Vintage Asylum

RE: the Duplex's HF unit was (is) a compression driver

76.28.27.191

J. Phelan

In Reply to: RE: the Duplex's HF unit was (is) a compression driver posted by mhardy6647 on March 25, 2016 at 07:22:45

I see...

But not the typical horn driver -say a 1-2" dome handling the mid-frequencies.

Follow Ups:

the crossover is at ca. 1100 to 1500 Hz (depending on the specific version) - mhardy6647 12:08:20 03/25/16 (2)
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)
  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)
    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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