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: 45,638
    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?
    Political Correctness'.........defined

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  • Jstas
    Jstas Posts: 14,263

    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.
    Expert Moron Extraordinaire

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  • billbillw
    billbillw Posts: 5,895
    My guess would be someone cooked the voice-coil in that tweeter.
    Main 2-ch:
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