Altec 755a's

[Joe Roberts]

I had the original Altec box like that. It was "OK" but various boxes I had made out of 1/2" ply over the years were less obviously thin wood contraptions. Sold the originals to the collector market. I'm a user, not a collector per se.

I wrote up the original 618 box on my blog, which is admittedly somewhat infrequently updated.

The Bae box is probably better than the slant wall cab approach, which is why I bring it to my 755 Bros' attention. If you're running C or Es. there's not much room for a tweeter in this box though. With As, it is killer. Never tried it with C/Es. but i always downplay the merest comparison between those and 755As, so that they do not become confused or conflated with 755As.

Anyway here's a pic of the inside. Fully lined with Kimpak paper insulation and wired with pure silver litz wire we use in amps and for whatever.



I'll provide a crude sketch when I get the pdf file small enough to upload

 

[Joe Roberts]

While I have yet to hear these speakers in a proper cabinet, I can already see some of their good points, but the lack of bass does bother me.

a) it is an 8" paper speaker from 1948, so it will never be a bass monster choice, no matter how good it is at what it does.

b) You haven't even heard what it can actually do on the low end, which is never going to shake the walls but it does the job of getting the music across in a very vivid and engaging manner.

I never felt the need to add a sub. If I want to hear the cannons on Telarc 1812 or rock out with Sly and Robbie bass jams, I play some other speakers, although the 755As will still do a reasonable job for 8" paper cone full ranges if I am too lazy to switch.

The 755A has just the right proportion of lows and highs, not extended much in either direction. it is balanced.

If you add low bass, then you will want a tweeter to address the subsequent imbalance...at that point you might as well go buy a Magico or something.

Why head down the path of a poorly-matched three way? You can do that with inexpensive Parts Express drivers, don't need 755As for that.

 

[Olddavid]

Joe, is that a decreasing volume port, a la BIC Venturi? Beautiful cabinet work from what I can see. Very nicely done on the radius of the port entry and cabinet corners. Phil, you risk being burned at the stake by purists. The one man who I thought would have these stashed, does indeed have a set, that he installed in sealed cabinets. I always thought Altec and anything done by Klipsch, Lansing, et al, was better ported?

 

[Joe Roberts]

Yeah, David, that is a flared port but the box is NOT TUNED. It is basically a small box with a hole in it.

Dr. Bae came up with it via empirical experimentation, or so he says. I suspect he flared the port to avoid turbulence at input and output arising from abrupt terminations, but it is all seat of the pants engineering as far as I know.

The guys in Korea got hold of a popular Japanese cabinet that was larger than this box and I think it had an untuned port of some type. Bae thought it was too boomy so he made a few smaller versions.

The 755A is a last generation Western Electric design, not an Altec design. This was offered as a general application high quality speaker. Requiring a tuned bass reflex cab gets complicated if you want to put them in the walls of an aeroplane, ceiling of Macys. etc.

The WE cabinets of the late 1940s using the 7XX drivers were usually sealed box, including studio monitor grade and auditorium systems. Early Altec cabs after the inheritance of the WE designs were sealed box for the 8 and 12" full range speakers they offered, pretty much the slant face wall cab pictured above. Altec Bass reflex picked up steam in Hi-fi cabinets, although it was a feature of Voice of the Theater cabs from the start.

I and my friends have tried to run 755As in tuned bass reflex cabs but the problem alluded to above about balance rears it's ugly head.

These have just enough bass and just enough highs to do the job. Skew response in either direction and the tonal balance is gone.

Frankly, these touchy suckers are hard enough to get just right in a sealed box.

A small bass-light cab might be OK for voice PA use but for music, best to use it as a full range single driver as intended.

Anyway, see if you can borrow those 755s! Check them out. If you guys don't like 'em, you can always give them to me!

 

[Joe Roberts]

Here's a rough sketch of the Bae cab.

 

[phil-g]

This is the article I got a few suggestions from. Good read, I thought.

http://jelabsarch.blogspot.com/search/label/Altec 755 Part 2?m=1

 

[Joe Roberts]

Oh, THAT dude...always copying my stuff, right Mr. Setup1??

No only joking. Joseph is The Man. A DIYers' DIYer. Homebrewer of the Month. Very generous and helpful individual, constantly cranking out old school projects like a possessed maniac. I just saw his new loktal tube EAR 834ish preamp build on another forum.

I offered to give or lend JE whatever he needs, i.e., parts give, WE speakers lend, if he promises to share his findings with the people.

He helps a lot of people out with his advice column for vintage/DIY experimenters.
Anyway, the jelabs man is a participant on this thread, quietly soaking up material for his next informative blog post!!

 

[Redboy]

I bought some Kimpak... but my weekends got booked up for the rest of the year. Typical.

 

[elitopus]

Where is the best place to buy the Kimpak? And is it different that Versa-pak? Both are cellulose wadding

 

[Redboy]

Got mine on eBay. I think Versa-pak is Kimpak, rebranded. Or vice versa... I dunno.

 

[Joe Roberts]

Try looking up Kimpak on google. Amazing how many Koreans are named "Kim Pak."

One of Kim Jong Il's wives or sister, somebody in the family anyway, was named Kim Pak...seriously.

Pure coincidence that Silbatone uses a product that sounds so Korea friendly.

Kimberly-Clark sold off that product line, now called Versa-Pak. It originally had the K thing going on like other Kimberly Clark brands--Kotex, Kleenex, etc.

Now it sounds more Pakistani-friendly.

 

[elitopus]

That's good stuff. Lol

 

[scoville]

So, are the 755 b&c constructed of the same Silk Blend as the a? I'm guessing Altec changed the cone materials when they ran out of the WE cones. I'm still searching for someone to repair the VC. I do have a lead, wish me luck!
Thanks for the Silbatone info Joe!

 

[Joe Roberts]

Well, I recently talked to a guy in the business who had a 755A cone analyzed. NO silk in it. Basically hardwood pulp. So I don't know what to think of the long told story about the silk recipe. Walt Bender started that tale, I think.

What Mr. Doi of Western Sound Inc., probably the biggest 755A nut/expert on the planet, told me is that ALL 755A cones were from the original WE batch. When they ran out, they switched to the ferrite C/E. He further went on to describe how the 755A cones are multilayer/variable thickness, You might be able to see this where yours is ripped. They tend to split horizontally at the edges, which is not what paper usually does. According to Doi-san, the C cones were not as complex to manufacture but not as stiff as the original.

The C is 8 ohms vs the A 4 ohms. And according to my Woofer Tester, it is a very flat 4 ohm impedance with a very moderate rise at HF, very special. Low inductance vc, I think.

And the suspension is looser on the C.

The later versions are very different from the A. They have the same number and are suitable for the same sorts of PA installations but that's about it.

 

[scoville]

I obtained a new cone, supposedly from the same, original mold. The original is a different color, and feels thinner. Very light, and fragile. I'm really not sure how one would go about attaching the cloth surround.

 

[elitopus]

Did you get the new cone from Springfield Speaker? Their ad claims they use the same exact mold as WE did in 1947

 

[setup1]

Hey Joe,

Thanks for sharing the Bae/Silbatone 755A cabinet dimensions! Concert season starts next week, so this 755A cab project will have to wait.

JE

PS: Looking forward to your blog updates

 

[Joe Roberts]

I'm really not sure how one would go about attaching the cloth surround.

Well, that's just it. A 755A does not have a cloth surround. It is all paper.

C/E have the accordion cloth surround.

I'd send the parts to a pro for best results. With the enclosed basket construction of 755s, they are kinda challenging to work on.

I've been hearing about those "original molds" for several decades from various people. Nick, the founder of Lambda Acoustics, was the first one I encountered who knew where they were. There were also several aftermarket makers and they all had molds too. Who knows the real story?

I hope those cones are good but I also hope I never have to find out.

PS: Looking forward to your blog updates

Don't hold your breath.

After some weird experiences with some crazed dude on a different thread, I am about to go back into hiding for a few more years, smoke a pile of legal weed , and listen to my Baebox 755s.

 

[lordgarth]

Those Altec 755a's are for low income people. This is what you want;

 

[Joe Roberts]

Send it on over, bro. I'll give you my Fedex account number.

I compared Altec and WE 755As numerous times. There is absolutely no difference.Those silver WEs look very sexy though.

Actually, there is one constructional difference...the space in the magnet under the rear vent cover is stuffed with paper (Kimpak) in the WE and fiberglass in the later Altecs. i won't pretend to hear the difference here.

Anyway if you were really rich you would have an actual WE manufacture amp, not a shitty KS amp!