Polk monitor 10A contour network

Sumbrada69
Sumbrada69 Posts: 41
in Vintage Speakers
Hello I have monitor 10As and they have a "RC contour network / filter" in the Tweeter part of the crossover before the main 12uF Cap. What is this here for? My 7Bs and 5Bs do not have it. Also, when I upgrade the crossover do I need to use an equivalent quality Cap as the main 12uF? Thanks
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  • F1nut
    F1nut Posts: 50,532
    To make it sound good.
    You should upgrade every cap and resistor including that cheap yellow mylar.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • Gardenstater
    Gardenstater Posts: 4,459
    Sumbrada69 wrote: »
    Hello I have monitor 10As and they have a "RC contour network / filter" in the Tweeter part of the crossover before the main 12uF Cap. What is this here for? My 7Bs and 5Bs do not have it. Also, when I upgrade the crossover do I need to use an equivalent quality Cap as the main 12uF? Thanks

    It is to correct a rising frequency response with decreasing frequency.

    Can you draw the schematic with the values of the components? I didn't know the 10A had a contour network.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    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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  • Sumbrada69
    Sumbrada69 Posts: 41
    Yes F1Nut, I know to upgrade all but not the question. I'm asking if the main series 12uF cap and the contour network 12uF cap need to be the same quality?
    Gardenstater if you look at the schematics page here no. 18775 Polk 10 what I am asking about is the RC in parallel set just after the fuse before the series Cap. From what I can tell it's a contour network / filter. What is it for? Also, what is the resistor in parallel with the tweeter for? Signal reduction due to parallel MWs ? Thanks
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  • F1nut
    F1nut Posts: 50,532
    Yes
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • Gardenstater
    Gardenstater Posts: 4,459
    edited October 7
    Sumbrada69 wrote: »
    Yes F1Nut, I know to upgrade all but not the question. I'm asking if the main series 12uF cap and the contour network 12uF cap need to be the same quality?
    Gardenstater if you look at the schematics page here no. 18775 Polk 10 what I am asking about is the RC in parallel set just after the fuse before the series Cap. From what I can tell it's a contour network / filter. What is it for? Also, what is the resistor in parallel with the tweeter for? Signal reduction due to parallel MWs ? Thanks

    I answered above. Maybe you didn't see. It is to correct for a rising tweeter response with decreasing frequency.

    That schematic (dated 11/26/84) is for the Monitor 10B that had the SL1000 tweeter and then had the SL2000 tweeter. Note the midwoofers are 2 MW6501 in parallel (not MW6500). At this point Peerless had stopped making the KO10DT tweeter and Polk had to transition to their own SL1000, which was around for a short while until they went with their SL2000. In later Monitor 10B and M10 Series 2 they went with the MW6503.

    The resistor in parallel with the tweeter, combined with the series resistor, is part of an L-pad attenuation circuit to voice the tweeter properly with the MW6501s. Don't quote me on this because I'm not an expert in crossovers.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    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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  • Sumbrada69
    Sumbrada69 Posts: 41
    Thanks, the schematic suggested is the same as my 10As with peerless and MW6500s. Same values with fuse. Ok the contour network controls output changed by frequency. The series cap for crossover ~3khz? If the resistor in the contour work with the parallel resistor (L-pad) for voicing, does the Cap in the counter work with or affect the series cap? Does it act like 2 caps in series thus 12+12/2 = 6uF? Later speaker versions also use the contour. I understand some circuit stuff but still learning.
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  • Gardenstater
    Gardenstater Posts: 4,459
    The crossover is 3kHz but I don't know about the caps interaction. There's only so much two non experts can teach each other 🤣, but if you post your questions over at diyaudio.com or audiocircle.com (Danny Richie thread) you will probably get better answers.

    If you haven't read this here is the review of the 10A by Stereo Review in Jan 1980:

    https://www.worldradiohistory.com/Archive-All-Audio/Archive-HiFI-Stereo/80s/HiFi-Stereo-Review-1980-01.pdf

    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    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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  • Sumbrada69
    Sumbrada69 Posts: 41
    Thanks for your information. I will the other forums. Thanks for link.
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited October 7
    I'm pretty sure they don't simply act in series because the first "cap" is no longer a cap but a cap in parallel with a resistor and most definitely will behave differently. Signal can bypass that cap to some degree, through the resistor.

    Let us know if you get any interesting answers in those other forums.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    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
    · Share on FacebookShare on Twitter