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  • PA speaker not working - What/How to test components?

    Hi everyone. I've got a couple of cheapo 15" passive PA speakers that I use for small acoustic gigs. The woofer stopped working on one of them. I've got the cabinet opened up, and I've tried to look up info on what/how to test components. The only thing I've seen on testing a woofer is the 9V battery pop test, and testing impedance. It's an 8 ohm speaker, yet the measurement I get is 8.8 ohms! I don't know what that means, or what to do next. Could the crossover be bad? I don't know how to test that, either.

    Kinda lost here at this point. Any help would be appreciated.


  • #2

         Speaker repair is not as easy as it sounds.

      The chances are the cost of the parts to fix the speaker may exceed the speakers value.

     

    How to test with a volt/ohm meter (this will give you some guidance on good and bad ohm readings)
    http://www.youtube.com/watch?v=gTIjFJWh0_E

     

    A good site with pictures  and descriptions of various speaker problems:
    http://sound.westhost.com/articles/speaker-failure.html

    An actual repair of a speaker:

    http://www.youtube.com/user/simplyspeakers/videos

     

    An easy to read instruction diagram for testing ohms:

    http://www.wikihow.com/Measure-Speaker-Impedance

     

    An example of speaker repair parts and prices:

    http://www.parts-express.com/

    Comment


    • #3
      You have determined that the speaker's voice coil has not friend and that the speaker itself is probably (but not necessarily) okay, assuming your problem symptom is "it doesn't work" as opposed to "it sounds funny".

      Next you need to test the crossover, specifically the low-pass side. I don't know a good general test for this so I'll refrain from commenting.

      Wes
      <div class="signaturecontainer">--<br><br>Hammond: BC, M3, Split L111, L122 / Leslie: 51, 760 / Yamaha: DGX-620, PF-85<br><br>Follow my new band, <a href="http://DrBombay.ca/connect.html" target="_blank">Dr. Bombay</a>! We're going to be organasmic!</div>

      Comment


      • jmo1112
        jmo1112 commented
        Editing a comment
        Thanks for your help so far. Unfortunately, happywith12strin, I've already seen those links you posted, and they got me to this point. Maybe someone who knows proper crossover testing will be able to chime in.

    • #4

       8.8 ohms is too high jmo...it should be about 5 or so.

      Comment


      • agedhorse
        agedhorse commented
        Editing a comment

        Have you tried the 9v battery test on the woofer itself disconnected from the crossover? (Note which wire goes to which terminal before taking them off.


    • #5
      If HIS lpf has series caps, I think we may have identified the problem...

      Comment


      • jmo1112
        jmo1112 commented
        Editing a comment

        I did get the woofer disconnected from the crossover.  I connected my amp directly to the terminals, and I get the same result... a very thin, tinny sound, with basically no bass.  I also tried reconnecting everything back to the crossover, just to see if anything changed, and it did not.  While the woofer was connected directly to the amp, I used a test tone app on my phone to send signal.  I can hear the tone down to 100Hz (though not very strong or loud). The level of the tone increases considerably around 320Hz, and stays at roughly the same level once I get to about 800k.

         

        Gonna attempt to attach a video of music playing directly through the woofer, and also a pic of my crossover.

         

        IMG\_4968.JPG

        Attached Files

    • #6
      If the cone doesn't move, it didn't overheat. The pole piece broke loose from the back plate and is stuck tight to the return side of the gap pinching the voice coil tight. It's a common failure in cheap, junky drivers. It's not repairable, you will need to source a proper replacement.

      The crossover is what it is. Matches the rest of the speaker just about right. It's not IMO worth putting any real money into those speakers.

      Then again, what do I know. You were the one trying to convince us that you knew a lot more than you did eh?

      Comment


      • #7
        So, Agedhorse, you're giving a +1 vote for garbage, yes?

        And I don't know what post I've made would lead you to believe that I was trying to convince you guys I knew more than I did. Thought I made it clear that I did not have much knowledge at all on this subject. You may have me confused with the guy doing the SPL measurements in his living room or something.

        Comment


        • Craig Vecchione
          Craig Vecchione commented
          Editing a comment

          I'm pretty sure Andy had you confused with jamesb who was arguing several points with him.


          Regarding your speaker, the woofer is toast, so your options are to either trash the speaker or find a suitable replacement woofer. A quick search shows that USSpeaker has an Eminence Alpha 15A for $65. They're a reputable retailer, Eminence is a solid mfg., and that's about a cheap as you'll find for a new 15" driver. There's no guarantee the driver is a perfect match to the cabinet (in audio terms; the speaker will fit the hole), and may sound a little different than the other working box. But if it sounds decent, you have the option of replacing the other driver in the working box so they match.


          You can of course look for used speakers, but for the same reasons I stated above, you should get two of whatever you find. And of course test them before money changes hands. The troubleshooting you just did is what you would do to test a candidate for purchase...


      • #8
        Jmo, I'm sorry, I confused you with jamesb. Please accept my apology.

        It looks like a Chinese cast frame driver, we have seen problems where adhesive used has failed with the heavy ceramic magnets and poor pieces.

        What brand and model is your cabinet? I might be able to locate a suitable replacement for you.

        Comment


        • jmo1112
          jmo1112 commented
          Editing a comment

          Apology accepted!

           

          I honestly don't know the brand.  They were bought about 10 years ago from a struggling local music store that could no longer get respectable vendors.  So we got a couple of nameless speakers from them for a rehearsal space that I started using for bar gigs. They literally just say ABS 15 on the back, and then 300W RMS and 8 ohm.

          The Eminence route might be an option...that's certainly not a terrible price at all, but I would need to buy 2.  Should I replace other components?  I have no idea what the cost of replacing crossover components would be.  I realize it's a cheap box, and this may just be polishing a turd, but I figure it's worth asking.

           

          I have a couple Yamaha BR12m's and a JBL MP212 that I used for monitors.  Those can certainly get me by if they have to.  I honestly just didn't think they sounded as good as my cheap Chinese speakers. 

           

          This, if nothing else, has been very educational. 


      • #9
        I live in Memphis. I'll try to get a pic of it in the morning. It's 20 degrees out right now.

        In an effort to not make myself look foolish, 15's are not good for mains? I mean, I know a 3-way is better (but not really an option for me), but 15's are bad? Is that like the pro audio's marketing plan to sell bigger is better (and more expensive) to people who don't know better?

        When I use my ears, the 15's sound better. Clearly that could due to comparing them to crappy 12's, but nonetheless, they do.

        Comment


        • #10
          15's can be just fine for mains. Smaller speakers can work just as well or even better when used with subs.

          Comment


          • jmo1112
            jmo1112 commented
            Editing a comment

            You know, I'm probably just not gonna fool with it.  They're cheap, heavy, and have lasted me almost 10 years.  I guess they put they did what they were supposed to do.  Thanks for the help on this.

             

            Gonna start a new thread for speaker recommendations, I suppose.

             

             

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