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Thread: Altec 9844-8B

  1. #316
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    Quote Originally Posted by Skywave-Rider
    Earl, are you saying I should re-measure the 902s with the loading caps back on? I think I kept them.
    - I haven't done any work with my 902s so I don't know how linear I can get their response ( with or without the loading caps ) .
    - Give it a go ( measure, add the loading caps, & then remeasure ) / I just wouldn't expect miracles .
    - Conversely, I've demonstrated that 802s ( with either type of phase plug ) can give very linear response ( on non-Altec, older-style horns ) .
    - The 802s have guide pins for the diaphragms making a fit-up a one-shot deal ( unlike the 902s ) .
    - If I had Altec drivers on 811b horns , I'd be looking to reduce their roller-coaster response as well as reducing the inherent coloration .

    - Below ( on the left ) is a CSD sonogram ( from Zilch ) of your 902 on the 811b horn . This CSD is normalized and ( IMO ) quite clearly shows the horns' inherent coloration's are just 10 db below the fundamental frequencies .
    - Since I like radial horns,( & if I had a pair of 811s ), I'd be working at reducing those coloration's into the more typical sub 20 db range .

    - The work done by Urei back in the late 1970s can be used a starting point in the practice of adding different types of foam to the interior surfaces of horns / when wanting to affect the frequency response .


    <> cheers EarlK

    ps ; One could see if they could get the CSD colorations down to a level such as I've shown on the right hand CSD ( this is an Altec 802-8T on a Sammi BiRadial , normalized quite flat with passive EQ ) .
    .

  2. #317
    Senior Member Skywave-Rider's Avatar
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    Earl,
    I've been meaning to get some open cell foam a la Geddes and stuff it between the vanes to hear what happens.

    When I get the loading caps back on I'll re-measure with better tools than I had earlier in the thread.

  3. #318
    Senior Member Skywave-Rider's Avatar
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    Farewell, friend.


  4. #319
    Senior Member Russellc's Avatar
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    What can one say....

    Quote Originally Posted by Skywave-Rider View Post
    A terrible sad blow to DIYers everywhere.

    Thanks here too Zilch, you are missed...no one to field my really tough questions on 2 ways.

    Russellc

  5. #320
    Senior Member Doc Mark's Avatar
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    Good Evening, All,

    This sad news is something I'd not heard, and I'm very sorry to have heard it today. I never got to meet him, but Zilch was one of a kind, in many ways, and his passing will leave a huge hole for those that love their Legacy speaker systems. May he find peace, comfort, and happiness, and may his family do likewise. Thanks to all who have passed along the situation, and my Zilch rest in eternal peace. God Bless him, and all others like him.

    Sadly,
    Doc Mark
    The only thing that can never be taken away from you, is your honor. Cherish it, in yourself, and in others.

  6. #321
    Senior Member Skywave-Rider's Avatar
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    A long time ago Zilch suggested I combine the low pass from the N800F with the high pass of the Z19.
    So I did, finally, substituting the 2.7 mH coil with a 3.5 mH. The 21 uF cap is now a 10.5 uF (approximately.)
    Sounds very good. But I have to roll them out of my office and into a bigger room when available. At that time I’ll measure the hybrid and give a better listen.

  7. #322
    Senior Member Skywave-Rider's Avatar
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    Some preliminary FR measurements here.

  8. #323
    Senior Member Skywave-Rider's Avatar
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    I finally tweaked the measurements to gate out the floorbounce, anechoic down to 340Hz:

    1. 9844 with active crossover, Altec 902 (RED) vs. BMS 4552ND
    2. 9844 with 902 driver on Z19N passive crossover (Z19 with N800F low pass) showing woofer/tweeter and full range
    3. 9844 with BMS 4552 on Z19N passive crossover (Z19 with N800F low pass)
    4. 9844 on its side with 511 horn on top/902/active
    Attached Images Attached Images     

  9. #324
    Senior Member JoMoCo's Avatar
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    Hey Sky, so both the red & blue are on the original 811? Does your 902 have the back removed or still on?

  10. #325
    Senior Member Skywave-Rider's Avatar
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    Quote Originally Posted by JoMoCo View Post
    Hey Sky, so both the red & blue are on the original 811? Does your 902 have the back removed or still on?
    Yes, both on the 811 in the cabinet. The 902 backs are the larger type, with felt, not the loading caps. I think I still have the loading caps somewhere.

  11. #326
    Senior Member Skywave-Rider's Avatar
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    902 & QSC with and without loading cap

    I promised to do this a while ago. This is a 902 driver on QSC HPR 152i waveguide with loading cap (orange) and without (green.) Same driver. Crossover is 4 Pi.

    Red is DE250 on same setup.

    Name:  902:QSC w:w-o loading cap.png
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  12. #327
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    Please, help with T-Filter

    Quote Originally Posted by Zilch View Post
    Here's the "T-filter" standing alone, top. Altec used it to provide supplemental HF compensation after some stock crossovers.

    As you see in the M19 crossover, R2 may be varied to adjust the amount of compensation.

    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)....

    Thank you for your posts related to this area of the Model 19 crossover. I have been trying to sort out the T-Filter and how it affects the high freq response.

    I, too, am trying to 'clone' this crossover and use it for my own system.

    The attenuation of my HF driver is fixed, however, not with using L-Pad potentiometer.

    This crossover's use of potentiometers and T-Filters? or Step-Filter? confuses me.

    I am familiar with L-Pads or attenuation circuits but have not seen this topology for potentiometers.

    How does the T filter functions here?

    How does it affect the high frequency response?

    I would like to boost the highest frequencies 4-20k and/or reduce the 'Shouty' mids 700-2k.

    Is the T-filter simply wired as shown in the diagram?

    I have loads of resistors - no pun intended - so I thought I would do some experimenting with it.


    The driver I am using is an EV DH1 with FaiTal LTH142 Elliptical Tractrix lens: http://www.faitalpro.com/en/products...p?id=903020105


    Thanks again for all the help.




    <DIV align=center>
    <img src="http://usr.audioasylum.com/images/5/54573/altec_30904-30923_attenuator_equalizer_circuit.jpg">
    </DIV>
    <DIV align=center>
    <img src="http://usr.audioasylum.com/images/5/54573/faital-pro-hf146-f-size475.gif">
    </DIV>

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