B&O CX100 crossover enigma

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xschop
xschop Posts: 4,707
in DIY, Mods & Tweaks
I'm going to start modding these for another near-field setup and want to experiment with padding the tweeter with a 0.5 or 1.0 ohm resistor.

Just getting opinions, where would I insert the resistor into the diagram here (found off the net)
Wish there were a schematic diagram to make things easier to decipher lol.

exr28nwymk05.jpg
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  • Gardenstater
    Gardenstater Posts: 4,190
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    I'm thinking you put the resistor between the 6.8uf capacitor and the negative terminal of the binding post.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Ill give it a go. I've got some spare Mills 1.0 ohm and Clarity PXs just showed up.... Might well so wires while I got it all apart. The way the rear panel is, I can mount it externally and easily test different resistors...

    y7618prt7kan.jpg

    63bpsp4nn7xf.jpg

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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Piggy-backing an Xover makes things ALOT easier for sure. Not @VR3 fancy, but'll do for testing.... Guess I better listen without resistor first and burn some Clarity's in...

    1b6by2qt6lmn.jpg

    c9fz92ksntk9.jpg


    txl78qpc4jrb.jpg
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    While waiting on the new Wu-rubbers, I've started dissecting the midrange for uber mods...
    Will have to shorten a set of MW65xx plugs, but they drop right in with B&O pole-piece ODs being 0.997, same as Polk🙂

    z66bsotv78tl.jpg

    93t5nr7awjdv.jpg

    37yn92d7n9oi.jpg

    Fiber backed neoprene rubber to ensure a good seal around the thin metal baffles and extra damping to boot with the Polyurethane coating on the frames. They'll get a layer of black latex after full cure....

    fkrwfzhy5syp.jpg

    danl9nlj1px9.jpg

    9pzsvf7e43zd.jpg

    Here we lost a lot of weight from a very thick and coated paper dust cap. I gave them one light coat of latex doping compound...

    jgm8llm9tknn.jpg

    B&O upped their game along time ago...

    thmguqgxchml.jpg









    Post edited by xschop on
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  • xschop
    xschop Posts: 4,707
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    The alloy housings are built solid quality, but have a slight ring being only 0.180" thick.
    The butyl mat quiets them down very good where only thumps are heard when tapping on all sides....

    ywyu1k4qehs0.jpg

    ny73tlbqdo0c.jpg

    vax0dbvcid7u.jpg

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    5qs069asj1z8.jpg


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  • ChrisD06
    ChrisD06 Posts: 886
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    xschop wrote: »
    B&O upped their game along time ago...

    thmguqgxchml.jpg

    Is that tweeter magnet shifted or is this just due to camera perspective?
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  • xschop
    xschop Posts: 4,707
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    Camera. They even have damn good glue lol
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  • Gardenstater
    Gardenstater Posts: 4,190
    edited July 2023
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    Whoa! That is one major bored out pole piece there! Is that a chunk of open cell foam? Does the hole go all the way through in the back or is it an acoustically damped chamber? I see they even rounded the upper edge of the pole piece presumably to diffuse the reflections there.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Open-cell within a cast hyperboloid and a foamed backchamber. B&O did all the XS-modding already lol.
    They left at least one thing I can mod.
    The consensus is that plastic diffuser needs to be cut off. I'll machine some billet bezels for these sans diffuser.
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  • Gardenstater
    Gardenstater Posts: 4,190
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    Pretty small drivers. Phase plugs will result in about 8 to 10% reduction in Sd in this case. Are the replacement surrounds butyl or the original foam?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
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    Butyl. Hopefully that helps. But not plugging the lower woofer as I think this is technically a 2.5 way design
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  • Gardenstater
    Gardenstater Posts: 4,190
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    It's a pretty crazy crossover. I found this, which doesn't exactly clear things up totally, at least not for me (lol). This person seems to think the upper woofer only receives the lowest Hz signal.

    ryxkeox9c2ao.jpg
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Do you think they flipped phase of the tweeter because of 6.8uf on NEG side?

    The other enigma is the lower woofer pole-piece is vented, the top "midrange" is not.
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  • Gardenstater
    Gardenstater Posts: 4,190
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    If what the guy on Audiocircle said is correct, the upper one is the woofer and the lower one is the midwoofer. That would make sense? because you would have more need of a vent on a midrange?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
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    I would normally assume vented pole piece for woofer, if the vent was on midrange, there'd be coloration by bass waves affecting the midrange cone.

    They both have 5.1 DCR
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  • Gardenstater
    Gardenstater Posts: 4,190
    edited July 2023
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    xschop wrote: »
    Do you think they flipped phase of the tweeter because of 6.8uf on NEG side?

    The other enigma is the lower woofer pole-piece is vented, the top "midrange" is not.

    I think that the small inductor and the large inductor are in series for the top woofer and inductances in series add and the larger the inductance the lower in Hz is the low pass filter. So I think I agree with the Audiocircle guy that the top one is the woofer that receives only low frequencies. Would be good to measure the inductances of the two coils.

    For the tweeter high pass circuit, I don't think it matters whether or not the capacitor is on the positive wire or the negative wire, just that it is in series with the tweeter.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Ah, Ok I see what you/they are saying. The midrange (Lower MW) relies on roll-off after the small inductor. So I guess B&O got more performance from the midrange by adding a vent for pistonic speed.

    Also makes sense that they had the midrange angled slightly upward as these set on a credenza or desk.

    Maybe I'll just run these as woofers as phase-plugged mids and run the original midrange as a vented woofer? What's nice is I can also flip the cabs and have a listen too while on PC rig.
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  • xschop
    xschop Posts: 4,707
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    As for tweeter, wouldn't this have made more sense?

    gblhw5xzygn4.jpg
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  • ChrisD06
    ChrisD06 Posts: 886
    edited July 2023
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    Question: Why not measure the DCR of the coils and build a new crossover, this one seems really simple. Correct me if I'm wrong, but the tweeter has a first order high pass, and then one of the woofers is being run full range and naturally rolls off with the other having a first order low pass and acting as a bass driver?

    Super simple design, and I mean you can use natural roll off and make it sound nice (the 1992 Monitors from Polk did this) but why not go the extra mile?
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    Calling @westmassguy lol. Strange looking crossover scheme here. Even trumps early Polk production Hail-Marys. :D

    I'll pull inductor coils tomorrow and get DCR and mH's
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  • ChrisD06
    ChrisD06 Posts: 886
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    xschop wrote: »
    Calling @westmassguy lol. Strange looking crossover scheme here. Even trumps early Polk production Hail-Marys. :D

    Ill' pull inductor coils tomorrow and get DCR and mH's

    Do you use the kelvin sense lead method to measure DCR? https://www.debassociates.com/blog/inductor-dcr-measurement/
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  • xschop
    xschop Posts: 4,707
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    I just use my trusty Wu-Bay LCR digital meter with loop leads.
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  • ChrisD06
    ChrisD06 Posts: 886
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    Wu-bay? That's a new one, I'll group that one with "Chinazon"
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  • xschop
    xschop Posts: 4,707
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    Whether it be brass binding posts or DIY kits for serial-passaged forced evolutionary chimeraviruses, the Wu-bay has it.
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  • Gardenstater
    Gardenstater Posts: 4,190
    edited July 2023
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    xschop wrote: »
    As for tweeter, wouldn't this have made more sense?

    gblhw5xzygn4.jpg

    One would think so but I've learned to never underestimate the Krauts because there is usually a method to their madness.

    JAT - If swapping drivers and adding phase plug lowers their sPL at all you might try lowering the DCR of the inductor(s).
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    These little jewels are hefty for their dimensions...

    txqt52qj4zdo.jpg



    Old cap...

    u16ft21rvim1.jpg

    New cap (Same Clarity Cap now residing on 5B tweeter circuit)...

    5u6fsoibyiqe.jpg

    Factory small coil....

    io30pbsesro6.jpg

    Factory large trans coil....

    epjopck66vc2.jpg

    Factory gaskets not positioned/sealed well. Don't look to have been opened, but stuffing is different that other net-pics I've seen...

    tgm4sblwbbpb.jpg

    evkldc1czvef.jpg




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  • Gardenstater
    Gardenstater Posts: 4,190
    edited July 2023
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    There are sealed chambers for each driver? Or are those just open braces? Is there a bass reflex port?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    No port. All open chambers (3rd pic down from enclosure dampening pics).

    Factory tweeter foams about rotted, shrunk. Glad I got extra wool tweeter pads from @VR3. Trimmed edges and 2.5" center hole and they fit perfect. Look darn sweet too...

    zuyjmgi8ltr4.jpg

    k0rj5b4sd3z2.jpg

    Here's the lower midrange angle... Looks to be 10°

    fzfb5jvnlg7a.jpg

    7uzado7e11k5.jpg











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  • ChrisD06
    ChrisD06 Posts: 886
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    Port it and add a power port 😂

    Seriously though, I think I already mentioned this but replace the ferrofluid in the tweeter if there was any.

    Or... if you want to get ballsy, add some anyways and see what happens 🤷‍♂️
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  • xschop
    xschop Posts: 4,707
    edited July 2023
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    There was no dried FF on the coils. Will simply swap out the foam plug for lamb's wool.

    Dual Polyurethane/Latex layers are cured and baskets no longer ring when thumped...

    snicz1i5k7eo.jpg

    Before I install new butyl surrounds, the midranges' inner frames will get some foam.🙂
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