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Spice Model for Loudspeaker

Discussion in 'CAD' started by Jim Thompson, Sep 23, 2004.

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  1. Jim Thompson

    Jim Thompson Guest

    I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
    DISPLACEMENT as the output.

    Thanks!

    ...Jim Thompson
     
  2. I read in sci.electronics.design that Jim Thompson
    I suppose there is no point in asking why. Go to:

    www.klippel.de

    My esteemed colleague Wolfgang Klippel will either already have a
    solution for you or will, I feel sure, help you towards one. What he
    doesn't know about loudspeakers isn't known by anyone.
     
  3. Jim Thompson

    Jim Thompson Guest

    Moving a mirror ;-)
    Thanks!

    ...Jim Thompson
     
  4. Joerg

    Joerg Guest

    Hi Jim,
    And here I thought you wanted to install a huge boom box in your car,
    tint the glass, put on mag wheels....

    This lab might be able to help, at least when it comes to the calculations:

    http://www.linkwitzlab.com/x-models.htm

    Regards, Joerg
     
  5. Jim Thompson

    Jim Thompson Guest

    I actually designed boom boxes in my youth (mid-40s :), bought several
    ZXs, and did the whole middle-age-crazy bit, grew a beard (which I
    still have, but it's salt-and-pepper now).
    Thanks for the link!

    ...Jim Thompson
     
  6. E. Rosten

    E. Rosten Guest

    Interesting. What for? If you need precision, you'd be better off
    designing a control loop to set the precision exactly. Of course, a
    spice model would help the design... :)

    -Ed


    --
    (You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

    /d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
    {moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
    for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage
     
  7. Jim Thompson

    Jim Thompson Guest

    There *will* be a control loop. Model is needed to evaluate best
    approach.

    ...Jim Thompson
     
  8. Rich Grise

    Rich Grise Guest

    I wonder how big this mirror is intended to be? The idea of an
    electrostatic speaker springs to my mind, or maybe capacitive
    feedback from the voice coil/mirror arrangement - it will need
    some kind of feedback, right?

    Thanks,
    Rich
     
  9. Joerg

    Joerg Guest

    Hi Jim,

    Just one other idea: There used to be "cone-less" speakers. Basically
    these were just the coils with a counter mass. This was screwed to
    whatever surface needed to be insonicated. I don't know whether these
    are still marketed but I remember they worked ok and were designed for
    use with full size stereos. I think some vendors called them invisible
    speakers.

    That solution would at least take part of the components out of the
    equation.

    Regards, Joerg
     
  10. I read in sci.electronics.design that Joerg <[email protected]
    They have more or less been reinvented, with a bit more science applied,
    and embodied in 'flat-panel loudspeakers'.
     
  11. E. Rosten

    E. Rosten Guest

    There *will* be a control loop. Model is needed to evaluate best

    Jim,

    Could you let me know how you get on with this, if that's OK. I've just
    come across something where a bass loudspeaker may be the best kind (ie
    cheap, avaliable, right kind of frequencies avaliable) of actuator.

    One problem is that I can't figure out the best way to atach the actuee
    (if that is a real word) to the speaker. Gluing something to the center
    of the cone may work, but one has to be careful since you mustn't cause
    the whole thing to move off axis (lots of friction if that happens).
    Also, loudspeakers are designed for moving air, which suggests that the
    whole assembly is less efficient that it could be since it's moving
    large amounts of air around. I can not, however think of a good way
    around this since the cone also performs the job of keeping the coil in
    the correct place, rather well.

    One could alternatively place both sides in an air tight box to improve
    the springiness that returns the speaker to the original position.

    Anyway, one could presumable measure the displacement of the cone by
    looking at the inductance of the coil, since the further in it is, the
    more inductance it will have. However, I can't think of a good, high
    precision way of measuring the displacement required to calibrate that.

    Any thoughts so far?


    -Ed

    --
    (You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

    /d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
    {moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
    for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage
     
  12. You can glue a tube to the rim of the voice-coil former (under the dust
    cap). You keep it centred by putting a support across the open end of
    the bucket, having a carefully-placed hole through which the tube
    passes.
    You can (carefully!) cut holes in it. But if you want more than a few of
    these, a loudspeaker manufacturer (no, not one in China!) will make you
    cone-less units with a heavy-duty rear suspension or a double
    suspension. For $$, of course.

    If you are using the driver unbaffled, the effect of the cone is minimal
    at frequencies below that at which the circumference of the driver rim
    is less than half a wavelength.
    You could. The boxes might have to be quite big, and they can't be quite
    air-tight because they will 'blow' the cone as the air pressure changes.
    The inductance changes in a complex way with position. The magnet
    structure is close to saturation, and there is sometimes a conducting
    element in the pole-pieces to create electrical damping.
    I posted a link to Wolfgang Klippel's site. One of the topics he has
    researched in depth is the measurement of cone displacement - to high
    precision. It's *difficult* - he uses a laser.
     
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