he'd have wings and if the 755A was supposed to have bass it would be a 15 inch. Don't mess with Mother Nature!
Joseph also published plans for a box that sort of leans toward the WE spec, rejecting the 1/2" ply version as too slow. He says to use 5/8" ply "the more resonant the better" which is a bit of a punk out on the WE standard. Factory spec WE boxes are solid as a rock and quite non-resonant.
|JE Labs box plans - same dimensions as Altec 618 specs.|
You can see he also gives cutout dimensions for front and rear mount. Walt Bender, the main guy to popularize 755As back in the 80s, was a big fan of front mount and he promoted a design that was 2 cu.ft, with a 1/4" or 3/8" Plexiglas or Lexan plate on the front. You have to be careful to provide clearance for the holes on the side of the driver basket, hence the thin plastic panel. As I recall, Walt liked 1/2" plywood with the front mount arrangement.
I had a beautiful pair like that I traded from Vinny Gallo -- dense 1/2" marine ply with silver hammertone finish on the wood and plexi. They were some of the best 755 boxes I had, until that lying rat bastard borrowed them "for a few days" back in 1989.
Rear mounting a driver on a thick baffle seems like a really bad idea but it sounds quite good. More hearty and thick sound than front mounting, which is a lot more open and seems to promote stereo imaging better, making for a more lively and upfront presentation. In a sense, the the thinner wood fattens up the sound and so does rear mounting, Front mounting and thicker plywood make the speaker a bit faster and crisper...balance those parameters as you see fit. Don't forget a healthy round-over on the edges of the speaker cutout!
I'm getting a pair of new boxes made right now and I've been struggling with these eternal questions. I'm thinking I will go with 5/8" ply and Baltic birch, because my cabinet guy strongly prefers working with this high quality stock and there don't seem to be many choices for 5/8" around here. I'll start with old school rear mount. I can later cut a larger hole and add interchangeable Lexan or linen phenolic mounting plates that will allow for either front or rear mount.
I'll probably flip my original 618C box on ebay since I only have one unit and now I have a pair of Altec 755As. After soaking up the 618C sound for some months, I think I can do better for my current taste with 5/8" ply anyway.
However, something tells me this is not the last pair of 755A cabs that I'll commission...I'm already thinking I should have gone with 1/2" ply!