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Thread: Altec 9844-8B

  1. #46
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    Quote Originally Posted by Skywave-Rider View Post
    OK, so conduct all the measurements with the N-800-F plus those components? No measurements with N-800-F alone?
    Gotta do both to know what's happening. Again, keep good notes so you can follow it later.

    Quote Originally Posted by Skywave-Rider View Post
    That's 1st order compensation filter, yes?
    Dickason calls it a "Contour network" (Loudspeaker Design Cookbook Fig. 7.155). Operatively, it's a response-shaping step filter. There's a way to make it adjustable, and it becomes the "T-filter" used by Altec in Model 19 and others:

    http://home.earthlink.net/~jmarkwart...1201-8aRev.pdf

    We're setting it to "Max" here, is what....

  2. #47
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    Dickason

    Quote Originally Posted by Zilch View Post
    Dickason calls it a "Contour network" (Loudspeaker Design Cookbook Fig. 7.155).
    OK, I ordered that book and the caps.

  3. #48
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    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)....
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  4. #49
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    Zilch,

    FWIW: The Zobel that's included in Altec(s)' 1209-8a network has these values ;

    R = 7.5 ohms
    C = 18 uF

    <>

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    414z (16ohm) parameter

    Hi Zilch

    I have been following this post and am learning a lot. If you don't mind I will be following this post and have learned a lot. Hey Earl if you responded to the my post at AA, I thank you.

    Question. I found parameter for 414z (16ohm) at DIY which was measured in free air with added mass. Will it be helpful?

    Tim
    Last edited by MrT; 01-12-2008 at 07:12 PM. Reason: mistake

  6. #51
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    Quote Originally Posted by MrT View Post
    Question. I found parameter for 414z (16ohm) at DIY which was measured in free air with added mass. Will it be helpful?
    Yes, of course....

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    Here is the parameter

    Hey Zilch

    I've posted n800f question at the altec sight. Since then, I've been reading 846a/valencia thread. Wow is all I can say.

    Anyways. This is the first time posting up here so let me try here.

    Tim
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    More graphs

    Hey I did it! I got some more! Again, i got these from DIY. The guys there deserve the credit. So here they are.
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    Sorry! An other one here.

    Here comes another one! Zilch. I don't know what these graphs say. I would appreciate your help here. Basically I am trying to clone n800f for 414s and 806as. The one you pointed out to me. Hope I am not hijacking the thread.



    Thanks.

    Tim
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  10. #55
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    Quote Originally Posted by MrT View Post
    Zilch. I don't know what these graphs say. I would appreciate your help here.
    First one is impedance and phase, basically confirming the one Earl posted earlier. The impedance is substantially on the rise between 200 Hz and 2 kHz, the area of interest. Note the glitches ~2 Hz, common to both curves, independently measured. Something's up with those drivers at that frequency. The T/S parameters derived from that curve appear at the bottom there.

    The next one is a software analysis of a two-way crossover, but it seems not to be the stock N800-F, as, while there is a spread between the low and high pass filters (782 Hz - 1028 Hz,) that is not as wide as I believe it to actually be. Also, the Altec filters are not Butterworth. I've never measured the voltage drives, but I suppose I could do that for some N800-8K clones I recently built. For now, I'll take a look at my sims to see if that's how N800-F behaves with the "wrong" impedance drivers.

    Last one is an RTA plot of the woofer, but not taken nearfield, apparently, and in an unknown alignment. Thus, it's only the higher frequencies which are reliable, and we can see that the driver's natural roll-off occurs well above the crossover region under consideration here. The response appears relatively flat from 100 Hz to 3 kHz....


    Edit: N800-F looks like it could work, actually. Here are the simulations of the voltage drives, assuming resistive loads. Green and Yellow are 16-Ohms Cyan and Violet are with 8-Ohm loads. Red marker "a" is at 1.2 kHz, and there's 13 dB of HF compensation using 8 Ohms at that point. I suspect the acoustic crossover point may be somewhat lower than that, in which case 902-8As will likely be running out of headroom against dual 414s. Skywave's going to show us how it actually performs....
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    RTA Plot

    Hey Zilch

    Thanks for the analysis. I understand it better now. I know the RTA plot was done with the driver in a 120lt cab. The guy who provided the parameter xoed his at 1200hz. However, I did not understand how the value of these component correlates 3.9mh+8.2uf. Second order butterworth? I thought the crossover was some what close to n800f. It will be great to see skywave's findings.


    Tim
    Last edited by MrT; 01-13-2008 at 07:04 AM. Reason: misspell

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    Filter Question

    Hi Zilch and Earl

    I've been reading that Valencia thread over and over again. Now, I have a little better understanding of what filters are for. It took a long time and reading to understand the filter concept. While we are waiting for the Skywave's results I would like to ask some questions. The compensation filters you design: http://audioheritage.org/vbulletin/s...329#post160329 Was it for bms drivers or can it be used for 806as without any modification in addition to n800f? If I were to copy m19's crossover, or do i need to if I follow your filter, what changes do I need to make for my drivers are 16 ohms. I bought my drivers in December. And I want to enjoy them as long as I can.

    Your suggestion for the active crossover sounds very attractive. i have to pull out my old Marantz and start cleaning it up. But this has to be long term project.

    Thank you.

    Tim

  13. #58
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    It's for BMS drivers. Wait for the outcome of these evaluations, or move up your priorities to go active.

    M19 is for 8-Ohm drivers. What crossovers are you using now, N800-F? If so, build the "T-filter" and add it between your crossovers and drivers. Start with no R2, as we are doing here. That'll give you 3 dB more compensation than is built into N800-F.

    Unless you go active, you're going to run into the headroom problem with less compensation, even, as 806As are 3 dB less sensitive than 802/902.

    In either case, you're not going to get as much HF extension as the Altecs with the Tangerine phase plug. Those curves are in the Valencia thread. If you decide to change diaphragms to eek out the max you can, go with the Radians, perhaps. I tested those there, also, but not in 806As.

    We don't yet know how the N800-F is going to work with 414s. I like the LF rolloff I see in the sims, but only the measurements can tell us what the result is, acoustically, once that voltage drive is combined with the frequency response of the paired drivers....

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    compensation

    Hi Zilch

    Thanks for the reply. I have not finalized my crossover yet. I got my 806s a month ago and 414 3 weeks ago as Christmas present. And, I am using a temporary mean to get by for a while. After reading your valencia thread at least 3 times, I decided to go with n800f clone for sure. I think holding onto 806 may be purely emotional for BMS looked real good. So.... I feel terrible for saying this. I am already thinking about buying new drivers.

    But for now, after looking at Skywave's results I will add t filters and zobel accordingly.

    Thanks

    Tim

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    Hijack / Hijack !

    - Donaldpatton has done as much as can be accomplished to lift the HF response of the ( anemic ) 806a .
    - He's presented the best ideas that I've seen ( to date ) for bringing the 806 into the 21st century.
    ( Of course Zilch might just junk this driver and encourage the purchase of a BMS / based strictly on FR response plots - that's hard to argue against )

    - Donalds' excellent work can be seen Here ! ( at his website )



    Highlights ( in the Hipass circuit ):

    - The resonant LCR circuit ( in the HF bypass part of the citcuit ) that's centered around 14K can provide an actual "boost" for frequencies beyond 10K ( where the 806 takes a HF dive ) . This approach is the only way to go when trying to get the last few db(s) of HF from the 806 ( & old 802 variants ).

    - The LCR notch filter ( trap ) centered on the drivers fundamental resonance is another highlight that I like .

    - I appreciate the fact that this is a single pole ( 6 db ) hipass / summing with an 8 pole Bessel lowpass .

    Changes ( I'd make / & these are really personal preference ) :

    - I'd explore losing the padded "drive" pots arrangement ( R2 ,R3, R4 & R6 ) . I'd redesign the padding arrangement to instead use a "T" type pad ( variable or fixed ) . This should offer a more "constant impedance" for the main filtering cap . Of course this would mean the HF contour circuit would need to be attached at either end of the "T" pad and the LC values altered accordingly for the new impedancce .
    - I might add a coil ( a second pole ) for an 811 horn-driver combo / if the FR warrants the extra filtering . I'd likely place this coil "after" the "T-Pad" ( to take advantage of the lower working impadance in this area of the hipass / hence a smaller / cheaper part ) .



    ps ; Gone till the weekend ( so, no more posting by me / I'm hoping Zilch will take the bait and run with it )

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