Monitor 5B Hidden Gems

2

Answers

  • GardenstaterGardenstater Posts: 1,659
    xschop wrote: »
    before I forget or loose my info....

    Base plate ID.... 1.085"
    Voice coil ID..... 1.010
    Voice coil OD..... 1.060
    Pole piece OD....0.995"

    This all calculates to only 0.010" air gap on either side of VC and and confirms why a 0.020" thick plastic shim half the circumference of VC, inserted between VC and pole-piece will re-center the pole-piece, if you remove the dust cover to accomplish the task.

    Hmm by my math I would've said 3 pieces of .007" plastic shim, located more or less in an equilateral triangle orientation. Or 4 pieces in a cross configuration. radial clearance = 1/2*(1.010"-0.995") = 1/2 * 0.015" = 0.0075"
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    xschop wrote: »
    before I forget or loose my info....

    Base plate ID.... 1.085"
    Voice coil ID..... 1.010
    Voice coil OD..... 1.060
    Pole piece OD....0.995"

    This all calculates to only 0.010" air gap on either side of VC and and confirms why a 0.020" thick plastic shim half the circumference of VC, inserted between VC and pole-piece will re-center the pole-piece, if you remove the dust cover to accomplish the task.

    Hmm by my math I would've said 3 pieces of .007" plastic shim, located more or less in an equilateral triangle orientation. Or 4 pieces in a cross configuration. radial clearance = 1/2*(1.010"-0.995") = 1/2 * 0.015" = 0.0075"

    How would you ensure concentricity between the pole-piece OD and base-plate ID that way?
  • GardenstaterGardenstater Posts: 1,659
    Oh I was assuming the base plate was already centered by a similar process to the voice coil and attached to the basket, using 3 or 4 0.012" shims. 1/2*(1.085"-1.060") = 1/2*0.025" = 0.0125". Unless I'm missing something.

    I'm just trying to understand what you're doing because I may be disassembling a silver basket MW6500 that I have that has voice coil rubbing issues.
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    The known stationary center is the base plate ID since it's riveted to the MW basket. I was referring to resetting the relationship of it to the pole-piece, by way of temporarily using the 0.025" thick wall of the voice coil.
  • GardenstaterGardenstater Posts: 1,659
    Oh ok I thought it was probably spot welded. Well if the pole piece + magnet are off and the dust cap is off, can't you use the 0.012" shims to verify centering of the voice coil with respect to the base plate? I don't know what you'd do if that is off, because probably the only way to fix it would be to separate the surround from the basket and reglue, but assuming it is good, can't you just use the 0.007" shims through the dust cap hole to center the magnet+pole piece assembly with respect to voice coil?
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    If done that way,there would be no way to tell if the OD of the voice coil landed concentric to the ID of the base plate.
  • GardenstaterGardenstater Posts: 1,659
    edited May 2020
    I guess I was thinking that it could be done by feel and a light touch, so as to not displace the voice coil/cone/spider assembly to go out of concentricity to the base plate pole piece? Maybe that's impractical, but I was thinking it'd be a similar process to setting valve clearances with a feeler gage on a car, except in this case you're trying for the same relative drag with all 3 feeler gages. I guess the feeler gages would have to be very narrow for it to work.
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    edited May 2020
    Give it a try. However your method, there needs to be 0.010" air gap between Voice coil OD and Base plate ID

    That said, the limiting factor for a precision reset via a jig is the Base Pate OD, being stamped steel (crap manufacturing IMO).Both mine measured out-of-round by a couple thousandths. It still can be done, of course with the dust cover in-tact, as many have done previously.
    The sheet rock screws and PVC pipe aren't my style and a crap-shoot on final pole-piece concentricity.
    That also said, I'll build a couple with a precision design in mind with 1/4-20 dog-point Allen head set screws and 7075 alloy housings that can be reset by calipers...

    iqx7uv8wjkyw.png
    Post edited by xschop on
  • GardenstaterGardenstater Posts: 1,659
    edited May 2020
    I see what you are doing now. Pardon my hashing it out but it enabled me to understand in the end. You are utilizing the flexibility in the rubber surrounds to find the center of the pole piece with your half circumference 0.020" flexible shims. You first put it in place where you visibly see the largest gap and then push the pole piece + magnet assy over in that direction until shim is tight and then (ultimately) allow the glue to set up while maintaining that position. 1/2* ((1.085-1.060) + (1.010-0.995)) = 1/2*0.040" = 0.020".

    Too bad about the stamped steel and resulting out of roundedness. I'm anxiously awaiting your completion of the higher precision jig you are working on.

    PS: I don't know how practical my method in my post above would be because it would probably be very difficult to do by feel but it might have the saving grace of compensating for a speaker that has the voice coil OD out of concentricity with the base plate pole piece initially, but maybe not so bad that it is a reject speaker.
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    edited May 2020
    Exactly. And as an aside note, you can get away with 1.375" width of the 0.020" plastic, only inserted to 3/16" depth to facilitate easy shim removal. The strength of the magnet keeps the axial alignment of the pole piece, not having to rely on full-depth shim insertion.
  • xschopxschop Posts: 1,968
    Question to confirm... When you put positive 1.5 DCV to positive MW terminal, the MW cone should protruded outwards?

    irvol3h4c46a.jpg
  • F1nutF1nut Posts: 45,420
    Correct
    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

  • xschopxschop Posts: 1,968
    Thanks, the acetone stripped the markings off. Just by flipping the magnet on pole-piece it indeed changes direction when battery applied
  • xschopxschop Posts: 1,968
    edited May 2020
    Also, Inspecting the passives, the spider cloth material itself tore about half the circumference around near where it meets the cone. It didn't delaminatefrom the cone, just sheared the cloth due to age and high movement. Will the two thin layers of Eileens tacky glue be a long term solution?. It seems to be strong and flexible so far....
    gv02oqgah1o8.jpg
    Post edited by xschop on
  • F1nutF1nut Posts: 45,420
    Aleen's glue should do the trick.
    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

  • xschopxschop Posts: 1,968
    edited May 2020
    F1nut wrote: »
    Aleen's glue should do the trick.

    Looks like it's holding so far. I did a quick test of that one at high volume/bass for about 10 minutes.
    I started carefully removing the old vinyl from the enclosures.
    Went with Blue Loctite as it gives alot more work time while setting magnets with plastic shims.
    The recent Peerless MWs look like they used Blue Loctite as well.

    Would a net mass gain of @ 4 grams to the PR cones affect resonant freq. much from factory?



    vila0tik0zza.jpg
    Post edited by xschop on
  • xschopxschop Posts: 1,968
    edited May 2020
    As with all these vintage Polks, I removed about a pound of glue drippings from the inside walls....

    h4petzg2e9ih.jpg

    The new terminal plates allow for wider hurricane nut placement. Interestingly, The factory PR mount holes do too. It's the factory MW hole distances that would require @ 1/8" trim on their edges....

    ezs4z9lwsjcv.jpg

    ptr9f5bqjunb.jpg


  • F1nutF1nut Posts: 45,420
    Would a net mass gain of @ 4 grams to the PR cones affect resonant freq. much from factory?

    Absolutely
    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

  • xschopxschop Posts: 1,968
    Do most folks just toss the PR if the spider tears? They seem paper thin and fragile, even with the repair. Just thinking ahead, a straight guide pin can be made and inserted/glued thru the PR disc on front cone and then held in back by a simple nylon/teflon disc that is centered and glued to the basket hole. The old spider would not be needed...
    What you think.

    ykgnenklizd7.jpg
  • GardenstaterGardenstater Posts: 1,659
    Doesn't the spider have a spring constant, even if it is a low one? Wouldn't you have to have a fine wire compression spring in there, so that it tends to want to keep the cone retracted into the cabinet?
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    Doesn't the spider have a spring constant, even if it is a low one? Wouldn't you have to have a fine wire compression spring in there, so that it tends to want to keep the cone retracted into the cabinet?

    If indeed that is a design parameter, then yes. I was thinking they were more for axial alignment through the stroke and the very thick Butyl rubber surround held majority rebound. When you push on the spiders they are paper thin.

  • xschopxschop Posts: 1,968
    After further/close inspection of both PRs, I agree with you GS, @ the spring aspect of the spiders. How much forward/aft force they exert is the unknown.
  • xschopxschop Posts: 1,968
    edited May 2020
    Practicing with the Exact-O again. 0.080" thick PVA foam, 1.0" ID x 1.7" OD covers the VC leads nicely.
    I'll pick up some 1/8" thick open cell black foam and use this piece to trace them out....

    w7pydkvgfoch.jpg


  • GardenstaterGardenstater Posts: 1,659
    Looks nice! Will it have enough clearance so it doesn't rub on the phase plug?
    George / NJ

    Polk 7B main speakers, most mods comp. (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
  • xschopxschop Posts: 1,968
    edited May 2020
    Looks nice! Will it have enough clearance so it doesn't rub on the phase plug?

    It can't as the voice coil protrudes forward of the cone by about 1/8" acting as boundary. Luckily I was skiddish with the scalpel and left about same height of dust cap glue near the cone too acting as boundary for OD of the foam.
  • xschopxschop Posts: 1,968
    Settled with 1/8" thick crafters felt and 3 ml syringe with Q-tip for Aileens. The felt conceals the VC leads and weighs next to nothing.

    Next up will be the cabs. Has anyone used the Forged Hammer Black paints before?

    ovcbmbz322yc.jpg

    6kzyc2upgoyd.jpg

  • F1nutF1nut Posts: 45,420
    I tried the hammer paint on something, didn't like it one bit.
    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

  • xschopxschop Posts: 1,968
    Back on this project again. I started working on the factory Polk emblems to give them the brushed-billet look against the black cloth. I noticed that the grill frames on the vertical sides of cabinet are curved inwards due to age. The cloths are in excellent shape and I would like to remedy this without having to remove and re-staple grille cloths. Anyone have a suggestion?
  • xschopxschop Posts: 1,968
    edited June 2020
    So I was at the shop and got to thinking the frame MDF are a little over 3/8" thick and 7.32" inner widths at top and bottom where they meet at corners. So I made some billet rods at 7.32" not including 0.175" dia. by 0.175" length spuds to countersink and glue into the MDF between Passive and MW midlines. It brings the cloth back tight and parallels straight....

    Now I just need to find my right-angle drill attachment.

    pxx178kiea0c.jpg

    aa53bm8wykh5.jpg


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