can ultra-low frequencies damage speakers or sub?

Discussion in 'Speakers & Subwoofers' started by BurkeP, Aug 8, 2003.

  1. BurkeP

    BurkeP Extra

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    I put together a CD with a bunch of different tones and sweeps to test speakers and subwoofers (and more fun - love those 150-20hz sweeps!) and was wondering if playing as low as 10hz might damage speakers or subs in any way?

    Thanks.
     
  2. BurkeP

    BurkeP Extra

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    And if you have any suggestions for fun multi-tone sweeps, let me know.
     
  3. JessPrice

    JessPrice Stunt Coordinator

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    I think to create a frequency an octave lower at the same dB (say 20hz to 10hz) it requires 4x the excursion, I may be wrong, but if your sub is reaching it's maximum excursion at 20hz, you better not push it to play 10hz at the same dB.
     
  4. BurkeP

    BurkeP Extra

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    What if I just play a 10Hz tone through a pair of regular speakers? Not necessarily trying to hit any particular dB's, just playing it at moderate volume to see what comes out. Presumably nothing, but will it damage the speakers to put this signal through them?
     
  5. Dan Hine

    Dan Hine Screenwriter

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    As long as you are playing it at a low enough level that the driver does not pass it's excursion limits then no, it will not damage them. BUT, be aware that you will not be able to hear it so don't keep turning it up assuming that you are still safe. Chances are a pair of "regular" speakers will not be able to play back a 10hz tone anyway. So don't bother.
     
  6. JessPrice

    JessPrice Stunt Coordinator

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    I doubt the regular speakers will barely even move at 10hz if you have a high pass crossover on them set at around 80hz or so. If you have a subsonic filter on your sub, make sure it is set higher than usual if you plan on playing that 10 hz tone with a good amount of power.
     
  7. Michael R Price

    Michael R Price Screenwriter

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    I'm under the impression that most regular speakers, including mine, have such a short Xmax compared to what the suspension can handle without bottoming, that it is nearly impossible to damage them from over-excursion... the motor simply can't push the cone back and forth far enough to hurt itself (and you get major distortion). In my speakers the Xmax is about 5mm each way and the Xmech (before bottoming) is 13mm. With subwoofers it is a different story.
     
  8. Matt_Doug

    Matt_Doug Stunt Coordinator

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    I believe one of the guys at SVS in another thread mentioned that pure sine wave tones do damage to speaker voice coils. make sure your tones are logarithmic.
     
  9. ChrisWiggles

    ChrisWiggles Producer

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  10. Randall Duncan

    Randall Duncan Stunt Coordinator

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  11. ChrisWiggles

    ChrisWiggles Producer

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    Music is just a continuous mess of sine waves. A single sine wave is the easiest thing to reproduce. It's the natural motion of the drivers, no dc current, no clipping. I don't see how you'd overheat anything doing that. The danger would lie in your not being able to judge the volume very well of a single tone, and thus overdriving your speakers without realizing.

    And i right?

    And what is a "logarithmic tone"?
     
  12. Michael R Price

    Michael R Price Screenwriter

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    Power is power. A woofer doesn't care if you give it a sine wave or a sine sweep or a clipped mess.
     
  13. Chu Gai

    Chu Gai Lead Actor

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    There's no definite answers but a very strong maybe makes the most sense. Woofers typically die from mechanical failure and that can come from a variety of means. This will happen if the woofer is driven so hard at a particular frequency that the voice coil knocks into the rear of the magnet or even jumps out of the gap and winds up jamming trying to go back in. Ooops!
    The amount that a woofer moves is related to the inverse square of the frequency for a given input (sine wave). So some typical excursions would be...

    80 Hz 1/16"
    40 Hz 1/4"
    20 Hz 1"
    10 Hz 4"

    High quality drivers have a maximum excursion of about 1/4" and if you try to make it move an inch, you'll probably kill it. Try making it move 4" and you'll be hoping the manufacturer will send you a replacement woofer.

    Although speakers have specifications like power handling capacity, this is the power handling capacity for music. Music is most certainly not sine waves and it's energy distribution is very roughly approximated by 1/f. In other words, less musical energy at the higher frequencies. So if your speakers state they have a power handling of 200 watts, and you take a HF signal and feed it to your tweeter at say 100 watts (likely even less), you'll fry your tweeter. Send a low transient to your woofer and it could only be 10 or 20 watts, and you'll kill it.

    If you're going to do this, its at your own risk and you should excercise enormous care.
     
  14. MingL

    MingL Stunt Coordinator

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    Yes, pure sine tones at low freq can kill the woofer if the volume level is loud enough.

    The fatality is not instantaneous but the damage takes some time into the sine wave before the damage is irreversible.What damage? The VCs get so hot that the enamel coating (esp on cheaper drivers) on the VCs can melt and permanently short circuit the VCs. This happens upon abusing the driver with 10hz tones driving at high volumes for extened periods of time.
     
  15. Michael R Price

    Michael R Price Screenwriter

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    Don't long excursions help to cool the voice coil by moving it quickly through the air?

    ...I still think most normal speakers have too little Xmag relative to their Xmech, for over-excursion to be of any danger.
     
  16. ChrisWiggles

    ChrisWiggles Producer

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    What are you guys talking about? All music is sine waves. Just lots of them all jumbled together.

    [​IMG]

    The easiest thing for a driver to do is a single sine wave.
     
  17. Chu Gai

    Chu Gai Lead Actor

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    yes Chris, but we're talking one particular frequency, well below the capablities of a woofer, being reproduced at some arbitrary power. and fwiw, the typical failure mechanism of woofers is mechanical while that for tweeters is largely heat related.
     
  18. Randall Duncan

    Randall Duncan Stunt Coordinator

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  19. ChrisWiggles

    ChrisWiggles Producer

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    Sure it's correct. That's what music is, is a massive conflagration of individual tones.

    These tones are sinewaves at a particulat frequency.

    Obviously playing a very low tone on a speaker not designed to handle that amount of power, and at loud volumes can cause different kinds of damage, both from too much excursion, and VC overheating. Just because it's a sine wave though, that poses no threat to anything.

    A 400 hz sinewave is easily handled my most woofers, and it could do that all day and not break a sweat, if it's halfway decent, and not at too loud a volume (and not clipping, which would then damage the tweeter instead.)
     
  20. Chu Gai

    Chu Gai Lead Actor

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    400 Hz yes, but the poster was curious about 10 Hz. well if you can find an undampened, springy old turntable, put on your favorite LP, crank up the volume a bit, and then jump around.
    Randall, Chris is entirely correct that music can be considered a mixture of sine waves of various frequencies, amplitudes, durations, etc. It's commonly called the law of superposition and this is why something like fourier transform mathematics can be used to express musical notes. google search might turn up some useful information along those lines.
     

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