Polk Audio Monitor 10 A what's this frosting powder on basket and magnet

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speks
speks Posts: 3
in Vintage Speakers
Hi guys, first time posting here,

So recently i buy from a guy this speakers, they sound pretty good, not distortion what so ever.

I started to investigate on this speakers, when i found out about the common problem of the shifting magnets, 3 of the 4 mid drivers produce a scratching sound when i push in with just one finger on the outside of the cone, if I push in with two or more fingers evenly no scratching sound is produce.

Once in my home i realice the speakers wherer like "gunky", i clean them up and theres no signs of watter damage on the cabinets.

So i decided to take out the driver and this is how it is, with a frosting like powder in the metal plate that sandwiches de magnet, i actually ended up taking out both of them, and they are the same.


Is this toxic? Hoy can I tell if the magnet have shift or misaligned?

Can i fix it?

Last questions, this speakers have the peerlees twitter, when I was testing them i felt air coming out of the twitter, they have the hole in the center, just wantend to know if this is normal?


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Thanks in advace for all the help.
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Answers

  • F1nut
    F1nut Posts: 49,802
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    I already answered this on the other forum you posted on.
    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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  • subkron
    subkron Posts: 57
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    @F1nut Can you supply the link to the answer or put it here? I have a set lying around w/this stuff, searching for white powdery didn't turn up anything definitive, thx
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  • speks
    speks Posts: 3
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    @subkron here's the link, but no specification on the white powder, i suspect that's it's part of the oxidation of the basket, since the magnet itself does not have corrosion.

    Maybe galvanized corrosion?

    https://audiokarma.org/forums/index.php?threads/polk-audio-monitor-10-a-frosting-like-on-basket-and-magnet.1009032/
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  • Gardenstater
    Gardenstater Posts: 4,187
    edited October 2022
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    The white stuff is zinc hydroxide which forms over time when the zinc coating reacts with water and air and it gradually consumes the zinc coating. Most likely to occur where humidity is high and air circulation is lacking. These speakers were probably from a humid climate like the seashore.

    https://www.orrconsteel.com.au/sites/default/files/White-Rust-White-Paper-200531.pdf

    You've got the MW6500 drivers which I have in my 1979 7Bs. Unfortunately they are more subject to voice coil rubbing as the suspensions sag with age. The clearance between the OD of the voice coil and the basket plate is much tighter than in later drivers.

    You may have incipient rubbing if there is one quadrant where, when you push on the cone it tends to rub but not the other 3 quadrants. You may or may not begin to hear distortion from time to time when you are playing certain music that is closer to the resonant frequency. It is a good sign if pushing evenly on the cone all around with 4 fingers, doesn't produce rubbing.

    It couldn't hurt to rotate the drivers 180deg from the position they have been stored in.
    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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  • speks
    speks Posts: 3
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    Gardenstater thanks for the info! I'm gonna rotate the drivers 180, also clean them up. Would you suggest applying oil for prevention would be a good idea?
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  • F1nut
    F1nut Posts: 49,802
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    No oil
    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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  • boston1450
    boston1450 Posts: 7,472
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    As stated. Use 2 or more fingers "evenly" so your applying pressure to woofer evenly as you push in/out to check for shifted magnets.. Using 1 finger isn't going to work.. I think you answered the question, that your woofers are fine. Which is great.. As I learned here on Forum use real Windex for woofer surrounds
    ..
    ..
    ..
    Randy/Maine
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