6500 anomaly
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Yep, that is certainly better than an explanation lol"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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.
George / NJ
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I thought edge winding came along much later than the mw6500 was used.
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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
Crown D150 amp
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iPurifier3
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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 -
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.
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.
Don't take experimental gene therapies from known eugenicists. -
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
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 -
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...
Don't take experimental gene therapies from known eugenicists. -
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. -
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.
Don't take experimental gene therapies from known eugenicists. -
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
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 -
@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.
Don't take experimental gene therapies from known eugenicists. -
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
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 -
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.
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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
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 -
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.
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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
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 -
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.
Post edited by xschop onDon't take experimental gene therapies from known eugenicists. -
If anyone has blown-coil 6511's, these would be good to drop in...
https://www.ebay.com/itm/403977486301?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=szdlj9svski&sssrc=2349624&ssuid=US22loU_QhS&var=&widget_ver=artemis&media=COPY
Don't take experimental gene therapies from known eugenicists. -
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.
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!
"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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
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 -
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. -
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
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 -
Gardenstater wrote: »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."They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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.
Post edited by MrGeology on"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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.
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.
Temperature in workshop feels maybe 5 degrees cooler today than first day it was run.
"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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
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 -
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. -
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.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?
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?
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).
"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States -
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...
Don't take experimental gene therapies from known eugenicists. -
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.
Same inductor with DATS.
The 1980 MW 6500 on LCR.
The 1980 MW 6500 on DATS (Free-Air only, no VAS measurement).
"They’re not after me, they’re after you… I’m just standing in the way!” -Donald J. Trump, 45th President of the United States
