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Altec 2-way XO update



The Altec N1600C series crossover has been a significant constituent in the evolution of my Altec 2-way horn speaker system. C. G. McProud's 1947 article on page 101 of Audio Anthology, Volume 1, was my first encounter with series crossovers although Western Electric was already using the topology in the 1930s. As an aside, my knowledge of electronics is basic. I don't even own a circuit simulation program and rely on my collection of audio electronic textbooks, old magazines plus what my ears tell me as reliable internet sources for "techie stuff."

JEL/N1600C 2-way Crossover


Based on Earl K's simulations and analysis at the Lansing Heritage forum, Altec configured the N1600C 2-way crossover with staggered filters. In this application, a 2nd order/12dB/octave high pass filter @ ~ 1600 hz is provided by the 4 uf capacitor + 1mH inductor, while the 1mH inductor series connected to a 16 uf capacitor functions as a 1st order/6dB/octave low pass filter @ ~ 1100 hz. The 30 ohm potentiometer is part of an upper midrange frequency attenuator/high frequency EQ boost circuit I derived from reading through Altec 30923 discussions at Audio Karma and at Lansing Heritage. Altec incorporated this circuit in their Model 19 crossover and Jeff Markwart used it in his phase corrected Altec 605 crossover. 

In subjective terms, the combination of staggering the crossover point + upper midrange attenuator creates a "dip" in the crossover region where harshness and congestion can easily be detected by critical listeners, while my Altec 3000H tweeters were made redundant by the high frequency EQ boost.

Outboard crossover built using
paper in oil caps, low DCR air core chokes and
non-inductive resistors


Comments

  1. Hi Joseph,
    Nice amendments to your system.
    Your enthousiasm has resulted in me entering the experimentation path again. I am awaiting a pair of 32 horns to replace my 511b's as we speak.
    Have you ever considered putting the horns inside the 614 'a la Altec 9849?
    Come to think of it, I am running my 614's sans back panel as OB for over 2 years now. Ever tried that?

    Kind regards,
    Ernst
    Edam, city of cheese

    ReplyDelete
    Replies
    1. Hi Ernst,

      I am really enjoying the Altec 2-way with the 32B horns and amended crossover. Based on my research in the internet, the 414A woofer is at its best on an even larger enclosure than a 614. Thus, shoehorning a 32B/802D combo inside will just occupy valuable space.

      Years ago I did try an open back cabinet similar in size to the 614. Here's a picture - http://3.bp.blogspot.com/-TzpJcFdkWPo/Uv77KQ-rsyI/AAAAAAAADV4/9OOrjxxn5pI/s1600/2-way.jpg

      It sounded great in the midrange but I was looking for greater bass extension and dynamics which was provided by the 614. Besides if I needed midrange purity, I always had the OB/755A on standby.

      Thanks for visiting and kep me posted on the 32B!

      JE

      Delete
  2. Hi Joseph,
    I have been fun of your work for years thank you for shearing. It seems to me that your amp designs have 8ohm output transformers and this speaker uses 16ohm drivers. Is it intentional "mismatch" or you are indeed using 160h Ots?

    Thanks,
    Peter

    ReplyDelete
  3. Hi JE-
    I was reviewing your x-over schematic above and notice you have a 2ohm resistor shown. Is that supposed to be a 20 ohm resistor?

    Thanks,
    Dan

    ReplyDelete
    Replies
    1. Yes, those are the values in my present crossover.

      Delete
  4. I have altec 416a speakers with 802d drivers going into 32c horns, in a 612 cabinet. I would like to build the crossover you show here but I am not too knowledgeable about schematics, or how to find paper in oil capacitors like you use here. Can you recommend where to find the types of components you use here?

    Best,

    Jonas

    ReplyDelete
    Replies
    1. If you are based in the USA, I used to gather paper in oil capacitors at hamfests and radio shows. Another source are Russian or Ukranian sellers on eBay. The 1mH inductor, wirewound resistors and 25-30 ohm, 2W pot should be available from Parts Express.

      I hope this helps!

      Delete
  5. Thank you so much. I've finished the crossovers and the speakers. They sound great, but its hard to compare, as I had previously listened to these components in Altec A7 cabinets, with the 511 horn crossed at 500 hz. Very different sound but I think these work better in a smaller room. But I am very happy with your crossovers!
    A few questions. Are your 32b horns plastic, or metal. Mine are the plastic, or possibly fiberglass, 32c unfortunately, and I wonder which ones you think are better. Also, you mentioned in the previous post that you only put damping on two sides of the cabinet. My 612 cabs are insulated on 4 sides, so I was wondering what are the benefits of having only two sides insulated? Lastly, how much higher should I go with the capacitor if I do want a brighter sound. Would a 2uf capacitor be too much of a jump in place of the 1uf capacitor? I'm not saying I need them brighter, but I'd like to try a slightly brighter sound to see how I like it.

    ReplyDelete
    Replies
    1. Mine are plastic also. I've heard the original metal WE32 in a WE753A years ago and it sounded very musical to my ears. But that's a different system context . Since I know I can't afford the metal version, I am happy where I am at now ;)

      Damping two adjacent sides follows the LEDE - Live End/Dead End - principle. Older original Altec cabinets including 614 and 612 I've examined employed this. IME, overdamping well braced cabinets fitted with classic drivers result in dead sound ;(

      I did not experiment extensively with the EQ cap but will suggest +/- .5uf increments.

      Happy Listening!

      Delete
  6. Hello Joseph,

    I've followed your blog for some time now - great work! I've gotten a hold of a pair of Altec 9844 monitors - same components as in your single-driver boxes here (except that the 9844 have two 414z per side). My plan is to house only the two 414z drivers in the original 9844 boxes, oriented vertically with a new baffle, with the horns up top. I'm compensate for the loss of cabinet volume resulting from removing the horn with additional bracing.

    My question is this: do you know if I would I be able to use this crossover schematic as-is on the two 414z + 806a/811b per side arrangement, or would the use of two 414z in parallel on each side (which is how I understand they are wired in the stock configuration) necessitate a change to the crossover?

    As I understand it, you're using the stock n-800f network for the LF (which is what my 9844s use), with the addition of a HF comp circuit.

    I was going to run with your design here as-is, then discovered that not all n-800f networks were the same, so I'm not certain that the base n-800f circuit you're using is identical to the one in my early-ish 9844.

    Conceptually, I haven't been able to grasp how, in the 9844 (and Malibu) two 16 ohm drivers in parallel + 1 16 ohm compression driver results in a speaker Altec rated at 16 ohms.

    Anyway, thanks again for putting your insights on this and other issues here - I've learned a lot.

    The only reason I'm not replicating your project entirely is to save a little $ and use the 9844 cabs. Ultimately, I plan to make two pair of JE Labs-Altec 614 boxes.

    Thanks,

    JB

    ReplyDelete
    Replies
    1. This crossover is based on the Altec N1600C which was used in the 605B Duplex. I am not very familiar with the N800F and would suggest that you stick with that since your driver configuration is different from mine.

      If you want to boost the extreme highs (around 8khz), you can add the 30923 network I linked above.

      Happy listening!

      JE

      Delete
  7. I'm trying to obtain the 30 ohm potentiometer to complete my crossover. They appear to be unobtanium. Unfortunately I don't know enough about how this functions in the series circuit to know whether I can substitute a different value. Can I use a 50 ohm pot? Is the wattage rating also important or can it be higher? Any help would be much appreciated.

    Jeff

    ReplyDelete
    Replies
    1. I've successfully used an 8 or 16 ohm L-pad in place of the 30 ohm pot. Since I only use SE amps, 10-20W rating is plenty.

      JE

      Delete
    2. Thanks, Joseph, for the reply. That helps tremendously.

      Delete
    3. Another question: A friend has obtained 414-8C drivers from GPA and 902-8A horns from another source. Since this is an all 8ohm set of drivers can he use the N-1600C crossover above without modification? If not, any ideas on what would need to be modified in it to work for all 8ohm drivers?

      Delete
    4. Okay that's what I expected - we'd basically need to redesign it for 8 ohm drivers. I'm thinking that's largely because it's a series crossover. We'll give Joe's endorsement a go and see what happens.

      I appreciate the response. Thanks.

      Delete
    5. This XO is specifically for 16 ohm drivers. I've only used this with the older Altec 414A (green) and Z (gold) + 802 with either 20275 or 34852 diaphragms as well as on my Altec 605B (416A + 806 - both 16 ohms). I cannot guarantee it for the newer drivers you mentioned. Adapting the N1600C for 8 ohm drivers is practically redesigning it.

      Edit: Joe Roberts informed me that this is how he runs his 414/802/32 set-up - run the woofer full range. Insert a 1.5uf - 2uf paper in oil cap for the compression driver, no L-pad or EQ/HF peaking circuit. The drivers roll off naturally.

      See his post here - http://audiokarma.org/forums/index.php?threads/dumb-speaker-impedance-question-altec-content.799435/

      Delete

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