Help diagnosing woofer distortion on Original Large Advents

Discussion in 'Speakers' started by Onebean, Mar 20, 2017.

  1. Onebean

    Onebean AK Subscriber Subscriber

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    Location:
    Nebraska
    Yep, that's right I've got one of 4 speakers with an issue. Many of you reading this likely saw my post about collecting 2 sets of these in under 2 weeks recently, and my honeymoon phase. I noticed a couple days ago, that some distortion was present in the left channel. It sounded like a tube was going bad in my phono pre, and I was busy playing with set up and a building new stands for my OLA stack. Last night I swapped tubes in my phono pre, and no change. Then I pulled the phono pre completely, and ran off the phono stage in my Yamaha C-85, resulting in no change. Still the same distortion. So I thought maybe the step up transformer I just added was the problem. I removed that and there was no change, still distortion. So I thought maybe something happen to my amp, or I had a bad cable. I swapped the right and left RCA'a on the amp and the distortion stayed on the left. I was able to isolate it to the bottom set, and it was the left speaker only.

    The problem is distortion while the music is playing. I can still hear sound from that woofer, but it also has a distorted sound.

    The guy who I bought them from replaced the surrounds. Do you think he got it off center and the voice coil is rubbing? I don't know what a rubbing voice coil sounds like under power. Is it a cross over issue? What's a fair price for a used masonite driver? I'm temped to buy a used driver if I can find one for a fair price, and swap it out. Let me know what you think.

    As for re-capping, I don't want to open a can of worms, but should I recap and re-resistor these guys? Is there a cap that will improve the sound quality? I've read that paper in oil makes a big difference. Anyone care to share their recapping experience?

    Onebean
     
  2. onplane

    onplane What! No Wake???

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    Onebean, before you do any thing, you have one more test to conduct. You said you switched the rca's and the distortion stayed on the left speaker. That means the source of the distortion is not in the left pre-amp.

    Now we need to test the left power amp. The way you do that is switch the left and right speaker outputs on your power amp.

    If the problem (distortion) moves to the right channel, the source is in your left power amp. If distortion remains on the left channel, then it's the Advent woofer.

    Regards,
    Jerry
     
  3. Onebean

    Onebean AK Subscriber Subscriber

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    Good call Jerry. I'll check that tomorrow. Thanks.

    Honestly, I hope it's the speaker and not the amp.
     
  4. westend

    westend Audiopile

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    Probably a failing component in the crossover network.
     
  5. Tim D

    Tim D AK Subscriber Subscriber

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    Let us know how your test turns out. If it isn't in the power amp, then we can take next steps to see if it is the woofer or crossover.
     
    Onebean likes this.
  6. Onebean

    Onebean AK Subscriber Subscriber

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    I quickly swapped in my set of ADS L-880's at lunch, and the distortion was gone. It seems to be related to the speaker. How should I determine if it's the speaker or cross over?
     
  7. Tim D

    Tim D AK Subscriber Subscriber

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    Swap it back and monitor for a occurrence in the problem. It'll be hard to diagnose if it isn't misbehaving.
     
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  8. gtv2000

    gtv2000 AK Subscriber Subscriber

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    you can check for voice coil run by pressing the woofer in by hand (maybe 1/4 or 3/8 inch). if it doesn't rub, It's easy enough to swap the woofers between cabinets to check if it follows the speaker or the crossover, eight screws and two spade leads. There's not much in the crossover that would cause distortion in the woofer - usually just an inductor in series.
     
  9. Onebean

    Onebean AK Subscriber Subscriber

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    Ok, I'll do that. I don't understand which component does what in the cross over, but I assumed the 10" runs basically full range, with a component cutting out the highs. That's why I assumed it was a driver issue. If the voice coil is rubbing, is the woofer ruined? What else could go wrong with the woofer?
     
  10. gtv2000

    gtv2000 AK Subscriber Subscriber

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    You could try refoaming the woofer - could be it just got off-center by a bad refoaming job. Of the spider could be damaged, causing a lack of support. If it works at all the electricals are probably okay I would think. Who knows? Just a thought, you could try rotating the woofer 180 degrees - the spider may have sagged. not sure if that would be a good permanent fix.
     
  11. ducati2

    ducati2 AK Subscriber Subscriber

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    I had the same problem with the same model advent speaker that was recently refoamed. I refoamed it again and the sound went away. I bet this is your problem, off center refoam job. HOWEVER, before I would do a refoam, I would simply swap the woofers from the cabinets and that would nail down whether it is a woofer or your crossover.
     
    stereoguy70 likes this.
  12. drumbum

    drumbum Well-Known Member

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    I recommend shimming on all refoams, unless you can't, like a PhaseTech solid piston driver.
     
    Old Guy8 likes this.
  13. Onebean

    Onebean AK Subscriber Subscriber

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    After some diagnostics I have determined the woofer was reckoned off center. I seems to be barely rubbing, and causing the distortion. I got around the issue by rotating the speaker 180 degrees. Gravity has just enough pull on the cone to cure the rubbing voicecoil. I'll likely reform it in the future, but for now the problem is under control. Thanks for all the help.
     
    gtv2000 likes this.
  14. wmgwizard

    wmgwizard AK Subscriber Subscriber

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    Another very important thing to remember with the OLA or any sealed/bass reflex speaker is sealing the drivers and enclosure.

    Make sure to use some sort of gasket around the drivers whenever you remove/replace them. Small air leaks have a large impact.

    IIRC there is just a single capacitor in the OLA, fairly easy and inexpensive to update. The existing electrolytic capacitor can be replaced with another electrolytic or updated/upgraded with a polypropylene cap. Dayton and Solen make reasonably priced poly caps. You can spend more but the Advent "fried egg" tweeter is only so good.

    The capacitor actually blocks low frequency sound from reaching the tweeter. Think of it almost like a sound valve. The low frequency we the tweeter couldn't reproduce anyway are blocked while the higher frequencies that it can pass through.

    A coil does the opposite for the signal by reducing the higher frequency information from the signal path.

    Various combinations of caps and coils can be used to make fairly intricate crossovers, a "black art" if there ever was one.
     
  15. Onebean

    Onebean AK Subscriber Subscriber

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    Wizard, thanks for the explanation. The drivers are sealed in my cabinets with a tacky moldable substance.

    What purpose do the resistors serve? Level matching the drivers?
     
  16. KingBubba

    KingBubba "Too Much Stuff" Subscriber

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    Chances are that the spyder has developed a sag over the years and your 180 deg move settled the issue. Leave it be now because it ain't broke no more. If the issue rears it's ugly head again, then do a refoam to see if that helps. If it does not help, it will be time to look for a new woofer.
     
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  17. wmgwizard

    wmgwizard AK Subscriber Subscriber

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    Many tweeters are more efficient than the corresponding woofer and the resistor can be used to help reduce the tweeter output.

    There are other uses for resistors in crossovers as well though. As I eluded to before, crossovers can be fairly simple or diabolically complex devices. They are a subject all their own.
     
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