Subwoofer making horrible grinding noise

Davemusic
Davemusic Posts: 4
edited May 2003 in Troubleshooting
Hello
One of my 4yr old RT1000PBLK's is not happy. Actually, the main drivers still are fine, but all of a sudden the sub is crazy. The sound is a constant griding with no relation to what is going through the speaker. In fact, the noise continues when the music is turned off. I have to unplug the speaker(sub) to shut it off. I can plug it back in and it is quiet until a signal is fed to the speaker again. I tried replacing the small fuse inside but it made no difference. Appreciate any help/suggestions. Thanks.

Dave
davidmartin.org
Post edited by Davemusic on
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Comments

  • mantis
    mantis Posts: 17,194
    edited May 2003
    Thats a very strange problem your having.....I assume the driver is blown but that doesn't explain why it continues to grind as you put it.....

    Do both subs do it?meaning left and right?or is it just one of them???

    All I can say here is that I owned the same speakers and had a problem with one of the subs .

    For the hell of it,take the plate amp out,and tighten up the screws holding the woofer.They could have came loose.Could be that simple but I'm guessing on a bad driver.

    Call polk if this doesn't help.
    Dan
    Dan
    My personal quest is to save to world of bad audio, one thread at a time.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited May 2003
    Bad amp - sound is called "motor boating". Brett or HBomb or Tour2 can tell you what it actually is doing, electronically.

    Pulling the fuse or the plug kills the sound, and the sound is a constant noise right?

    Time for a new amp - Polk will make it right. Swap out is easy.

    Doc
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • mantis
    mantis Posts: 17,194
    edited May 2003
    Intresting.......

    bad amp with a name of "motor boating" huh...I'd like to learn more about this theory.
    Dan
    My personal quest is to save to world of bad audio, one thread at a time.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited May 2003
    Yep, not all amps die quietly. Sometimes a transistor (or whatever) goes bad, and the amp simply starts making a constant farting or warbling noise, and the nickname for it is "motor boating".

    I've read about it over at HTF a few times. One guy with powered towers had the cops break down his door and shut off his system because it happened to him and he was gone for a long weekend and his apartment neighbors were going bonkers.

    Doc
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • Davemusic
    Davemusic Posts: 4
    edited May 2003
    Well,
    Motor boating is certainly a good description. Thanks for the replys guys. Yes, when the fuse is pulled the sound is gone. Replace the fuse and plug in and it is quiet till you send a signal again. Volume of music makes no difference either. Guess I'll give Polk a call tommorrow. Have a good holiday guys!


    Dave
    davidmartin.org
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  • burdette
    burdette Posts: 1,194
    edited May 2003
    Motor boating is the amplifier going into an unstable low-frequency oscillation mode. You're getting positive feedback into the input. It stops when the amp is shut down, doesn't start at power up, but starts when the amp is fed a signal - the amp tries to amplify, and goes into the unstable oscillation. That is why once it starts the input signal is no longer relevant, and why the noise is rhythmic.

    Slight chance it is connections or a bad connector. I'd pull everything apart, clean it and reconnect. Couldn't hurt. You could do this in the internal wiring for the amp and driver as well.

    Could be the isolation capacitors... they are no longer... capactitating.

    The amplifier itself *may be* fine.. this is fundamentally an isolation problem, i.e. lack of isolation gets the oscillation going. The amplifier is still amplifying.. just not the proper signal.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited May 2003
    Originally posted by burdette
    Motor boating is the amplifier going into an unstable low-frequency oscillation mode. You're getting positive feedback into the input. It stops when the amp is shut down, doesn't start at power up, but starts when the amp is fed a signal - the amp tries to amplify, and goes into the unstable oscillation. That is why once it starts the input signal is no longer relevant, and why the noise is rhythmic.

    Slight chance it is connections or a bad connector. I'd pull everything apart, clean it and reconnect. Couldn't hurt. You could do this in the internal wiring for the amp and driver as well.

    Could be the isolation capacitors... they are no longer... capactitating.

    The amplifier itself *may be* fine.. this is fundamentally an isolation problem, i.e. lack of isolation gets the oscillation going. The amplifier is still amplifying.. just not the proper signal.

    I KNEW an EE would come to my rescue! Thanks for the better description.

    Doc
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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