6500 anomaly

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  • MrGeology
    MrGeology Posts: 83
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    F1nut wrote: »
    MrGeology wrote: »
    F1nut wrote: »
    I knew that wasn't a Polk driver just by looking at it and said so earlier.

    This is true. But when someone tells me the sky isn't blue I need an explanation rather than a statement.

    Ummm...look up...lol

    Yep, that is certainly better than an explanation lol
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • Gardenstater
    Gardenstater Posts: 4,288
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    Did you get a chance to determine if the Polk MW6500 voice coil is flattened wire for edge winding or not? I'm guessing not but still wondering.

    9zzyx6atbhhx.png
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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  • pitdogg2
    pitdogg2 Posts: 24,950
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    I thought edge winding came along much later than the mw6500 was used.
  • Gardenstater
    Gardenstater Posts: 4,288
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    pitdogg2 wrote: »
    I thought edge winding came along much later than the mw6500 was used.

    That is what I "surmise" especially since they may have increased the gap after these, but have you ever heard anyone from Polk tell us when it came about? Doesn't hurt to check these out of curiosity.
    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
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    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
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  • xschop
    xschop Posts: 4,847
    edited April 2023
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    I don't think so for edge wound. Heck I'm still waiting for the touted copper-plated pole-piece units that Polk said they made.

    tchtmk345sr8.jpg

    This one also has a completely detached spider at the VC that I finally got glued back properly. Once it dries then I'll Dremel the ID out slightly to match the 6.5ohm replacement coil OD.

    halw7brohrsk.jpg

    j7r49cneeaqx.jpg


    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
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    Cool. Another question (sorry :) )......is the voice coil one layer or two? It kinda looks like two when I zoom in to your photo at the paper towards the back end of VC.
    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
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  • xschop
    xschop Posts: 4,847
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    And the glue I tried is no joke.... No rivets or fasteners will need to be replaced and will allow plenty of adjustment time around VC when time comes...

    7nm7o3zme2ix.jpg


    byndoywcrjdc.jpg
    Don't take experimental gene therapies from known eugenicists.
  • xschop
    xschop Posts: 4,847
    edited April 2023
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    Glad you asked before I trashed. I measured a single wire strand at 0.008" and peeled back a layer that was 0.016" so it must be dual layer. Looking under mag glass looks to be the case as well and looks like CCA wire too.



    Don't take experimental gene therapies from known eugenicists.
  • xschop
    xschop Posts: 4,847
    edited April 2023
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    Maybe I misunderstood BL explanation. I Thought it was actual length of wire itself from definition.

    From Web...The force factor BL is calculated from the following formula:

    BL = B (The flux density of the magnet) x L (The length of voice coil wire in the magnetic gap)

    The 6500 coil length itself is 0.500 and the POKE-Gefco is 0.350, both have same DCR @6.5 ohms.

    glsyzzd1qs66.jpg
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
    edited April 2023
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    The plot thickens :) . Is it possible to measure wire dia. on Poke - Gefco without damaging the VC, to compare to 0.008" dia. of 6500 VC?

    Depending upon dia. of VC wire, it may even be 3 layers vs. 2 layers for the 6500. We should be able to calculate the no. of layers, assuming perfect lay.
    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
  • xschop
    xschop Posts: 4,847
    edited April 2023
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    @MrGeology said the Poke is expendable...
    The Gefco has more turns and a tighter winding due to smaller dia. wire (0.006). It is also dual layer.

    rw8xcxjsk08q.jpg
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
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    So assuming they are both CCA wire of same resistivity, the L value for the Poke - Gefco would be 33% greater than L value for 6500. That also assumes 2 layers for both. If 3 layers for P - G, then it has L value 3.99/2 = 99.5% greater L value.

    If magnet grades are the same and ID and OD are same, and if B is proportional to magnet heights, then 6500 has a B value that is 26% greater than P-G.

    I could see P-G possibly having greater BxL.
    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
  • xschop
    xschop Posts: 4,847
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    Looking under mag glass and using blade to scrape ends, the Gefco wire looks like solid copper.
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
    edited April 2023
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    2 layers each. OK then BxL are almost the same I'd say. Actually could even be about 6% greater for Poke -Gefco driver.
    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
  • xschop
    xschop Posts: 4,847
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    Warped basket, crap glue job, no cone doping and janky spider. So many problems with this driver, should be made by GLICco.
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
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    RIP 🙏
    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
  • xschop
    xschop Posts: 4,847
    edited April 2023
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    Spider glued dry and strong. Dremeled cone ID to match new coil. It is about .200" taller when coils are properly set, but it'll fit under factory felt cap no problem. I"m still going to take it down .100" inch with Dremel for good measure.
    I didn't want to wait 3-4 weeks again for another 3.5 ohm coil, or I would have put one of those in and kept it as back-up for 6511 duty.

    ua1w06pv47na.jpg

    iiqcqglt2105.jpg

    8i7cykzvcksz.jpg





    Post edited by xschop on
    Don't take experimental gene therapies from known eugenicists.
  • xschop
    xschop Posts: 4,847
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    Don't take experimental gene therapies from known eugenicists.
  • MrGeology
    MrGeology Posts: 83
    edited April 2023
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    The 6500 replacement for the oddball got here yesterday. It is stamped 1980 and is in really good condition with no coil rub.
    Here is what DATS turned up for its TS parameters.
    dcdioid7z8ea.jpg
    wqi7ym7g8wp0.jpg
    Ran it through the DATS process half a dozen times with no significant changes to results. The oddball never came up with the same results twice, and probably tested it around 30 times.
    The TS parameters of this new (circa 1980) 6500 are pretty far off from the "official" specs, however did listen to it a few hours last night in one of the 7Bs and it sounds really good. Am surprised at the low frequencies these speakers can carry, love the 7B!
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • Gardenstater
    Gardenstater Posts: 4,288
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    We can add your name to valued forum members list who are owner/operators of DATS! That is very interesting, especially since it gives a couple important data points for MW6500 (sample of 1 lol) that we didn't have, namely efficiency of 90.9 dB and min. impedance of 7.0 Ohms. Thanks!

    I wonder how much variation in T/S parameters there now is with these vintage drivers vs. when they were freshly fabricated. You probably have a better idea with your samples you have tested.
    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
  • xschop
    xschop Posts: 4,847
    edited April 2023
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    Im sending back another factory 6500 for Michael.

    What's interesting is this good one has a more stiff suspension than the burnt VC 6500 I just repaired.

    Age related or just rode hard and put away burnt?

    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,288
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    xschop wrote: »
    Im sending back another factory 6500 for Michael.

    What's interesting is this good one has a more stiff suspension than the burnt VC 6500 I just repaired.

    Age related or just rode hard and put away burnt?

    Good question. I have heard many a reviewer state that a generally accepted rule of thumb for new speaker breakin is 200 hours or so. Whatever the time is the obvious conclusion is that something changes. Is it that the suspension loosens up or is it that the material of the VC "burns in" or is it both?
    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
  • MrGeology
    MrGeology Posts: 83
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    We can add your name to valued forum members list who are owner/operators of DATS! That is very interesting, especially since it gives a couple important data points for MW6500 (sample of 1 lol) that we didn't have, namely efficiency of 90.9 dB and min. impedance of 7.0 Ohms. Thanks!

    I wonder how much variation in T/S parameters there now is with these vintage drivers vs. when they were freshly fabricated. You probably have a better idea with your samples you have tested.

    Interesting. I thought I must be one of the last people around with a DATS unit since I am relatively new to home audio (started my first home system build around March 2021).
    This is the only 6500 that I have actually run through DATS (most of my Polk drivers are 6502). When the other one gets back from @xschop will run it and post results, I think they are 3 years different. The 1980 one is the non-painted version.
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • MrGeology
    MrGeology Posts: 83
    edited April 2023
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    xschop wrote: »
    Im sending back another factory 6500 for Michael.

    What's interesting is this good one has a more stiff suspension than the burnt VC 6500 I just repaired.

    Age related or just rode hard and put away burnt?

    Not sure if they were a one owner set, but the burnt one came from the cabinet on the left in the picture.h02yqfz71ov4.jpg
    Post edited by MrGeology on
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • MrGeology
    MrGeology Posts: 83
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    The original 7B driver arrived today from @xschop. Thanks again for re-setting the magnet.
    Date on back reads 10583. Here is what DATS turned up for its TS parameters.
    adlds2gio9zi.jpg
    vumwlmrby7tn.jpg
    Ran it through the DATS process a total of 4 times with no significant changes.
    Swapped it into the cabinet where the 1980 driver was so could re-test that one in DATS.
    Here is what DATS turned up for the 1980 drivers TS parameters today.
    ut5ynzca3ogw.jpg
    hjamncvhp7d6.jpg
    Temperature in workshop feels maybe 5 degrees cooler today than first day it was run.

    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • Gardenstater
    Gardenstater Posts: 4,288
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    Thanks! Curious about test lead resistance of ~0.5 Ohms (that's a lot!). Do you have to subtract that from Re to get the voice coil measurement or has DATS already done that?

    Also, with Le measurement, can you tell DATS to do it at 1kHz instead of 10kHz? For a midwoofer it might be more appropriate. Or maybe it doesn't make much difference?
    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
  • xschop
    xschop Posts: 4,847
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    I got the burnt VC 6500 repaired. What do you think would change in TS parameters from using the new VC with the 4 extra holes that now reside in the area between top of pole-piece and dust cap?

    Polk's later drivers have these holes in their VC's.
    Don't take experimental gene therapies from known eugenicists.
  • MrGeology
    MrGeology Posts: 83
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    Thanks! Curious about test lead resistance of ~0.5 Ohms (that's a lot!). Do you have to subtract that from Re to get the voice coil measurement or has DATS already done that?

    Also, with Le measurement, can you tell DATS to do it at 1kHz instead of 10kHz? For a midwoofer it might be more appropriate. Or maybe it doesn't make much difference?
    Both of my handheld meters read 6.5 ohms on both of the speakers. However, DATS measures the resistance of the circuit across the entire frequency spectrum specified (10Hz to 20kHz in the posted pics) and then gives the average resistance over said frequency range.

    The Le measurement is simply the inductance of the coil, measured in miliHenry (mH). I think the max DATS can measure is 10K mH but it is auto ranging. Again, it has to sweep the coil through the entire spectrum in order to determine what frequency is the cut-off. My handheld LCR reads 0.5mH on the 1980 6500.
    The inductance of any coil changes with temperature, which was hard to figure out when winding coils at home. Workshop is about 8 degrees F cooler at night than in day.
    (Mark freshly wound coils, come back that night when workshop cooled off and all inductors had changed values? WHAT? re-mark coils, come back next day when shop is warm, all coils now read what they did yesterday and not what they read last night? Turns out it is the temperature that makes the change, bigger coils see more pronounced changes due to temperature).

    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States
  • xschop
    xschop Posts: 4,847
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    I measured 6.6 ohms at the terminals after new coil install. I liked how this 6500 didn't come with the ugly paper surrounds also.

    Its much harder to set by eye with the black aluminum, but here are the relief holes in VC...

    57hfrrzgj9wz.jpg
    Don't take experimental gene therapies from known eugenicists.
  • MrGeology
    MrGeology Posts: 83
    edited April 2023
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    A few tests I just ran, back to back, on a home-wound inductor and the 1980 MW6500. First tested with the handheld LCR then with DATS. All test completed within 20 minutes or so.
    A 0.745 mH 14 AWG inductor I wound August 2022.
    wu414h9qo6dj.jpg
    zl0r72ynxsll.jpg
    60ghe8qd0bid.jpg
    Same inductor with DATS.
    8bqb9lg9iey7.jpg
    ctt2c5872rkc.jpg
    522l2hhs8nyt.jpg

    The 1980 MW 6500 on LCR.
    exd5xmei6ofm.jpg
    3zljcp5nvbvz.jpg
    The 1980 MW 6500 on DATS (Free-Air only, no VAS measurement).
    c3f53yr79sl0.jpg
    8xg4vqo4zwn4.jpg
    qqqth00ctkho.jpg

    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
    -James K. Polk, 11th President of the United States