Altec 2 Way Build ala JELabs - 802/32/414

Discussion in 'High Efficiency' started by marantzfan, Mar 8, 2018.

  1. Thanks Joe… I’ve seen your various autoformer hacks, but can you point to a “real” auto former whether vintage or new or just comment on what you’ve been using?

    JE reminded me and It might be helpful to explain one difference between the 15” woofer variants and the 414’s is that the 414’s are running full out up top.
     
  2. I have tried a few Triads, Peerless, and those Werner jobs, plus a few other old stock autoformers and two winding transformers.

    An autotrans is a single-winding transformer, basically. Some speaker matching units are actual two-winding transformers.

    The advantage of Werner's is that they are purpose designed whereas the taps are like 2-4-8-16-32-125-250-500-2000 on commercial units, not much granularity. Werner's have plenty of resolution on the attenuation settings.

    Werner units sound far better than any of the vintage units. The Magnequest TL-404 autotrans (also on C core) is also really good sounding but doesn't have the fine steps of the Werrners.

    I was tempted to snag some Slagle nickel jobs once I totally figure out my preferred ratios and such, but really I'm totally happy with the Werners. I can't help experimenting though. I gotta stop.
     
    TubeHiFiNut likes this.
  3. marantzfan

    marantzfan Administrator Staff Member

    And the plot thickens...

    I’ve got a decent handle on how I’m going to build and attach the face frames now. So the “how to” on cabinet assembly is coming into focus.

    I’m not buying any crossover parts yet. I’m really curious to see where this conversation leads.
     
    SPL db likes this.
  4. I’ve unpacked my late (MDF, fixed panels) 614 cabinets to take see if I could convert them to 9849 cabinets. As luck would have it the 414 is centered more in the 614 than the 9849 so no go. However, I did take a closer look at the factory 614 cabinets and made these observations:

    1. They are made of 3/4” MDF, with one cross brace on the front and rear panels.
    2. They are 24” X 20.5” X 15.25”. The front port is 2” x 7”. There is an inset grill (which I do not have).
    3. They are appear to be lined with yellow fiberglass bat (2”?) on all sides.
    4. There is a yellow fiberglass bat installed diagonally from the top front to the back rear.

    It seems the factory engineers knew What they were doing.
     
  5. Those 614s are probably made out of particle board not MDF.

    Some say particle board is actually better than MDF thanks to being variable density, less dense in the center of the board than on the outside edges. I don't have any dog in this hunt, preferring plywood with Altecs.

    The basic design goes back to the early 30s Lansing Iconic. About a 50 year career.
     
  6. Philosophically I prefer plywood as well, but since these came that way I have no problem. I was actually pointing out that Altec applied the rigid insulation bat trick in their enclosures dating back at least to the 1970's. I'm finding that a lot of classic manufacturers employed a lot of techniques we are employing today.

    Aside from Altec 414's, I also own a pair of Goodmans Triaxiom 212's. I would guess they are similar in spec to the Altec 414A, albeit with a whizzer cone and concentric horn tweeter. Of particular note are the enclosure recommendations for the drivers.
    • The standard enclosure is 12,500 cubic inches (7.23 cu ft!) with a pretty large port.
    • An alternative enclosure is 7,800 cubic inches (4.5 cu ft - pretty ideal for a 414A), using an ARU Acoustic Resistance Unit (10" x 10" aperiodic vent). The appealing aspect of this is that one could swap out baffles on this enclosure and use it for a Goodmans 212 or an Altec 414/32A. It would also make me wonder if the ARU enclosure would also work well for the Altec.
    • In all the recommended enclosures, Goodmans recommends hanging 2 felt curtains behind the driver. This seems to be a popular approach among high-efficiency factory speakers of the era (1960's). I know the Diatone 2S-305 used a variation on the back wall (felt that was folded against the back wall https://www.ebay.com/itm/Early-Mode...m=121560521545&_trksid=p2047675.c100005.m1851). I think with light coned, efficiency drivers it is important to control the back wave coming through the cone.
    This has also made me think more about open baffle/aperiodic loading. If we mount our removable baffle in a frame a few inches deep, we now have an open baffle speaker. I've also been thinking along similar lines as Joe - we can line the back of this open baffle "enclosure" with a large aperiodic vent, say a piece of 2" absorptive material. This could potentially knock down the back wave enough to make the speaker more manageable in the smaller room while retaining the openness of the speaker. This is not dissimilar to the approach used on my old ESL-57's. They were open dipoles, but the back wave was tempered by felt/coir on the rear of the speaker. Some people take that out. I didn't.
     

  7. I had a c.1953 618 with a slab of Owens Corning 703 rigid fiberglas across the inside and only a small rectangle of fiberglas on the back panel. That was a very lively box.

    The original Lansing cab had "pillows" stuffed with dense filling that extended about 8" out on several sides, getting the damping material out into the central cab space where velocity is higher. I'll look for a pic.
     

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