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Thread: Altec 9844-8B

  1. #91
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    Active?

    Hi guys.

    Skywave. The software is free! Google jdft 2.5. and download the program in 20 seconds. Useful but not too accurate. Then take screen shots with your computer. By the way. If possible use your gears. I bet they are much more accurate than mine. And we need accurate measurement.

    Zilch. Active? I really am thinking about it. Do I have to biamp it? I found out that one of the Marantz side is blown. And lots of cleaning to do. But i am all with you. Let's work on the 806s.

    I have a doctor's appointment today. So, it may be late this evening before I can do anything.

    Tim
    Last edited by MrT; 01-16-2008 at 06:15 AM. Reason: additional comment

  2. #92
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    605s

    Zilch

    By the way. Doesn't 605 use 414 (12inch) bases? My 806a reads 11.8 DCR.

    Tim

  3. #93
    Senior Member hmolwitz's Avatar
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    605

    The 605 is a 15" woofer with a 1" compression driver coaxially mounted.
    The 601 is the 12" woofer, but it has a smaller HF driver the T3000.
    Harry


    http://www.lansingheritage.org/image...pro/page09.jpghttp://www.lansingheritage.org/image...pro/page09.jpg

  4. #94
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by MrT View Post
    Zilch. Active? I really am thinking about it. Do I have to biamp it?
    Yes, of course, but the power requirements of the HF are very modest. They'll even run on wimpy tubes, if you prefer "Organic."

  5. #95
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    Pink Noise 11.2ohm+40.3uf

    Hi guys

    I have a correction to make. I did use pink noise not white. Sorry! And using 11.2ohm and 40.3uf this is the graph I came up with. Again, disclaimer. This is not a fancy or scientific measurement. Don't want to do this to you.

    I can't do active. Need an amp. My Marantz is out! So Zilch I need you to do some magic with 806as.

    Tim
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  6. #96
    RIP 2011 Zilch's Avatar
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    What you had for Zobel was better, looks like.

    This seems to be rolling it off too early.

    I'll try another approach for comparison. Shouldn't have used L1, probably.

    It's instructive, though. Even with rudimentary measurements, it's apparent what's going on.

    Get your HF running. Pull back to 1 M. Let's see how much headroom you have.

    You can swap Zobels in and out while measuring and listening and not harm anything, BTW. The difference should be apparent in both....

  7. #97
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    Listening test

    Hi Zilch

    I realized that in the past few days i've made 3 changes to my Xover. From 3.9mh+8.2uf to 3.5mh+10.5uf, to 3.5mh+10.5uf with 16ohm +8.2uf zobel, and finally 3.5mh+10.5uf with 11.2 ohm+40.3uf zobel. With some alligator clips i listened to three different settings.

    By the way, are you around Berkley area? I used to live in So. Cal for about 10 years or so. And I used to drive up to Berkley area to meet up with my students. Having said that here are my impressions. I can compare the sound of a n800f clone with some what like High Sierras. There are highs and peaks that I can hear . And I can see why some can favor that type of sound. And the last one (the one with 11.2ohm, etc) I can compare with San Luis Obispo. The gentle and rolling hills. Yet, the bass was very clear and well defined. So, I would say 16 ohm+8.2 uf combo is some where in between but it leans towards high sierra side. Hope this make sense. I decided to use these expressions for listening to music and systems can be very subjective. Excellent experience!

    I've been listening to John Lewis "the Bridge Game" vol. 2, Gilels playing Beethoven's Waldstein Sonata, Sychronicity by Police, and Jennifer Warnes' Famous Blue Raincoat.

    Now I am reading David Weems' book.

    So, there you have it.

    Tim

  8. #98
    dlp4341
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    Zilch
    L6 is 5.6 Ohms DCR ( # 28 AWG )
    Your curves look great
    BTW do you have 605As with 8 Ohm woofers
    Don

  9. #99
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    Hi Don, and welcome!

    It's YOUR filter generating the pretty curves; all I did was click some buttons.

    5.6 Ohms makes for a deeper HP notch.

    I was only off by 34%.

    No 605s here at all, alas....

    Why'd you roll it off at 14.5 kHz, Don?

    Looking at the uncompensated response, 806As start taking a dive above there so it becomes a harder push.

    I'm guessing they start sounding nasty if we allow any more boost above there?

  10. #100
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    You found us!

    Hey Don. You found us!

  11. #101
    Senior Member Skywave-Rider's Avatar
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    Quote Originally Posted by Zilch View Post
    At the bottom here is shown a Zobel, which you'll also find discussed in Dickason, used to flatten the reflected impedance of the woofer as illustrated by Earl, above, so that the main filter behaves more predictably.

    Yeah, 6.2 uF for C1 and 4 Ohms for R1s are fine. R2 and the Zobel components vary with the application. You can see that if R2 goes to a high value, providing the minimum of 6 dB compensation, it's basically 8 Ohms in parallel with C1, what I have suggested you try for starters here, as there's already some compensation in N800-F (maybe)....
    I got my contour network parts today. I intend to do the measurements tomorrow. Zilch, since it takes quite a while to mail order components, do you think it's a good idea to order the Zobel parts referred to above? "18 uF and 7.5 Ohms for starters" are what you suggested for dual 16 Ohm 414s.
    Also got Dickason's book, which I have begun reading.

  12. #102
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    Quote Originally Posted by Skywave-Rider View Post
    Also got Dickason's book, which I have begun reading.
    Don't be put off by the math in there, now. It's all rather simple algebra. Go right to the chapter on crossovers for a better understanding of what's going on here.

    Zobels are important primarily for the purpose of making a driver appear more as a resistive load so that the filter(s) behave in a predictable manner. As MrT has just demonstrated, they may also be used to optimize a specific filter/driver combination for a particular performance. However, as you'll see in Dickason, there's often (I'm tempted to say "Always," but I'd probably be wrong,) an equivalent filter design without employing a Zobel, per se.

    Regarding parts, Timbers at JBL is rumored to have a "Crossover Cart" loaded with a selection of components of different values. I kind of have the same, acquired and accumulated over time. I've been wanting to build some switched substitution boxes to make the task easier, and also to prevent me from using my design components in builds.

    So, yes, if you're going to do much of this, it's good to have some parts on hand to plug in and out to observe (and hear) their effect on your design. By your efforts, we'll soon know how well the stock design actually performs, and something more about the limitations of how it may be improved....

  13. #103
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    More Graphs

    Hi Guys

    Here are more graphs. Again, disclaimer. No fancy gears. Just some free program and el cheapo Mic. The Mic was literally right in front of the horn.

    I took out the L-Pads. I realized that I got the wrongs ones. They are 8ohms not 16ohms, all soldered up. So, can't return them. Can I add additional 8ohms to tab 1 and 3and use them as 16ohm pads? Anyways. Here we go!

    Tim
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  14. #104
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    Add 8 Ohms in series with tab 3 only.

    For now, just leave the L-pads out.

    You can see the 806A "Shout" going away there.

    The higher the resistance you put in parallel with the 6 uF now, the more compensation you will get.

    At some point, the woofer will dominate, and you're out of headroom, the difference in sensitivity of the LF vs. HF drivers at the crossover frequency....

  15. #105
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    Is this the end of the road for me?

    Hi Zilch

    Thanks for the reply. I hear you about the headroom. So, am I at the end of the road here? I may be able to pad down the mid more. Then, what happens to the over all balance? Stop now and be happy?

    I would love to see what Skywave will come up with tomorrow just for the learning purpose.

    Over and out for now.

    Tim

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