Why do speakers need a neutral/rest position?

Discussion in 'Speakers' started by Matthew Will, Mar 11, 2004.

  1. Matthew Will

    Matthew Will Stunt Coordinator

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    Here is my thinking about the spider/suspension. Besides the fact that the spider/surround keep the coil lined up in the middle of the gap does it have a place in the speaker? Once energy starts moving through the coil and it starts moving is there anything useful, besides lining up the voice coil, that the spider is doing? If the polarities are constantly switching in the coil then would it not control its own up and down movement and not need this resisting force to bring it back to the middle?

    Imagine a speaker that doesn't have a spider or surround to restrict the linear motion but has some sort of suspension that does keep the voice coil lined up correctly in the gap. Also assume that this system does not allow for the voice coil to ever leave the gap in a way that it can't bring itself back in. Does the speaker need the voice coil to be brought back into the middle of the gap linearly?

    Picture the magnet on a speaker. The speaker is firing up. The top of the magnet is north and the bottom south. Now imagine sending a signal through the coil and it has no suspension to restrict is linear motion. It is sent a signal that gives the coil a north polarity. The coil moves down, but not out of the gap entirely. It never leaves the Xmag. The signal stops and the coil drops to the bottom due to gravity. Say another charge makes it north again and keeps it pushed down. Even if the signal is only for half a second and at only 20 Hz then the speaker still changes polarity 10 times meaning that the coil will be down for one time then gets shot back up to function just as a speaker with a traditional suspension works. I don't know if anyone would be able to notice that 1/20th of a second. Then as the Hz rizes then that smal delay gets even smaller.

    Then also if the speaker is at full down position with a previous north charge and the amplifier sends the opposite south charge to it then it doesn't miss a beat and is swung into the up position immiediately.

    One problem I can think of for a speaker with a suspension that doesn't restrict linear motion is that perhaps it would be like a chain reaction where if it is not brought back to the middle then the speaker coil would have to be ultimately shot off. For example a large signal sends the coil into the upper north section of the magnetic gap. Before the speaker can drop the frequencies and amplitudes change so that it needs to vibrate quickly. So does it get stuck in that upper quadrant and the next big signal sends it smashing past Xmag or will the voice coil find its own equilibrium within the magnetic gap?

    This is all extremely confusing and I need to start reading up on magnets. Does anyone else here know anything about what I'm talking about? I know that no one knows exactly what I'm talking about because this is just a rediculous hypothetical topic. I want it answered though. blahhh...I might need some sleep after thinking about this one.
     
  2. Yousaf

    Yousaf Second Unit

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    The most obvious problem that comes to mind in such a situation is that the acceleration due to gravity is only 9.8 m/sec^2. I vaguely recall doing some physics calculations once and the acceleration of the cone was MUCH, MUCH greater. Such a speaker would probably only be able to play the lowest of the low notes.
     
  3. John Garcia

    John Garcia Executive Producer

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    It's an interesting theory, but at 20Hz, what would you dissipate heat with in a larger driver capable of being flat at this frequency? Just the motor structure? How will you attach the motor structure to the driver (meaning you do need to come up with some kind of suspension)? What keeps the driver rigid? Sounds like what you are saying is you would have the motor structure mounted on one wall, and the cone on another, with no basket connecting them, is that correct?
     
  4. Matthew Will

    Matthew Will Stunt Coordinator

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    Why would that be? As long as the magnets do find their own place then it would react just like a regular speaker. Right?

    So for now what I really need answered is, if a speaker does not have a resistive force to bring it back to a neutral position, how do the magnets react? If the speaker is able to fall to complete xmax, would it be able to bring itself back to a regular position and transition even if only a small signal was sent through? Anyone know for certain? Matt
     
  5. Jesse Sharrow

    Jesse Sharrow Supporting Actor

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    Isnt it to stop the driver from bottoming out or just tearing itselfe from the surround and flying out of the basket.
     
  6. Matthew Will

    Matthew Will Stunt Coordinator

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    Well I think its more to keep the voice coil in the middle of the gap perpendicular to the motion of the speaker. I'm wondering if the coil would keep its own equilibrium within the coil in terms of linear motion with the cone. Matt
     
  7. John Garcia

    John Garcia Executive Producer

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    How would it keep that linear motion? There would be nothing to keep it in check?

    Yes, the basket is a factor in heat dissipation, but that may be more relevant to certain drivers than others, definitely with high performance sub drivers.
     
  8. Matthew Will

    Matthew Will Stunt Coordinator

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    Well this is a huge hypothetical question. If you want an answer to your question then all I can say is im sure there is a way to keep something moving linear but not move perpendicular to the linear motion. It's possible. Itd be a complete redesign of the suspension for sure. But yea..its a hypothetical question. Anyone have an answer to my question about the magnets? Matt
     

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