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Thread: Think We May Have a Keeper Here!!!

  1. #91
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    "Okay, my best guess ( for Tues. ) is that the "tight-pack" layout of Todds' construction is forcing the .8mH coil into being a larger "virtual" value. I'll have to try some parts substitutions ( Wed. ) to see what value coil would cause this lower reading in F3 . ( Coils interact with other coils when placed in close proximity )

    - In the meantime Zilch, you should verify Todds F3 numbers ."

    Yes Zilch, if you can, please do. My equipment here is less than steller.

    "Once finished ; lift the .8 mH coil from its' present location / extend with 12" of wire on either end of the coil/ replace the "new coil" into the circuit & remeasure the horns' F3 for its' high-pass ."

    Earl, this is no easy task as the coils are glued in place.

    "- A couple of notes ; the .6 mH coil in the 3105 omits the use of both 20 ohm load resistors ( compared to the 3106 ) . Todds use of .5 mH coils begs the question ; "What about the usage of load resistors ? Impedance plots should be run with & without the resistors inplace . Then full voltage runs should be worked-up for each scenario so one can study the consequences of ad hac parts substitution ."

    I think that the 20 ohm resistors may have been a later addition after the 3105 specs were published (continued on-going development/specifications subject to change). Even Zilch's N200B has them and they are not included in that schematic either.

    "- My opinion, on the whole is pretty well beside the point / except to say / both Todds' and your declarations, that this "workedup design" is a done deal and ready to implement ,,, is vastly overstated - to put it mildly."

    I've never said it was a "done deal" and sent the crossover to Zilch to see if it could be improved (especially in the 500-800 Hz area).

    "- A study of the actual derived "acoustic" slopes is enlightening ."

    Agreed.

    regards

  2. #92
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    Earl, as I noted, one possibility is that my function generator is off and I said I would check it against my digital keyboard.

    I think that your measurement is valid and these do crossover close to 800 Hz as they are supposed to. When I play an A880 on the keyboard and listen to the "beat frequency", the function generator shows this to be at about 750 Hz on it's dial. So the display on the generator is at least 100 Hz low in this range.

    I guess I'll have to find a way to recalibrate the function generator using the keyboard as a reference.

    Quote Originally Posted by Earl K
    - Okay, my best guess ( for Tues. ) is that the "tight-pack" layout of Todds' construction is forcing the .8mH coil into being a larger "virtual" value. I'll have to try some parts substitutions ( Wed. ) to see what value coil would cause this lower reading in F3 . ( Coils interact with other coils when placed in close proximity )


    - In the meantime Zilch, you should verify Todds F3 numbers . Once finished ; lift the .8 mH coil from its' present location / extend with 12" of wire on either end of the coil/ replace the "new coil" into the circuit & remeasure the horns' F3 for its' high-pass .


    - A couple of notes ; the .6 mH coil in the 3105 omits the use of both 20 ohm load resistors ( compared to the 3106 ) . Todds use of .5 mH coils begs the question ; "What about the usage of load resistors ? Impedance plots should be run with & without the resistors inplace . Then full voltage runs should be worked-up for each scenario so one can study the consequences of ad hac parts substitution .



    - My opinion, on the whole is pretty well beside the point / except to say / both Todds' and your declarations, that this "workedup design" is a done deal and ready to implement ,,, is vastly overstated - to put it mildly.



    - A study of the actual derived "acoustic" slopes is enlightening .

    regards

  3. #93
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    Comparative listening:

    I compared Todd's crossover to 3110/3105 using "Big Boy" drivers (2446J) and 2380A horns, 2407H tweeters on PT-F95 to match.

    Had to pad down the 3110/3105 midrange output 6 dB to achieve balance with 2235H woofer, as frequently before, with mid control set to "Min."

    Voicing is remarkably similar; I get strong imaging.

    Todd's crossover is perceptibly cleaner sounding. It'd take Mr. "Golden Ear" Widget to be more definitive, probably.

    I find myself wishing I had damped diaphragms to try. N/A in 16 Ohms, looks like, unless that'd be 2451SLJ?

    Also now see y'all made a little "To do" list for me.

    [I'll figure it out over dinner; still listening: "Migration"....]
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  4. #94
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    SIM with MF L-Pad set -6 dB, HF wide open, then actuals from system above:

    LF taken 12" nearfield.

    MF SIM HP -3 dB = 877.5 Hz per cursors.
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  5. #95
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    Hi Zilch

    Some Observations ;

    - What are the loads ? Are they dummy resistors or the actual transducers ?
    - It's hard to actually read this plot .
    - I'd suggest using a linear scale in the horizontal ( frequency axis ) .
    - If continuing to use a log scale , then 10 hz to 100 hz to 1000 hz and so on , is more the norm .

    More Observations on the Band-Pass Circuit ;

    - The F3 , in the horns' hipass reads to me as @ 540 hz ( ??? ) . I just don't understand the cursors declaration of a 877.5 hz point . That seems to be some sort of anticipated Fx point or a point in a specified "XY" window where the woofers curve crosses a 3 db down point .

    More Observations on the Woofer Circuit ;

    - The electrical F3 , for the woofers' low pass appears to read; 360 hz . I doubt that is right / so I'm confused .

    In Closing ;

    - Is it only my eyes / giving me these numbers ?
    - All in all, this plot creates more questions in my mind than it answers .
    - I'd like to hear from others as to what they get from this FR plot .



  6. #96
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    Quote Originally Posted by Earl K
    What are the loads ? Are they dummy resistors or the actual transducers?
    The black SIM plot uses dummy resistors, nominal, at 8, 16 and 8 Ohms, respectively. If I use the actual impedances, nothing changes much.

    The RTA plots are the actual sonic performance of the drivers connected to the crossover, with dummy loads on the sections not illustrated in each, 8, 15, and 8 Ohms. These illustrate the resultant acoustic slopes of each section.

    The SIM scale is set to match the RTA scale, and the RTA plots enlarged so you can see how they relate graphically. It's easy. Think "200, 400, 600," etc.

    It appears to me that it's all behaving according to design. The woofer rolloff is making the acoustic LF LP steeper than the electrical slope illustrated, matching the MF HP's 18 dB/octave slope. The acoustic crossover point is therefore somewhat lower. Cool.

    Quote Originally Posted by Eark K
    The F3 , in the horns' hipass reads to me as @ 540 hz ( ??? ) . I just don't understand the cursors declaration of a 877.5 hz point . That seems to be some sort of anticipated Fx point or a point in a specified "XY" window where the woofers curve crosses a 3 db down point .
    You guys are measuring the F3 down point of the MF HP. I set cursor (a) to show what the SIM says it is (c,d). That does not vary with attenuation, but the "crossover point" does, of course.

    Cursor (b) shows the M/H crossover point with L3,4 at 3105's 0.6 mH being 6.581 kHz with no UHF attenuation. That point shifts as the balance between MF and UHF is altered, one argument in favor of cascading: it holds that point stable when LF/HF balance is adjusted. It's easily seen that attenuating the UHF raises the MF/UHF crossover frequency as it "slides" down the MF LP slope.

    Quote Originally Posted by Earl K
    The electrical F3 , for the woofers' low pass appears to read; 360 hz . I doubt that is right / so I'm confused.
    No, the curve is correct. See Giskard's earlier SIM of the N200B here:

    http://audioheritage.org/vbulletin/s...0&postcount=41

    That particular part can be tweaked with the Zobel, if desired.

    For better or worse, it's one reason we have confidence in this design: It's assembled from production models using similar drivers....

  7. #97
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    Quote Originally Posted by Zilch

    - The sim scale is set to match the RTA scale so you can see how they relate graphically. It's easy. Think "200, 400, 600," etc.
    Ahh, okay ! Thanks for that explanation .

    - Why didn't you test the actual network , as contructed by Todd ? We'd all like to know the actual F3 points that he has achieved with real loads .

    - Since this is a "SIM" of an actual physical network , could you please post a "screen-capture" of your softwares' data-entry page ? This will show the components ( with values ) that were used to create the "black sim plot".

    - This way, we will know what band-pass configuration you are using for the components . ( Moving the LC components one side or the other of the circuits' Lpads does change the crossover points ) . The last orientation I saw was the cascading type with the LC elements, driver-side of the 16 ohm variable Lpad .

    Thanks !




    Quote Originally Posted by Earl K

    - Originally Posted by Earl K
    The electrical F3 , for the woofers' low pass appears to read; 360 hz . I doubt that is right / so I'm confused.
    Quote Originally Posted by Zilch
    No, that is right. See Giskard's sim of the N200B here:
    - Wouldn't the F3 points be closer to 560 hz , considering the horizontal scale that's in use for both Giskards' and your just published sim ?



  8. #98
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    Quote Originally Posted by Earl K
    Since this is a "SIM" of an actual physical network , could you please post a "screen-capture" of your softwares' data-entry page ? This will show the components ( with values ) that were used to create the "black sim plot".
    It's per the construction schematic, above, i.e., cascade, with the MF HP after the L-Pad.

    I'm reluctant to post the input schematic as it incorporates additional components to properly model the inductors, and fixed resistors in lieu of L-Pads, serving largely to confuse those who might want to build these.

    So, if you'd PM me your eMail address, I'll be happy to send it along to you....

    Quote Originally Posted by Earl K
    ( Moving the LC components one side or the other of the circuits' Lpads does change the crossover points.)
    Yes, and we don't have the autotransformer helping us out with that.

    Quote Originally Posted by Earl K
    Why didn't you test the actual network , as contructed by Todd ? We'd all like to know the actual F3 points that he has achieved with real loads.
    Yeah, I can do that, as well. Just gotta rig up an attenuated and isolated XLR input cable. I'll try to get that together this evening....

    Quote Originally Posted by Earl K
    Wouldn't the F3 points be closer to 560 hz , considering the horizontal scale that's in use for both Giskards' and your just published sim ?
    Yes. It's certainly not 360 Hz.

    [But, it's not 800 Hz, either.... ]

  9. #99
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    I assume that like me, you are using silver solder exclusively.


    Quote Originally Posted by Zilch
    It's per the construction schematic, above, i.e., cascade, with the MF HP after the L-Pad.

    I'm reluctant to post the input schematic as it incorporates additional components to properly model the inductors, and fixed resistors in lieu of L-Pads, serving largely to confuse those who might want to build these.

    So, if you'd PM me your eMail address, I'll be happy to send it along to you....

    Yeah, I can do that, as well. Just gotta rig up an attenuated and isolated XLR input cable. I'll try to get that together this evening....

  10. #100
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    Quote Originally Posted by toddalin
    I assume that like me, you are using silver solder exclusively.

    Pfffttt!!!



    [At least it says "Rosin Core."]



    Two full system adjustment curves:
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  11. #101
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    Quote Originally Posted by Zilch
    - I'm reluctant to post the input schematic as it incorporates additional components to properly model the inductors, and fixed resistors in lieu of L-Pads, serving largely to confuse those who might want to build these.
    - Don't be shy ,,, publish it .

    - To address the concerns of the easily confused, dump it into a photo editor like "Paint-Box" . Then paint big red circles around those areas of parts' that represent substitutions or a deviation from the preferred circuit ( ie; in the case of the variable Lpads ).




  12. #102
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    Voltage Drive Curves

    All drivers connected and running

    Low res = 5 dB/dotted line:

    [Reposting the SIM so y'all don't have to scroll....]
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  13. #103
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    Voltage Drives Cont'd

    Hi res = 2.5 dB/dotted line:
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  14. #104
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    Well, lookie there!

    All working according to design, apparently.

    -6 dB at 800 Hz and 6 kHz, looks like....

    Unless somebody needs something else quickly, I'm sending it back to Todd today.

    I'll build up a pair to investigate optimum UHF configuration further....

  15. #105
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    What's going on here?

    Three approaches to analyzing the crossover are shown above:

    1) SIM (the black plot) is the theoretical performance. The circuit and component values are entered into a Spice simulation program which "runs" it in a mathematical model to display what it does.

    2) RTA uses a microphone to "listen" to the actual performance and show it. Run each driver on the crossover individually with appropriate value resistors in place of the other drivers as "dummy" loads. There's an entire literature on getting accurate RTA (and other) measurements of loudspeaker performance.

    3) "Voltage Drive" uses RTA as display device, but in place of the microphone, the actual crossover outputs (with all of the drivers connected and running) are each used as input. As with RTA, I'm using pink noise is the program source, attenuation as required, and an input isolation transformer to protect the RTA. White noise and sinusoidal sweep are additional source options.

    Taken together, the three approaches provide means to assess crossover performance: Is it working according to design? Is the design appropriate for the task? Is it optimum for these drivers in this alignment?

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