Vintage Asylum

Altecs were "Duplex" rather that coaxial but

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kavakidd

In Reply to: RE: Coaxial kits -1950s posted by J. Phelan on March 24, 2016 at 10:25:08

I can't tell you how they differ
"Man is the only animal that blushes - or needs to" Mark Twain

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Just a name; the Duplex is a coax two-way loudspeaker - mhardy6647 06:19:53 03/25/16 (6)
I think that the Duplex -- introduced originally in the early/mid 1940s, about the same time as Paul W. Klipsch's "Klipschorn" -- MIGHT have been (???) the first commercial, purpose built coax design.

(I THINK it predated the Tannoy coaxials?!)

(next time, I need to dust the horn cells BEFORE taking a photo of one of those!) :-P

all the best,
mrh
- RE: Just a name; the Duplex is a coax two-way loudspeaker - J. Phelan 07:16:46 03/25/16 (5)
  Great info -wow ! And historically important -at the birth of the hi-fi era.
  
  You're right about Altec in the 40s. But (I don't think) in kits until the 50s, along with Jensen, etc.
  
  And I see they were not compression drivers. But still a lot more affordable than corner horns or ESLs, of the day..
  - the Duplex's HF unit was (is) a compression driver - mhardy6647 07:22:45 03/25/16 (4)
    As I understand it (and my understanding is meager), the 604 was, in essence, sort of a 515 LF unit and sort of a 288 HF unit in one package.
    
    I love mine (604Es). Listening to "On Point" on FM radio via mine even as I type this, in fact.
    
    all the best,
    mrh
    - http://audioheritage.org/html/profiles/altec/duplex.htm (Open in New Window)
    - RE: the Duplex's HF unit was (is) a compression driver - J. Phelan 07:53:59 03/25/16 (3)
      I see...
      
      But not the typical horn driver -say a 1-2" dome handling the mid-frequencies.
      - the crossover is at ca. 1100 to 1500 Hz (depending on the specific version) - mhardy6647 12:08:20 03/25/16 (2)
        
        In Reply to: RE: the Duplex's HF unit was (is) a compression driver posted by J. Phelan on March 25, 2016 at 07:53:59
        
        Not sure we're on the same wavelength (pun partially intended).
        
        The Duplex is a true two-way speaker, although most versions lack considerable HF extension due to the horn and the XO design. That's just one of those things. The diaphragm on the treble driver in a Duplex is fairly big; again, I think it's similar to (although not identical to) the famed, venerable (and EXPENSIVE) Altec 288 compression driver.
        
        A dome MR per se would be far less sensitive than the woofer or HF driver used in the Duplex. The Duplex's HF driver and horn might be best thought of as a MR horn, but as you can tell from the XO frequencies (in the subject line, and from memory, so I may not be dead on the range used by all Duplex versions ever made/sold) much of the MR was handled by that big, 515-like 15" driver and its paper cone and pleated (accordion) surround.
        
        I like to say that the Altec 604 series Duplexes are the best midrange drivers ever made :-)
        
        Now, back to that crossover: Time alignment of the original Altec XO was, arguably, the big "opportunity for improvement" of the Duplexes of yore. Doug Sax "MasteringLabs" sold one that was widely used (and, IMO, quite effective) in studios.
        
        Jeff Markwart has also designed improved XOs for some of the Duplex drivers. See link below.
        all the best,
        mrh
        http://home.earthlink.net/~jmarkwart/ (Open in New Window)
        
        RE: the crossover is at ca. 1100 to 1500 Hz (depending on the specific version) - J. Phelan 12:36:42 03/25/16 (1)
        
        In Reply to: RE: the crossover is at ca. 1100 to 1500 Hz (depending on the specific version) posted by mhardy6647 on March 25, 2016 at 12:08:20
        
        So we're talking a 6" compression driver ! Much larger than they use today. Back then, they used dynamic-cones (as compression-units) as well.
        
        Then, the horn itself. Western Electric's 757-A, from the late 40s, didn't need to re-inforce its driver with 'butterflies' (like the RCA LC-1). Because it used an actual horn in its design.
        
        no, the diaphragm is probably about 2.8" in diameter - it's NOT a direct radiator - mhardy6647 15:05:21 03/25/16 (0)
        
        In Reply to: RE: the crossover is at ca. 1100 to 1500 Hz (depending on the specific version) posted by J. Phelan on March 25, 2016 at 12:36:42
        
        Spec sheet for a more modern 288 below; VC is 2.8 inch; I presume the diaphragm is roughly the same (since they're basically a unit).
        all the best,
        mrh
        http://www.greatplainsaudio.com/vintage_altec/288-G%20Series (Open in New Window)

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