Very Rare db6520 tweeter dull

Scored a set of super rare Polk db6520 from the 90's but after setting them up I noticed one was fairly dull compared to the other (which sounds VERY nice btw) when fading right into each speaker on my HU.

I tried swapping speakers on a different channel and exact same result so I knew it was the speaker itself.

So I was thinking it was a bad capacitor and ordered a pair of Jantzen 450uf 400v "Cross-Caps" (which is the same specs as the Bennic one on the speaker), but after I replaced the suspect capacitor and left the cap in the other good speaker to compare the results I found the sound to still be dull, although the sound definitely improved ALOT it still had the exact same dullness to it compared to the good speaker. Thinking it could be possible but unlikely a break in period for the cap, I have left it a few days of random playing music and the sound has not changed, usually new caps will just sound a bit harsh but not lower in sound.

Anyway so I am guessing now it has to be something wrong with the tweeter itself as all the connections looked fine on the back of the speaker when I did the cap, and I only suspect the tweeter as the mids appear to be coming out fine.

Could it be Ferrofluid need replacing? I will be taking them out of the car to put them on my work bench tomorrow and I can do a test on the tweeter wires with a DMM. Im guessing that if this gives correct Ohms that Ferrofluid is most likely the problem. I really need to get these speakers back in action if I can, any advice/ help would be greatly appreciated!


  • F1nut
    F1nut Posts: 49,968
    Must be rare as there's basically no info on them out there. I found this though, but not much help for your situation I'm afraid.

    Are you sure the tweeter used ferro-fluid or is that a guess?
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  • Jstas
    Jstas Posts: 14,741

    That's not how ferro fluid cooling works.

    Additionally, you cannot just replace ferro fluid.

    Replacing a cap may have a "break-in" period but it should have changed something. If nothing changed, the capacitor wasn't the problem.

    If your tweeter sounds "muted", it's either a component of the high pass filter network other than the capacitor you replaced that is bad or the tweeter itself. Another possibility is a broken connection somewhere. You can use a digital multi-meter to test for continuity across the woofer, tweeter and high pass filter components.

    If you are going to use a digital multi-meter to test the tweeter then you need to test for continuity first. If it shows open, your tweeter is bad, the speaker is junk because nobody replaces tweeters on coaxial speakers. If the tweeter shows continuity then you next need to test the resistance/impedance. But verifying that is hard to do because specs for the dB6520 are pretty much non-existent. So there's no way to tell if the speaker is within spec or not because you don't know what the original spec was.

    I don't know how the dB6520 is wired, though, so if you cut the tweeter out, you run a chance of creating an open circuit depending on how it's wired. If it's wired in parallel, it'll be fine. Wired in series, the woofer won't work because the circuit is open. It's likely parallel. However, if you by-pass/cut out the tweeters and try to use the woofers as woofers in a component set and they have an impedance too low for the crossover network you use to handle, you will burn up the crossover network. If the impedance is too high, it will change how the crossover network behaves and affect sound.
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  • billbillw
    billbillw Posts: 6,289
    My guess would be someone cooked the voice-coil in that tweeter.
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  • PoweredByDodge
    PoweredByDodge Posts: 4,185
    edited August 2021
    John, when are you going to do something other than sit in this forum and talk to the mindless? I digress... the DB series (original DB series - Polk's flagship mobile speaker at the time) had a 5.25 mid with a silk dome tweeter, or a 6.5 mid with the same tweeter, and same outboard crossovers. I had a pair of these in my then girlfriend's car. They were big pimpin. And needed something in the neighborhood of 75 watts per channel to get moving. Fast forward, the DX series that replaced them were basically the same speaker, with what I would say were some cost-saving measures (call it a 'mid-product life refresh'). The original Polk MOMO series components that replaced the DB/DX as Polk's top of the line were basically beefed up DB's. They un-did the economization that was done to the DX and then went further and made them even better (improved upon the design). All 3 of these products were evolutions of Polk's 'Dynamic Balance Technology' (their way of building a speaker, and the origin of the 'DB' name). Fast forward some more to like... I dunno... 2003 / 2005 ? The Polk "DB" speakers were re-launched, with a slightly altered name - lowercase now, "db". They were nothing like their predecessors (IMHO), and were only marginally better than the Polk EX II and EX III speakers of the earlier era. I have a set in my '76 Cadillac's rear deck, from 2006 (I think I bought them 'new old stock' on evil-Bay at the time), and some MB Quart 3.5 inch in the front dash (because nobody made a decent 3.5 at the time, and now I'm too lazy to change them out). It all still works, although I ripped the two 8 inch subs out of the rear, and slammed two 500-watt 10's in there now, running on an MTX81000D that was collecting dust for just such an occasion. Just did that project a few months ago.

    To answer you're question - they're 21+ year old car speakers... they're not going to last forever. UV damage, overdriving, humidity, or god knows what may have destroyed them. Move on sir, move on.

    Finally - it's really nice to see that after not having posted in this forum in over a decade, nothing has changed - folks still think wires "burn in" and capacitors need to "break in". I'm going to go to my grave with that sad thought in my mind. Speakers however - they do need to break in - at least large / heavy ones. The two IDMax 10's (they're on 'version 4' now) that I put in my 2-door standard cab Silverado (yes, I said "2 door", "standard cab", "Silverado" and "two IDMax 10's" all in the same sentence) needed quite some time to loosen up --- like no ****, months and months. I would pound em, they'd sound funny, I'd pound em harder, sound funny. After about 6 months that went away. Now they just cause erratic heartbeat and headaches - like they're supposed to.
    The Artist formerly known as PoweredByDodge
  • PoweredByDodge
    I just left a flippin comment here and it was removed. FTW.
    The Artist formerly known as PoweredByDodge
  • PoweredByDodge
    John Stasny ... Still leaving 3 page responses after all this time. Love it.
    The Artist formerly known as PoweredByDodge