Altec 604e Crossovers

Discussion in 'High Efficiency' started by Wash&Dry, Feb 21, 2016.

  1. Wash&Dry

    Wash&Dry Junior Member

    I have a pair of Altec 604E's that I am putting together and I am missing crossovers. I'm hoping someone can steer me in the right direction. Since Jeff Markwart never made a XO for the E's what do you guys think about trying to create my own n1500a's. Or should I save myself the headache and just buy the crossovers that GPA sells Any input would be great. I did come across these pictures that looked pretty helpful were I to try to re-create the n1500a's.
  2. mhardy6647

    mhardy6647 Señor Member

    Unfortunately I am not an expert at all on this topic (although I should be!) but, since you haven't gotten a response yet from someone who is, I'll offer what little I've got.

    The original N-1500 crossover from Altec is widely reputed to be flawed in its integration of the two drivers, resulting in the Duplexes "shouty" aggressive character as decried by some. The MasteringLabs crossover was, it is said, designed to correct the flaws of the Altec XO, and is what I use with my 604Es (despite my having no idea as to whether or not this specific design is appropriate for this specific Duplex).

    I don't know if the current GPA XO has addressed the ostensible shortcomings of the Altec XO (one would think/imagine/hope so)... but I guess my paltry offering would be "why not just seek out a pair of the MasteringLabs XOs?" My 604Es are quite smooth by (edit) many folks' accounts (not just my own, biased one) and -- while midrange-forward in that quintessentially Altec way :-P -- aren't what I'd consider overly aggressive. (Klipsch Cornwalls would be a good example of loudspeakers that I'd consider "overly aggressive" if that helps calibrate my assessment at all).

    [​IMG]604Etest by Mark Hardy, on Flickr
  3. Wash&Dry

    Wash&Dry Junior Member

    Thank you for your response Mhardy. I will keep my eyes open for the Mastering Labs XO. They seem somewhat rare, I have only seen them for sale once. Perhaps in the meantime I'll experiment. What the heck I don't want them to sit idle...
  4. mhardy6647

    mhardy6647 Señor Member

    No. No, you don't. ;-)

    [​IMG]DSC_8059 by Mark Hardy, on Flickr
  5. marantzfan

    marantzfan Administrator Staff Member

  6. mhardy6647

    mhardy6647 Señor Member

    I thought I remembered he had a page on the 604E...

    <Now, Marky sticks his hands in his pockets, looks down at the floor, and starts shuffling his feet...>

    So... there are two things that I... I don't quite understand about the 604E.

    Thing the first. The E was spec'd (advertised) as "8 to 16 ohm". Is that just a rebranding of the earlier drivers' "16 ohm" impedance to suit a market that was drifting towards amplifiers better matched to lower load impedance, or was the E actually different electrically/mechanically as regards its nominal impedance? I suspect the former... but I don't know.

    Thing the second. Based on my non-scholarly review of datasheet scans posted on the internet :-P I am under the impression that there were 604E speakers labeled "Duplex" and 604E speakers labeled "SuperDuplex". Is there any difference between the two besides the labels?

    (I wouldn't admit to such naivete just anywhere, of course -- but I'm sure my secret's safe with you all!)


  7. Wash&amp;Dry

    Wash&amp;Dry Junior Member

    Very interesting questions. Yes it is quite peculiar that the E is the only one that states it is designed to operate at 8 or 16 ohm. None of the other 604 line states this. They all specifically state one or the other.

    Also I never realized their were both Duplex and SuperDuplex speakers. (I'll stand behind your naivete). I don't really see a difference between the two. Very strange.

    Marantzfan, do you have a preference in oilcap manufacturer? And do you know what a MF EQ circuit Markwart refers too? Or how it would fit in the schematic?
  8. Kyle

    Kyle Junior Member

    My measurements for the 604Es that I had a while back were 11.5 and 11.9 ohms on the bass section which would be consistant with a 16 ohm speaker. 8 ohm speakers are most often in the 5 to 6 ohm range. I believe Altec touted them as 8 or 16 ohms for marketing purposes. Similarly, the Duplex and Super Duplex were visually identical other than a nicer sticker on the Super version.
    The crossovers were not the most sophisticated and likely would not have had a big difference when used with either 8 or 16 ohm speakers. The other thing is that the horn for the 604 is too small and only provides loading down to about 1800 Hz even though the crossover is centered at either 1500 or 1600 Hz depending on vintage.
    That said, I've owned three different versions of 604s and they all had the ability to play music in a winning manner.
    I too am an Altec guy, but without the rigid belief system. 19s baby, 19s!
  9. marantzfan

    marantzfan Administrator Staff Member

    I've read a bit about the 604/605 series, and in this instance, it's the 605 that is causing the differentiation.

    So, from what I have heard, when the 605B was the current Altec Duplex offering, there was still a pretty vocal studio outcry for a return to the 604, as it had been discontinued at that point in favor of the 605. In order to maintain the 605 as the new standard for the duplex driver, when the 604e was reintroduced, it was under the moniker of "super duplex" so as not to discredit the 605b in Altec marketing speak.

    This at least, is what I have heard from various Altec folks.
  10. billfort

    billfort Administrator Staff Member

    Wash&dry, seems you are up against the crux of the problem with the 604E - I don't think anybody has shared a simplfied version of a crossover for them that incorporates MF EQ - which IMO is absolutely necessary for getting the most out of 604s.

    I've heard (and loved!) the 604E on several occasions but they were always on Mastering Labs crossovers - the design of which is out there but daunting in it's complexity and use of a custom built multi-tapped choke. Lots of into on it here and I've attached a doc I found that details it a bit more.

    Not sure where to go with 'incorporating MF EQ' into the original schematic as I'm no circuit designer but do have much respect for Markwart's opinion - I use his crossover design on my 604-8Gs and love the results; too bad he has never tackled and published a circuit for the E.

    Attached Files:

  11. mhardy6647

    mhardy6647 Señor Member

    Wonder if we could start a special-interest group or PAC to lobby him (Markwart) so to do? ;-)


    The funny thing about the 605 -- as far as I can tell, their only real "fault" from an industry perspective was their lower sensitivity compared to the 604 family. Seems like a straightforward thing to "recalibrate" but by most accounts that foolhardy change cost Altec the studio monitor business :-(
  12. Kyle

    Kyle Junior Member

    The frequency compensation or EQ is similar to the one you have on your crosssovers Bill. You would need to add a section to the N1500 between the the 3uF cap and the tweeter. It would be as shown in red text on this diagram. Please excuse my crappy format, it was the only software I could find this morning.

    Altec used this horn compensation scheme in almost the same values on a variety of different crossovers, including several 604 types and the model 19s. It does not address the peak at 2600 Hz that I have measured on many 802 type compression drivers including the ones on the 604 variants.
  13. Wash&amp;Dry

    Wash&amp;Dry Junior Member

    That's great Kyle! As soon as I figure out how to turn that into a physical crossover I'm going to make it.
  14. rogerfederer

    rogerfederer Junior Member

    bumping this thread as i have some 604Es incoming. gordonw is restoring/reconing them for me... looks like there is not a markwart xover for the 604E and the mastering lab requires bespoke parts. i could build crossovers using the N-1500 schematic and then eq them digitally (will be using with a miniDSP). advice?:smile:
    Audionut likes this.
  15. Read the remarks about the progressive changes in the 604/05s; why they were made and how consumers reacted to the changes:

    marantzfan likes this.
  16. rogerfederer

    rogerfederer Junior Member

    Yeah, interesting!
  17. rogerfederer

    rogerfederer Junior Member

    i also have a thread over on AK. earl k is suggesting i used a modified version of this JE Labs xover for the N-1600:
    "Use the same layout ( as above ) but change the 4uF cap to 3uF.
    Change the 1mH coil to 1.5mH
    Change the 16uF to 14uF
    Keep the rest of the components ( in the above picture ) the same.
    I would use the driver polarities as dictated by the N1500A schematic"

    joseph or joe roberts, you have thoughts?
  18. Hi guys, newish member/forum stalker here. I just saw on the GPA site that they have a 604-8E Alnico that they have just started producing so I guess we need to get these crossovers sorted out!
    marantzfan likes this.
  19. TubeHiFiNut

    TubeHiFiNut Administrator Staff Member

    Welcome to The Haven, @Gibbysmalls :)

    Glad you found your way here. :)

    Please also take a moment to tell us about yourself and your systems in the Introductions and Member Systems room. :)
  20. marantzfan

    marantzfan Administrator Staff Member

    Whoa, no kidding! I just took a peak and it looks like it's already in production and available for purchase. How cool is that, a NEW Alnico 604 Duplex!

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