Sub making terrible sound NOT bottoming OUT?

Discussion in 'Archived Threads 2001-2004' started by Robert Sun, Mar 3, 2003.

  1. Robert Sun

    Robert Sun Agent

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    Hello,

    At first I thought my sub was bottoming out during LOTR: FOTR (Sauron's finger cut off and explosion scene) but after reading through some threads I don't think the terrible noise is caused by this.

    I read that bottoming out sounds like "farting" or "pop sound". I created a bass test tone CD and tested my subwoofer with it. I can manage to get a reading on RS SPL meter @18.8 Hz of 56 dB. Can't register anything below that. When I pump up the volume at 18.8Hz I can hear the farting/pop noises (I would describe it as clicking??). I assume this is bottoming out since my sub is rated to 25 Hz. When I reach 25Hz the noise stops even at high volume.

    During LOTR scene it makes a noise I would describe as "vibrating" but not popping or clicking. I read someone else saying it may be clipping? Does anyone know from my basic description what my sub is doing?

    Any help/thoughts appreciated
     
  2. Willem Vos

    Willem Vos Stunt Coordinator

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    It could be your sub is vibrating so badly, that it is "dancing", or otherwise "activating" something else in your viewing room, maybe close to the sub. Is it on spikes?

    Putting a small carpet under the sub, or something similar usually solves this.

    What I've also experienced with my first sub, was that the "surround" material of the speaker cone made a flabby vibrating sound at low frequencies (at which point the cone was really moving violantly).

    Are you sure the sound is coming from your sub? If the amp IS clipping, the only solution would be to lower the volume on the sub.

    You could try running a subwoofer test-tone, and check if the sub is still making the noise. (don't keep the test-tone on for too long, or the sub-amp will get pretty hot)

    What kind of sub is it? sealed or reflex?
     
  3. Mitch Stevens

    Mitch Stevens Supporting Actor

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    My guess is that it's vibrating something else in the room, and you can't find it. When I turn up my old sub very loud, the walls start to vibrate very loud, and the door frames, are the ones that make the most noise. I actually have to hold the door frames down with my hands just to get it to stop vibrating so badly.

    Put the LOTR scene in a loop, and walk around the room playing very close attention to what might be causing the vibration. Sometimes, you won't find the source, unless you're really looking for it. It took me a while to realize it was my door frames that vibrated.
     
  4. Geoff L

    Geoff L Screenwriter

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    It is difficult to make a solid diagnious from your post.

    What is the sub brand model if you don't mind telling.
    The clicking at loud spl at 18hz is probley the driver bottoming and or being distored from the amp clipping or the driver unloading below tuning if ported

    If it's ported is could be the driver unloading under the tuning point as mentioned.

    Could be vibrations in the room as others have mentioned.

    The sub amp could be clipping and cause the driver to produce distorted lower bass freq response if the amp contains no sub sonic filter below tuning.

    Some thing could be loose "on or in" the sub. Check all the screws holding the driver and amp to the cabinet.

    The driver could be starting to fry it's voice coil.
    Pushing the driver slowly in with your thumbs (centered on each side of the dust cap) and listen/feel for scraping or a scratching sound. DON'T PUSH ON THE DUST CAP, but just to the side of it on both sides.
    Do this with the sub off or not playing and be carfull to be centered evenly on both sides when pushing in and letting it come backout with your thumbs still in place lightly. You want to be pushing slowly and evenly on the cone with even force on both side of the cone.
    Any scratching or scraping is not a good, and a sign that the driver is on it way out.

    All are just guessing and things you may want to check out.

    Regards
    Geoff
     
  5. Robert Sun

    Robert Sun Agent

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    Hi All,

    Thanks for the ideas.
    Geoff my sub is Sound Dynamics RTS-1000 (made by same people who make Energy, Mirage). It is a ported reflex sub. The sub is only new and it has always done this in LOTR since I had it.

    Mitch, I found an old heater rattling but it is not making the noise I was concerned about.

    Willem, I think you describe the sound pretty well. Flabby vibrating sound is more like what I think mine is. How did you fix the problem?
     
  6. Justin Ward

    Justin Ward Supporting Actor

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    I doubt it is clipping. Why would the max volume be differant for varying frequencies? For example, isn't it just as easy for an amp to send 100 watts in 15hz as it is for the amp to push 100 watts into 50hz?
     
  7. Willem Vos

    Willem Vos Stunt Coordinator

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  8. Jim_P

    Jim_P Stunt Coordinator

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    Hi Robert:

    First of all, you should be aware that the Lord of the Rings DVD has some weird low frequency stuff going on. There have been other threads about this being the DVD that damages speakers.

    Ported subwoofers are designed to be able to be played louder, yet they do tend to distort at the lower frequencies.

    Have you heard the same noise from other DVDs, or just the LOTR FOTR?
     
  9. Robert Sun

    Robert Sun Agent

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    Jim,

    Just seems to be in that particular scene is the only time I have noticed it. Someone said the bass at the end of Chapter 13 in MOnsters Inc is quite low and I have no probs with that one....
     
  10. Willem Vos

    Willem Vos Stunt Coordinator

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  11. Craig Morris

    Craig Morris Stunt Coordinator

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    I find these threads very intriguing... I'm always amazed at people who can over-drive their subs.

    Both my brother and a friend of mine use the 8" version of the same Energy/Mirage/Sound Dynamics sub described in this thread.

    I have auditioned both extensively and have never heard them misbehave. In fact, my friend listens to music FAR louder than I can stand, and he's a bass fiend, and has a much larger room than mine, and yet his 8" Energy NEVER misbehaves. If anything, I'm amazed at the loud, clean bass that comes out. If I'm not mistaken, these subs have a protection circuit that is meant to keep them from being overdriven. Evidently it works very well.

    In contrast, another friend has the new PSB Subzero-i sub... which is an 8"/100w sub similar to the API product. His sub has a nasty rattle inside it that is easily excited, even at what I would call very reasonable volume levels (particularly compared to what I've seen from the API subs). Either PSB's protection circuit is inferior, or his sub is defective.

    If I were you Robert, I'd be tempted to ask your dealer to try another sub (maybe he has a demo you could borrow?)... as I said, I've never heard the 8" misbehave as you've described, so I suspect the 10" shouldn't either. Does it only misbehave at very loud volumes? or would you say the LoTR scene causes this behaviour even at moderate volumes? If it does it at moderate volumes, I'd suspect that something is wrong with the sub.
     
  12. Geoff L

    Geoff L Screenwriter

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    Robert

    More than likely the bass in the LOTR scene is very deep (teens with decay dropping well below that) and most likely well below your subs tuning point. The 10" driver is "unloading" and that more than likely is what your hearing.

    If the sub seems fine on most all material, then the amp probley dose not have a "sub sonic fliter" built into it just below tuning to "protect" the driver from this. This would explain the possible nosies your hearing. ~{I would think that it would have one built in, and if so it may not be functioning properly}~.

    =======>
    The driver is just flapping around uncontroled and sounds nasty when this happens, even at lower voumes right?
    =======>

    If you were to turn in up while this is happening (would'nt take much either) the driver would more than likely bottom out prematurly or the amp will clip or both.

    =======>
    You may have some port/slot chuffing going on along with this. I don't know what type porting it uses...
    =======>

    I am not familar with that exact sub but do know who SD is.
    Dose the subs manual say anything about a SS filter built in for driver protection?
    Might also be be called a corner filter, this is their to protect the driver and amp from trying to produce signals well below the subs tuning point.

    Some of the first SVS subs had no SS filter and you heard of people bottoming out their sub/subs, or it making god awful noises.

    Regards
    Geoff
    I tend to agree with the poster above as it apears "it should have" SS protection from what he wrote and your maynot be working.....
     
  13. Willem Vos

    Willem Vos Stunt Coordinator

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  14. Lee Bailey

    Lee Bailey Second Unit

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    Try plugging the sub's port with a roll of socks and see if this helps. If so, it sounds like the driver is unloading, and you will either have to get a better sub, or just turn it down. I'm assuming that you have calibrated your system using a SPL meter? How hot over the mains are you running it?
     
  15. Craig Morris

    Craig Morris Stunt Coordinator

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  16. jason willder

    jason willder Stunt Coordinator

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    Just two weeks ago my Servo-15 did what sounds like the same thing. It turned out to be a loose connection on the amp. Maybe something has vibrated loose on the inside. Good luck.
     
  17. Robert Sun

    Robert Sun Agent

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    Thanks for all the input guys appreciate it.
     

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