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

  1. #1
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    Think We May Have a Keeper Here!!!

    After many hours of playing/experimenting with the crossover (including such things as by-assing the choke, caps, etc.), I think I have achieved a level of success! Bands indicate a change of 2 dB.

    Note the included 10-band spectrum analysis (band on far right is volume). Sorry about the poor contrast, but you get the idea. BTW, the ultimate solution was to place 16 ohms in series with the woofer that flattened the 63-250 bands while leaving the 500 Hz band fairly intact.

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    1) You should not have to attenuate the LF driver. If it's playing too loud in relation to the mid and high, that'd be because THEY are over-attenuated, most likely. There's plenty of headroom between the efficiencies of the LF versus M/H drivers. Something else is up.

    2) You certainly don't want to attenuate the LF with series resistance, which will a) mess up the filter frequency and b) preclude the amplifier damping woofer cone movement.

    3) Bypassing the LF filter is a bad approach. You end up with the woofer playing well into the MF range, with all of the concomitant phase interaction between drivers. I'm not able to analyze the full consequences of your unorthodox use of an L-Pad there. Having the full schematic would be helpful.

    4) You know from your near-field LF measurements that the RTA is not seeing what's actually happening at the low end. Measure your LF separately to verify there's nothing anomalous going on, and then rely upon it's performance near the 800 Hz crossover range on the RTA to establish the balance. Ignore what the RTA says below that.

    5) In my experience, this MUST all be done "By the book" to succeed. All of the requisite capability is already built into the crossover to accomplish the task.

    6) If it sounds good without messing around with the LF, and you are confident it's working according to design, just leave it be as designed. You may be attributing more to the RTA analysis than is warranted.

    7) Alternatively, send me one of the crossovers, and the schematic "as built." I'll break out an LE175 and 2402 here to run with 2235H and test/troubleshoot it....

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    Thanks, to enlighten me, and possibly others on this forum, can we take these points one by one???

    Quote Originally Posted by Zilch
    1) You should not have to attenuate the LF driver. If it's playing too loud in relation to the mid and high, that'd be because THEY are over-attenuated, most likely. There's plenty of headroom between the efficiencies of the LF versus M/H drivers. Something else is up.

    While the horn can play louder than need be, the tweeter at full out is a hair down from the woofer (with the addition of a 1 mfd that was subsecquently added). However, some attenuation of the woofer results in a far smoother overall curve.

    2) You certainly don't want to attenuate the LF with series resistance, which will a) mess up the filter frequency and b) preclude the amplifier damping woofer cone movement.

    Mess up the filter frequency! Yes, this is what is producing a nice flat woofer response as opposed to a dip at 500 Hz without the attenuation. So if messing it up improves it, is that really messing it up???


    3) Bypassing the LF filter is a bad approach. You end up with the woofer playing well into the MF range, with all of the concomitant phase interaction between drivers. I'm not able to analyze the full consequences of your unorthodox use of an L-Pad there. Having the full schematic would be helpful.

    A bad approach??? I can't tell you how many JBL schematics I perused that use this approach. It also fills in the 500 Hz dip. So is smoothing the response a bad thing???


    4) You know from your near-field LF measurements that the RTA is not seeing what's actually happening at the low end. Measure your LF separately to verify there's nothing anomalous going on, and then rely upon it's performance near the 800 Hz crossover range on the RTA to establish the balance. Ignore what the RTA says below that.

    I'm not really concerned about what's happening at the low end and recognize that this is largely a function of room acoustics. My concern lies between the 500-1,000 Hz range. Unforetunalely with an octave eq and reads at 500 and 1,000, it's hard to get an accurate view of what's going on at 800 Hz.

    5) In my experience, this MUST all be done "By the book" to succeed. All of the requisite capability is already built into the crossover to accomplish the task.

    6) If it sounds good without messing around with the LF, and you are confident it's working according to design, just leave it be as designed. You may be attributing more to the RTA analysis than warranted.

    Possibly, but my my ear is sensitive to the 500 Hz range for vocal intelligability. When I set it to run flat (with the 16 ohms on the woofer), there is no denying that the vocals become more pronouced and words become more intelligable.

    7) Alternatively, send me one of the crossovers, and the schematic "as built." I'll break out an LE175 and 2402 here to run with 2235H and test/troubleshoot it....
    Thanks for the offer.

    Contrast these two spectra. The first is the crossover per the JBL L200B/N7000-8000 schematic. In this view, the 1.0 mfd cap has been removed from the tweeter (still the internal 1.5 mfd and choke per the N7000/N8000) to raise it's volume to better match the woofer. The horn is running at near full capacity. I could bump it a little more creating a broad peak at 2-4K Hz.





    This second spectrum has a 16 ohm resistor between the woofer and crossover output. Also based on the decreased volume, I can place the 1.0 mfd cap on the tweeter better tailoring its response.


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    1) You should not have to attenuate the LF driver. If it's playing too loud in relation to the mid and high, that'd be because THEY are over-attenuated, most likely. There's plenty of headroom between the efficiencies of the LF versus M/H drivers. Something else is up.

    While the horn can play louder than need be, the tweeter at full out is a hair down from the woofer (with the addition of a 1 mfd that was subsecquently added). However, some attenuation of the woofer results in a far smoother overall curve.

    2402 is 110 dB, 2235 is 93 dB. Something is up in the UHF? Again, we need the schematic. I recall you did not cascade the MF/UHF, which should have provided even more drive to the UHF.


    2) You certainly don't want to attenuate the LF with series resistance, which will a) mess up the filter frequency and b) preclude the amplifier damping woofer cone movement.

    Mess up the filter frequency! Yes, this is what is producing a nice flat woofer response as opposed to a dip at 500 Hz without the attenuation. So if messing it up improves it, is that really messing it up???

    It messes it up in other ways. If it's TRULY down at 500 Hz, and you need to do your near-field measurements to verify that, then the LF should be modified in other ways to correct it. I doubt your 2235's are behaving like that; I'm bettin' room stuff. Turn off the MF and HF and put the RTA mic about 6" away from the 2235 dome center. What's that look like?


    3) Bypassing the LF filter is a bad approach. You end up with the woofer playing well into the MF range, with all of the concomitant phase interaction between drivers. I'm not able to analyze the full consequences of your unorthodox use of an L-Pad there. Having the full schematic would be helpful.

    A bad approach??? I can't tell you how many JBL schematics I perused that use this approach. It also fills in the 500 Hz dip. So is smoothing the response a bad thing???

    Smoothing the response is not a bad thing, but letting the LF play into the MF certainly is. We're not talkin' SR or bookshelf crossover here. If the LP slope or frequency needs adjusting to smooth the response, that can be done.


    4) You know from your near-field LF measurements that the RTA is not seeing what's actually happening at the low end. Measure your LF separately to verify there's nothing anomalous going on, and then rely upon it's performance near the 800 Hz crossover range on the RTA to establish the balance. Ignore what the RTA says below that.

    I'm not really concerned about what's happening at the low end and recognize that this is largely a function of room acoustics. My concern lies between the 500-1,000 Hz range. Unforetunalely with an octave eq and reads at 500 and 1,000, it's hard to get an accurate view of what's going on at 800 Hz.

    Use your SPL meter near field for the detail.


    5) In my experience, this MUST all be done "By the book" to succeed. All of the requisite capability is already built into the crossover to accomplish the task.

    Reiterated above....


    6) If it sounds good without messing around with the LF, and you are confident it's working according to design, just leave it be as designed. You may be attributing more to the RTA analysis than warranted.

    Possibly, but my my ear is sensitive to the 500 Hz range for vocal intelligability. When I set it to run flat (with the 16 ohms on the woofer), there is no denying that the vocals become more pronouced and words become more intelligable.

    You know what you hear, of course. The L-Pad connection you described above is not 16 Ohms in series with the woofer. If 500 Hz is the frequency at issue, that has nothing to do with the MF or HF. Turn them off and see what's up.


    7) Alternatively, send me one of the crossovers, and the schematic "as built." I'll break out an LE175 and 2402 here to run with 2235H and test/troubleshoot it....

    Thanks for the offer.

    I'll measure 2235 in L200 here. Give me 15 minutes to post it for comparison....

    Edit: Near field, 4". There's a 5 dB notch at 500 Hz, a 2 dB peak at 710, and an 8 dB notch at 900 Hz. It's not the crossover. I'm guessin' it's the 4" cabinet lips all around. I'll confirm looking at the other one after dinner....

    Re-Edit: Second unit similar (bottom), too much so at the same frequencies for it to be coincidence. I'm now doubting it's the room at 4", but will try a different room tomorrow.

    Who else here has RTA and 2235H in L200's?

    Reviewing your spectra, maybe dial the MF back to achieve a balance between the LF and UHF instead of trying to bump them both up to match the MF. How well does that work?

    450 Hz. is ~30" wavelength.

    450, 900, 1350, 1800....
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  6. #6
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    Quote Originally Posted by Zilch
    1
    You know what you hear, of course. The L-Pad connection you described above is not 16 Ohms in series with the woofer.

    Actually it is. I tried two 8.2 ohm resistors in series AND I measured the resistance of the L-pad once getting the freq flat.


    I'll measure 2235 in L200 here. Give me 15 minutes to post it for comparison....

    Edit: Near field, 4". There's a 5 dB notch at 500 Hz, a 2 dB peak at 710, and an 8 dB notch at 900 Hz. It's not the crossover. I'm guessin' it's the 4" cabinet lips all around. I'll confirm looking at the other one after dinner....

    Re-Edit: Second unit similar (bottom), too much so at the same frequencies for it to be coincidence. I'm now doubting it's the room at 4", but will try a different room tomorrow.


    Who else here has RTA and 2235H in L200's?

    Reviewing your spectra, maybe dial the MF back to achieve a balance between the LF and UHF instead of trying to bump them both up to match the MF. How well does that work?

    450 Hz. is ~30" wavelength.

    450, 900, 1350, 1800....

    "You know what you hear, of course. The L-Pad connection you described above is not 16 Ohms in series with the woofer."

    Actually it is. I tried two 8.2 ohm resistors in series AND I measured the resistance of the L-pad once getting the freq flat.

    Edit: Near field, 4". There's a 5 dB notch at 500 Hz, a 2 dB peak at 710, and an 8 dB notch at 900 Hz. It's not the crossover. I'm guessin' it's the 4" cabinet lips all around. I'll confirm looking at the other one after dinner....

    Re-Edit: Second unit similar (bottom), too much so at the same frequencies for it to be coincidence. I'm now doubting it's the room at 4", but will try a different room tomorrow.

    Thanks, at least I know I'm not crazy and my analyzer is fairly accurate in that range. Doesn't my testing demonstrate that it is possible to get rid of the 500 Hz notch, perhaps at the expense of ??? However, with proper crossover design/implementation the notch could be removed without too many other repercussions?

    As to the tweeter being much louder than the woofer, I think the poor quality of the included microphone with the analyzer is rolling off the high end response so that there are really more highs than shown on the analyzer. When I get the highs flat, my Yamaha RX-Z9 goes through and reduces them when it goes through autoeq. Will continue to experiment/measure and will get a schematic posted.

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    WE ????

    - I'd love to see a schematic for your final setup .
    - I'd also like to see the impedance response for this network .
    - I'd also like to know the insertian loss for this network ( it would appear to be quite high ) .

    - From what I can glean from the initial descriptions ( and if I understood correct ) , it appears the woofer & horn drivers' voice coils ( maybe tweeter ) are arranged in a parallel/series topography / all the while, sharing a common earth through a fixed path to earth ( 20ohm conjugate on driver ) as well as the variable resistance represented by the Lpads' shunt path to ground ( variable R existing across, pin 2 to 1 ) . The series arrangement comes into this because ( at least ? ) 2 voice coils are tied together ( in series ) by that central terminal (#2 ) of the horns' variable LPad and the 20 ohm comp driver conjugate .
    - The paralleled inductor across the horn driver line represents one element necessary ( to be kept "in place" ), to help keep this quasi "Series" network from cooking the HF drivers' voice coils. The LF current "might" prefer to flow through this coil depending on the reactive impedance of the following series cap ( also dependant on other circuit resistances. ) I also assume that the 16 ohm series resistor in line with the woofer helps limit the amount of LF current that would want to dump into the mid drivers' voice coil. The woofers' leg seems to be missing the necessary conjugate capacitor for a true series network .
    - The 2 caps ( inline & in series ) with the horn drivers' circuit are electrical complications that I haven't yet fully thought through ( except they represent frequency dependant reactive impedances that are paralleled with the woofers' static load ) . I'm still assuming the woofer is operating without any LC elements on its' lines .
    - To some extent, like all series networks' this circuit will be self balancing due to all the variable impedances. How effective the balance is I don't know since I generally stay away from these sort of layouts. Fun to think about though !

    - ( Hmmmm, new 2410 diaphagms are now quite expensive ) .


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    Todd,

    If this is your wiring setup then,

    - You've got the horns' variable Lpad wired incorrectly ( it's essentially wired upside down which partially supports my initial post on series networks ) .

    - Pin 1 of that variable Lpad should drain to the common ( low potential ) ground side of the circuit.

    - Pin 3 , should pick up the LC "filtered" voltage from the ( high potential ) side of the horn circuit .


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    Quote Originally Posted by Giskard
    Hey! Thanks for the visual Earl. I was starting to wonder why those two weren't talking about the whole mess over the phone.

    I sent off toddalin's questions to someone asking them if they had time to write a Reader's Digest, Condensed Version-type of answer. They were actually good basic questions. We'll see what happens. I suspect they'll end up sending a book title or two instead. That's what I'd do.
    How amusing. At least its in DIY!

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    Quote Originally Posted by Giskard
    Hey! Thanks for the visual Earl. I was starting to wonder why those two weren't talking about the whole mess over the phone.
    You're Welcome !

    But;
    - I didn't create the posted jpg circuit ( as drawn ) . It was from an extremely brief posting of Todds' .

    - Until a "fessed-up" schematic is actually presented, I can only speculate about where this went wrong .


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    You guys jumped the gun. Corrected schematic is included. All caps are Solen with Theta 0.01 mfd by-pass caps. All resistors are Mills 12 watt.








    Quote Originally Posted by Earl K
    Todd,

    If this is your wiring setup then,

    - You've got the horns' variable Lpad wired incorrectly ( it's essentially wired upside down ) .

    - Pin 1 of that variable Lpad should drain to the common ( low potential ) ground side of the circuit.

    - Pin 3 , should pick up the LC "filtered" voltage from the ( high potential ) side of the horn circuit .



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    Quote Originally Posted by toddalin
    "Thanks, at least I know I'm not crazy and my analyzer is fairly accurate in that range. Doesn't my testing demonstrate that it is possible to get rid of the 500 Hz notch, perhaps at the expense of ??? However, with proper crossover design/implementation the notch could be removed without too many other repercussions?
    I think it's important to understand the source and nature of the problem (and whether it's real, of course,) to determine the optimum solution. Crossovers are frequently tuned for specific driver combinations and cabinet configurations, but, as Earl suggests, that tuning must be accomplished in particular ways that do not compromise the primary function. Having begun with the NL200b core, I'd expect this one to be well positioned already.

    I'd suggest, at this point, you'd be significantly better off letting your EQ take out that notch at 500 Hz than adding series resistance to the LF. We need to do more to understand this better, though. If it's phase interference due to geometry, EQing by any means, i.e., externally or within the crossover itself, may produce other undesirable sonic consequences. I can guarantee that adding 16 ohms in series with the woofer is not on the list of preferred approaches....

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    Quote Originally Posted by Zilch
    (7) Alternatively, send me one of the crossovers, and the schematic "as built." I'll break out an LE175 and 2402 here to run with 2235H and test/troubleshoot it....
    - Zilch, if you are going to get into this and help Todd out , then can I suggest that it would be worth your while to also duplicate ( in a mockup ) the physical distances between the woofer & the DLH175 . Assuming the schematic presented is what was actually first wired up , then the acoustic summation between the 2235 and the horn must of just plain sucked ( to force Todd to run the woofer fullrange ).

    - Likely ( maybe obviously ), different lowpass points need to be chosen for the woofer to horn transition . Perhaps leaving out the woofers' 24uf cap and then creating a "blended Zoebel" that is part low pass & part impedance equalizer is a good way ( meaning , economical ) to reclaim some lost midrange .
    - Also, the le175 has less lower-midrange bloom than a le85. Therefore the 3-pole hipass on the horn-circuit might be "tailored" incorrectly for this driver/horn setup . This could easily exaccerbate any inherent FR weakness ( in the 500hz to 1K area ) .


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    Quote Originally Posted by Earl K
    -
    - Likely ( maybe obviously ), different lowpass points need to be chosen for the woofer to horn transition . Perhaps leaving out the woofers' 24uf cap and then creating a "blended Zoebel" that is part low pass & part impedance equalizer is a good way ( meaning , economical ) to reclaim some lost midrange.

    Actually been there/done that. Disconnected the cap entirely as well as trying various resistances between the cap and gnd. Adds very little upper end boost to the woofer, such that it is audible, but the analyzer doesn't see it and the spectrum remains pretty much the same..

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    Thanks you, Earl, for your input here. I think where I'm headed is that the 500 Hz "problem" is apparent in running the woofer just by itself, in this cabinet, with no crossover, which I'm about to further verify in a different room.

    While the blending with the LE175 may also be a factor, my approach is to look at each separately, and the woofer in this box seems to be primary here....

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