6500 anomaly

13

Comments

  • MrGeology
    MrGeology Posts: 83
    xschop wrote: »
    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

    Maybe M(ms) but don't think the holes would reduce the weight by any significant amount. Perhaps Q(ms) if the holes cause/allow air flow related interference or relief. For that matter could also affect F(s). Overall would guess the T/S changes due to those holes is probably negligible (i.e. indiscernible from margin of error).
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    It would be interesting to see how it effects leakdown test times. I can say that my early 6500s with no holes in VC former take forever to leak down.

    Instead of the air having to go through spider, down around the voice coil, and out through the dust cap, it can skip the step of having to go through the narrow annular gap on the inside of voice coil.
    George / NJ

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  • MrGeology
    MrGeology Posts: 83
    edited April 2023
    Gardenstater wrote: »
    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?
    You know, looking at the graph it appears that DATS is reporting the lowest resistance encountered through the sweep as the R(e).
    Haven't found any information on whether the test lead resistance is automatically subtracted. However if it were automatically subtracted, why would they even bother to leave the info on there.
    When testing inductors, resistors and caps the test lead resistance is definitely compensated for by DATS.
    The test lead resistance is near zero for most of the sweep (up to about 6kHz), max resistance from leads occurs at 20kHz, and that is the resistance reported as R(t). Took a screenshot of the test lead calibration (look at blue line on bottom for test lead resistance).n1pws7ada345.jpg
    Gonna go out on a limb and suggest that the R(e) reported by DATS *may* be affected by the drivers momentum at any given frequency.
    Post edited by MrGeology on
    "One great object of the Constitution was to restrain majorities from oppressing minoritites or encroaching upon their just rights."
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  • xschop
    xschop Posts: 5,000
    Gardenstater wrote: »
    It would be interesting to see how it effects leakdown test times. I can say that my early 6500s with no holes in VC former take forever to leak down.

    Instead of the air having to go through spider, down around the voice coil, and out through the dust cap, it can skip the step of having to go through the narrow annular gap on the inside of voice coil.

    This definitely shouldn't matter as it has the solid felt dust cap.
    Don't take experimental gene therapies from known eugenicists.
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    xschop wrote: »
    Gardenstater wrote: »
    It would be interesting to see how it effects leakdown test times. I can say that my early 6500s with no holes in VC former take forever to leak down.

    Instead of the air having to go through spider, down around the voice coil, and out through the dust cap, it can skip the step of having to go through the narrow annular gap on the inside of voice coil.

    This definitely shouldn't matter as it has the solid felt dust cap.

    Hmm. But you did say that Polk used the holes in the later models which have the more gauzy clothlike dust caps?

    Perhaps they were both designed to help with voice coil cooling by ventilating the airspace above the pole piece better? Cooler pole piece translating to cooler voice coil?

    If the airspace in the enclosure acts as a spring of sorts (esp. with acoustic suspension speakers), perhaps even in a passive radiator or ported speaker it will enable the cone to move more rapidly and respond to transients more quickly.

    Maybe it will effect Vas.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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  • xschop
    xschop Posts: 5,000
    edited April 2023
    Glue is drying, then I'll send to Mr Geology for testing :)
    Don't take experimental gene therapies from known eugenicists.
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  • MrGeology
    MrGeology Posts: 83
    Gardenstater wrote: »
    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?
    Actually you are right here again. DATS does have a setting to change it to 1kHz. Ran the 6500 and it now shows the L(e) to be the same as the handheld LCR.
    Maybe you should have a DATS, I can't even seem to figure out the simplest thing like that without a hint. Can't figure out why it would make a difference, but it did. Now have to re-read all about inductance so don't make anymore erroneous statements.
    j7opa9qm7u0g.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
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    Don't feel bad and thanks for the data. You can really help our database on the vintage drivers. Even DarqueKnight measured Le of the MWs at 10kHz so you are in very good company I'd say :)

    PS: Do you have any Polk made tweeters to measure sensitivity on?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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  • MrGeology
    MrGeology Posts: 83
    Gardenstater wrote: »
    Do you have any Polk made tweeters to measure sensitivity on?
    Yes, but am afraid to (added mass is tricky with tweeters).
    Have a set of M7 Series 2, a set of M4A and a set of M4.6 Series 2 as well as the M7B. The 7B are Peerless tweets, forget the others but think they are SL2500 except the M4A, no idea what tweets those have.
    "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
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    Morning research verifying that Le is very nonlinear and varies with both frequency (I didn't know how much!) and displacement (I did know) of voice coil. Shorting rings are to deal with variation due to displacement, but afaik we don't have that in any of the Polk MWs or tweeters.

    https://www.klippel.de/fileadmin/klippel/Bilder/Know-How/Literature/Papers/Voice_Coil__Impedance_04.pdf

    5ujglgywh8mw.jpg
    Post edited by Gardenstater on
    George / NJ

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  • Gardenstater
    Gardenstater Posts: 4,456
    This link explains a bit more:

    http://diy-audio.narod.ru/litr/Le.pdf

    htmf5eqkepmb.jpg
    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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    Custom Steve Wilson 1m UPOCC Interconnect
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  • xschop
    xschop Posts: 5,000
    edited April 2023
    Gardenstater wrote: »
    xschop wrote: »
    Gardenstater wrote: »
    It would be interesting to see how it effects leakdown test times. I can say that my early 6500s with no holes in VC former take forever to leak down.

    Instead of the air having to go through spider, down around the voice coil, and out through the dust cap, it can skip the step of having to go through the narrow annular gap on the inside of voice coil.

    This definitely shouldn't matter as it has the solid felt dust cap.

    Hmm. But you did say that Polk used the holes in the later models which have the more gauzy clothlike dust caps?

    Perhaps they were both designed to help with voice coil cooling by ventilating the airspace above the pole piece better? Cooler pole piece translating to cooler voice coil?

    If the airspace in the enclosure acts as a spring of sorts (esp. with acoustic suspension speakers), perhaps even in a passive radiator or ported speaker it will enable the cone to move more rapidly and respond to transients more quickly.

    Maybe it will effect Vas.

    Those VC holes have zero effect on a felt-cap push-test time....
    The drilling jig is air-tight when woofer is bolted in...
    Took pic before cap completely dried too...
    4suqdstf6yrh.jpg


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  • xschop
    xschop Posts: 5,000
    edited April 2023
    Made another shortened VC spud so I can align and adjust two MWs or glue-in more than one VC at at time. I clearanced the step shorter that holds the VC edge to allow less stress on spider when locked down...


    fdxci9m9mmis.jpg


    jd2agpam1nkw.jpg

    767mhwn1445f.jpg

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  • MrGeology
    MrGeology Posts: 83
    edited April 2023
    Gardenstater wrote: »
    Morning research verifying that Le is very nonlinear and varies with both frequency (I didn't know how much!) and displacement (I did know) of voice coil. Shorting rings are to deal with variation due to displacement, but afaik we don't have that in any of the Polk MWs or tweeters.

    https://www.klippel.de/fileadmin/klippel/Bilder/Know-How/Literature/Papers/Voice_Coil__Impedance_04.pdf

    5ujglgywh8mw.jpg

    Noticed the value measured here is labeled "effective inductance" which varies as the given coil varies in proximity to a magnetic field (speaker magnet). Wondering if this is the reason (or just part of the reason) inductance varies with frequency in a loudspeaker.
    All of the research I did on inductors (grand total of about 2 weeks worth) was specific to winding them at home and reaching intended values, none of which included inductance in a loudspeaker environment.
    At any rate this helped clarify a couple of questions, so thanks for that.
    "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
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  • Gardenstater
    Gardenstater Posts: 4,456
    MrGeology wrote: »
    Gardenstater wrote: »
    Morning research verifying that Le is very nonlinear and varies with both frequency (I didn't know how much!) and displacement (I did know) of voice coil. Shorting rings are to deal with variation due to displacement, but afaik we don't have that in any of the Polk MWs or tweeters.

    https://www.klippel.de/fileadmin/klippel/Bilder/Know-How/Literature/Papers/Voice_Coil__Impedance_04.pdf

    5ujglgywh8mw.jpg

    Noticed the value measured here is labeled "effective inductance" which varies as the given coil varies in proximity to a magnetic field (speaker magnet). Wondering if this is the reason (or just part of the reason) inductance varies with frequency in a loudspeaker.
    All of the research I did on inductors (grand total of about 2 weeks worth) was specific to winding them at home and reaching intended values, none of which included inductance in a loudspeaker environment.
    At any rate this helped clarify a couple of questions, so thanks for that.

    It's all in that paper and in those D'Appolito Equations (showing Le as a function of frequency f). In the paper, Loudspeaker 1 has aluminum shorting ring above the gap and Loudspeaker 2 has one below the gap. The shorting rings act to reduce the inductance at displacements in the direction of the shorting ring location, which will also reduce the impedance.

    elajke4f2w8z.jpg

    6yphc416o6ir.jpg

    5by9je5ypx62.jpg
    George / NJ

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  • Gardenstater
    Gardenstater Posts: 4,456
    Why I don't know. It's over my head. But magnetism is an atomic level phenomenon and has to do with electron orbitals and their spin directions and the like and I think the Le depends upon back EMF generation due to magnetic fields.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
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  • MrGeology
    MrGeology Posts: 83
    Gardenstater wrote: »
    Why I don't know. It's over my head.
    Over my head too, just dabbling really.
    However finally read the paper late last night. From the paper, "the effective inductance is increased as the coil moves away from the pole piece and top plate".
    Reminded me of this article
    http://www.troelsgravesen.dk/coils.htm
    Basically an inductor is, in almost all cases, affected by any surrounding mass, more so when mass is placed directly in the electromagnetic field of the coil (i.e. the open ends of the coil where the magnet plate is located).
    "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
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  • Gardenstater
    Gardenstater Posts: 4,456
    The aluminum plate was worse than the plywood. Not surprising. Aluminum is a paramagnetic material and plywood is totally nonmagnetic.

    https://www.nde-ed.org/Physics/Magnetism/MagneticMatls.xhtml

    "Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and do not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum."
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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    Logitech Squeezebox Touch Streamer w/EDO applet
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  • MrGeology
    MrGeology Posts: 83
    The 6500 with replacement Wuhan coil got here yesterday from @xschop. Here is what DATS turned up for T/S parameters.
    c0q6i674q5l7.jpg
    27yddd4jgrii.jpg
    Ran it through the process half a dozen times with no significant changes.
    The temperature and humidity are pretty high in the shop today, so re-ran the 1980 silver basket MW6500 right afterwards. Today it looks like this.
    xl80xv5362cw.jpg
    32y9wi2n9xbp.jpg
    Other than a high Q(ms) it would appear to be a better match for the other original M7B 6500, in fact a very close match indeed.
    Busy with several things ATM, thought you all might like to see so posted real quick.
    When there is time will be putting it in the original cabinet for side-by-side comparison with the original, then against the 1980 silver basket to determine which will win the M7B permanent residency.
    "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
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    Can you do an overlay of the two impedance curves (maybe you can't because vertical scaling is different)? Zmin is similar although occurring at a lower freq.. Zmax is quite a bit higher and at a lower frequency. Do you have the raw data for each so we could calculate Zavg.? It would be interesting to know the number of turns in each to try to find out why the Sensitivity (@ what freq?) is about 3dB lower. Not surprising that Qms calculated as quite a bit higher according to this:

    r75qax5yno1d.jpg
    Post edited by Gardenstater on
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
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  • xschop
    xschop Posts: 5,000
    Would the slightly lighter coil have anything to do with a higher Qms?
    Don't take experimental gene therapies from known eugenicists.
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  • Gardenstater
    Gardenstater Posts: 4,456
    edited April 2023
    xschop wrote: »
    Would the slightly lighter coil have anything to do with a higher Qms?

    How does DATS calculate Mms, which equals Mmd + Air Load? DATS is saying higher Mms (Mms ratio >1). A more compliant driver with higher moving mass should have a lower Fs, which is what was measured here. Could be the (> than 1) compliance ratio relative to the silver basket is greater than the (< than 1) Mms ratio? Lower Fs actually should give higher Mms, all other things being equal (which they aren't here). (Cms x Mms) must be greater for the Wuhaned driver.

    https://speakerwizard.co.uk/driver-ts-parameters-mmd-mms/

    pjpkvpv3kllm.jpg


    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
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    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
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  • Gardenstater
    Gardenstater Posts: 4,456
    Found another clue. Apparently Cms is proportional to Vas. So for two speakers of approx. equal Vas, Cms is also approximately equal. If the Vas are equal, then the driver with the lower Fs would have to have a higher Mms.

    c9uejiqnxinv.jpg
    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
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    Custom Steve Wilson 1m UPOCC Interconnect
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  • Gardenstater
    Gardenstater Posts: 4,456
    The rest of the pieces of the puzzle are here in the formulas given:

    https://audiojudgement.com/thiele-small-parameters-equations/

    sc7ynto28mhf.jpg
    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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  • xschop
    xschop Posts: 5,000
    So a set of M10 6510 MW's leaves the Polk factory 40 years ago and your kid in college, pounds them into oblivion at the dorm. They have higher Vas when their suspensions are about wore out?
    Don't take experimental gene therapies from known eugenicists.
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  • Gardenstater
    Gardenstater Posts: 4,456
    Yeah and the voice coil is probably rubbing too, especially if it is a MW6500 in a 7B 🤣

    Turns out DATS has a patented method of checking for VC rubbing, I found out today. Fs shouldn't shift as level decreases during impedance testing, unless there is a damaged driver:

    4ayuz9fb1ikm.jpg

    9ly8fpr9vjis.jpg


    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
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    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • MrGeology
    MrGeology Posts: 83
    Gardenstater wrote: »
    Can you do an overlay of the two impedance curves (maybe you can't because vertical scaling is different)?
    Have not yet figured out how to get DATS to do an overlay, should be a simple thing but has eluded me thus far.
    Gardenstater wrote: »
    Zmin is similar although occurring at a lower freq.. Zmax is quite a bit higher and at a lower frequency. Do you have the raw data for each so we could calculate Zavg.
    Was in such a hurry (currently working on an M7 Series 2 refurb) didn't even look at the Zmax or impedance curve scaling differences until you pointed them out. Not sure what raw data is or where to pull it from, will look into it.
    Gardenstater wrote: »
    It would be interesting to know the number of turns in each to try to find out why the Sensitivity (@ what freq?) is about 3dB lower.
    The Sensitivity is 3dB low compared to the 1980 MW6500, but compared to the other (original) 1983 MW6500 it is only 1.16DB low. Will try to re-run the original and the Wuhaned through DATS in a short time period such that temp/humidity can be ruled out as contributing factors to T/S discrepancies. Should be this week sometime.
    "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
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  • MrGeology
    MrGeology Posts: 83
    edited April 2023
    Assembled a bunch of data (T/S Parameters and M7B cabinet sweeps) split into two new posts,
    here:
    https://forum.polkaudio.com/discussion/198508/mw6500-dats-t-s-parameters-revised-pics
    and here
    https://forum.polkaudio.com/discussion/198509/m7b-dats-cabinet-impedance-sweeps-pics

    Edit: forum seems to have temporarily pulled those posts pending "approval". Will repost them tomorrow if they aren't up by then.
    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
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  • Jazzhead
    Jazzhead Posts: 533
    xschop wrote: »
    So a set of M10 6510 MW's leaves the Polk factory 40 years ago and your kid in college, pounds them into oblivion at the dorm. They have higher Vas when their suspensions are about wore out?

    aosv8212q56d.png
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  • xschop
    xschop Posts: 5,000
    MrGeology wrote: »
    Assembled a bunch of data (T/S Parameters and M7B cabinet sweeps) split into two new posts,
    here:
    https://forum.polkaudio.com/discussion/198508/mw6500-dats-t-s-parameters-revised-pics
    and here
    https://forum.polkaudio.com/discussion/198509/m7b-dats-cabinet-impedance-sweeps-pics

    Edit: forum seems to have temporarily pulled those posts pending "approval". Will repost them tomorrow if they aren't up by then.

    Somebody have something to hide?
    Don't take experimental gene therapies from known eugenicists.
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