Woofer gunshot! ;)

Discussion in 'Speakers & Subwoofers' started by Kaj, Jul 15, 2004.

  1. Kaj

    Kaj Stunt Coordinator

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    Hi,

    I got a second Velodyne subwoofer to compliment my first one in a stereo setup with the Z9 I got. It was an old store display model, VLF, and still in good nick.

    However, I’ve watched two movies which had this happen, the one last night as most are probably familiar with it, U-571 (GREAT BASS), and the scene where the German plane flies at them and they are debating to shoot at it or not.

    We got a great sound effect [​IMG], though not a technically great one I think. There was a kind of great 'crack' noise at the peak of the loudness when the plane flies over, like a gunshot from the left front of the room. My volume was at -14.5dB

    I first thought it was my left front speakers, but I played it through a couple of times slowly increasing the level of volume, and nothing happened, sounded as it should. I then tried one last time with the volume at -11dB and took the grill off the sub for interest and played the scene again, just to see if it was the last thing I would expect, the sub.

    I swear I nearly fell over, I got a heart attack and nearly crapped my pants when it happened, especially sitting less than half a meter away from the sub. The diaphragm (I think it’s called) move a huge amount and the gunshot happened again. I've never heard anything like it, it sounded good from the back of the room, but boy, did it sound great sitting next to it, though i don't know if my ears would survive doing it to many times. [​IMG]


    why is this happening, I’m assuming it's not good for the Sub-woofer, and I’m asking it to do something out of it's specs maybe, but why is it happening, and what is actually causing the cool gunshot noise?

    Thanks [​IMG]
     
  2. EricRWem

    EricRWem Screenwriter

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    Two subs?! You're a crazy man! [​IMG]
     
  3. Dustin B

    Dustin B Producer

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    Sounds like you're bottoming the sub which is really bad for the driver. Keep the level below where this happens.

    If you haven't yet, you really should get an SPL meter and a calibration disc.
     
  4. Brad_See

    Brad_See Stunt Coordinator

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    I always get a little nervous listening to Darla tap on the fish tank in Finding Nemo. It sounds so awesome but when I reach up under there I can feel some massive excursion from the driver and I can feel the sound pressure on my ear drums. It doesn't seem distorted though (Dayton 10") but it's obviously not tuned to whatever frequency the tank tap is producing!

    brad cook
     
  5. Edward J M

    Edward J M Cinematographer

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    Ditto what Dustin said.

    The voice coil former is smacking the magnet backplate. Eventually you will deform the VC former, misalign the coil, and it will start scraping in the gap, eventually causing total failure. Other types of failures are ripped/torn spiders and surrounds, and broken tinsel leads from over-excursion in the outward direction.

    Bottom line - TURN IT DOWN (for now), calibrate the system, and know its clean limits. If you want it louder, then buy bigger/better/more subwoofer.
     
  6. Kaj

    Kaj Stunt Coordinator

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    i've turned it down, and i'll redo my setup again (i do have a sound meter). but i'll admit i do like a bit of of the WOW effect, so it was a bit higher than i should have been.

    thanks for the info, i at least know now why it's happening [​IMG]

    cool sound effect though


    cheers

    oh yeah, you think two woofers it bad, the new Denon flagship seems it'll do THREE! [​IMG]

    that's a bit of an over kill even for me!
     
  7. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    If you don't have one now, you might consider putting a subsonic filter on your sub, set to your sub's lowest extension point or to the frequency the ports are tuned to. That will help prevent bottoming, reduce port loading/chuffing, and let you turn it up louder without endangering the voice coil.
     
  8. Kaj

    Kaj Stunt Coordinator

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    i don't think the sub is designed for what i may be asking of it anyway, i'll just probably look into a new, bigger sub, that's all.

    thanks for the info
     
  9. alan halvorson

    alan halvorson Cinematographer

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    I am not familiar with Velodyne's current subwoofer offerings, but doesn't Velodyne include a limiter circuit in their powered subwoofers that prevents overload and bottoming? I know they used to.
     
  10. Greg-ST

    Greg-ST Stunt Coordinator

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    Shouldn't worry about it unless the sub is bottoming out (you should know when it does as it'll likely make a clacking sound). I don't think I've ever bottomed my Dayton out, even when I've had the volume up to extremely high levels. You can get some crazy excursion out of it. I've watched it during bass heavy stuff at high volumes. The driver can really move.

    Enjoy it [​IMG] Mine wows me all the time. The performance I can get out of this thing is truly phenomenal (especially for the price).
     
  11. Kaj

    Kaj Stunt Coordinator

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    that may be true and i'd be interested to know as well, but the one i have with this 'problem' is, as i said, an older one and is discontinued by Velodyne, so it may well be that they now have some sort of protection built in.
     
  12. George_W_K

    George_W_K Screenwriter

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    You are the first person that I've ever heard actually like the "clack" of a bottoming sub.[​IMG]

    If you upgrade or get a subsonic filter, keep us updated.
     

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