Need Help Troubleshooting Polk 7

I have a pair of early Polk 7s: Peerless tweeters, single fuses on back. One of the speakers works flawlessly. But the other one exhibits an irregular break-up of high frequencies. Seems like it needs a certain combo of freq and volume to occur. It's not a drop out of sound, but more like a raspy sound or distortion in audio quality.

It's hard to replicate, but something is not right. Sometimes I find myself thinking it healed itself, only to find that it reappears. I've switched channels, tried diff amps, and different sources.

Just looking for some thoughts on where to look, or what it might be. I was first going to clean the connections at the binding posts, fuses, and drivers. Anything else to check/clean?

I always thought these Peerless tweeters either worked or they didn't. Is it possible it could be an internal problem with the tweeter?

Thanks, in advance, for any suggestions!

Comments

  • pitdogg2
    pitdogg2 Posts: 19,473
    edited August 2020
    I was first going to clean the connections at the binding posts, fuses, and drivers. Anything else to check/clean?
    I'd start with that thought


    I bet the wire is corroded at the fuse block as well
  • Gardenstater
    Gardenstater Posts: 2,021
    My fuse wires are thoroughly sealed with gobs of hotmelt on the inside of the cups. I have no clue what the attachments of the wires to the fuse block look like but I will soon find out when I put Cardas Binding Posts in and 11.5 gauge Cardas Litz. My Peerless tweeters were soldered but if yours have fastons you could check and clean those connections as well. If they do have fastons it should be relatively simple to swap the tweeters and see if the problem stays with the speaker or follows the tweeter. If you want to switch to fastons and do the experiment anyway, you may have to be careful like I did and cut the tweeter wires about 1 in. from the tweeter and put on a male faston on that wire and a female faston on the wire coming from the crossover. Gold plated brass ones (at least for the females) are available from the Auto Parts stores. I think it's Dorman brand and I forget if it was PepDudes, Advance, or Autozone that I found them. For the tweeters the proper size is 7/64" (2.8mm). You can get some overpriced ones from Partsconnexion.com The WBT's.

    To clean the fuseholders and other connections, 2000 grit paper works well. Or did I use 3000? Either one is fine.
    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
  • Well, turned out to be the tweeter. I switched them between boxes, and the problem went with the driver. Then, I replaced the bad one with a known good one from my stash... That fixed it!

    I threw a DVM on the bad one and got 8.8 ohms. I used to think I could verify a good one by checking ohms. But this seems to indicate ohm check alone is no guarantee it's a good one.
  • Gardenstater
    Gardenstater Posts: 2,021
    Nice and congratulations! Could've been a rubbing voice coil. We can't really check them very easily manually although I was able to tell visually that one of the ones I was working on was shifted due to some impact in shipping. I had to loosen the 4 screws and realign the voice coil by making careful precise movements in all 4 of the possible directions with metal shims in a jig allowing me to control it all. I determined the best position by the highest dB reading while playing a 5kHz tone. When I was sure I had it aligned as best I could, I used Loctite on the screws.
    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