random one.....sub suspended from roof

Discussion in 'Subwoofers' started by k13 wjd, Feb 7, 2009.

  1. k13 wjd

    k13 wjd
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    I know this one might cause a few arguements......


    Does anyone here, and im asking the diy guys......suspend thier subs from the roof, either using steel cable, or bungee cord.

    It may seem strange, but the best sounding subwoofer i ever heard, was a 15 inch driver, inside a 20 inch tube, 4 feet long.....and it was hung from the roof using 4 bungee cords...the type you all use in your boots to hold stuff down.


    Now, its obviously not the most attractive setup, but does anyone have thoughts on how it might perform acousticly.....i know its not going to work to well for the men here with monoliths.......but i'd like to hear peoples thoughts....positive or negative !
     
  2. GMC79

    GMC79
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    First Im kinda freaked out, was just thinking about that the other day!!! :eek:
    Seriously!!

    Sounds like a decent idea if space is a problem. No reason why it shouldn't work well. May have to think about that if i get a new bigger sub. :)
     
  3. k13 wjd

    k13 wjd
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    it is a "oldie" think......many many moons ago, loads of people used to hang their subs from the roof....


    I suppose loosing all floor vibration losses is a good thing....

    i think i need to find someone who actually knows lots about it.....its more of a DIY thing - the tube i saw/had was a serious peice of kit.....driven from a 21W RMS amp......and it was far louder than my 150W RMS tannoy subwoofer i currently have......says something for the man that built it........
     
  4. GMC79

    GMC79
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    21 RMS ? was that a typo? was it 210?

    Sounds good but would have thought a "dangling" sub wouldnt be ideal as speakers/subs need to be solid mounted ie spikes or stands for best results as to get all the energy into the driver?. Mayb wrong and may work well. Think i'd prefere some kind of solid ceiling mount.
     
  5. k13 wjd

    k13 wjd
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    no typo there....21W RMS.......

    perhaps my ears were more sensitive...it was a 15 inch driver, set in a chamber inside a chamber that was a tube.....the chamber was lined with concrete, and was around a foot deep....the driver faced the roof....wish i had photo's to show people.
     
  6. k13 wjd

    k13 wjd
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    all forces are equal and opposite....
     
  7. Nimby

    Nimby
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    Suspending a lightweight forward firing subwoofer from the ceiling would tend to soften the bass because there would be little or nothing to resist reaction forces from the driver. The subwoofer might actually start swinging!

    When hanging an upward or downward firing subwoofer both the cables/chains + enclosure mass would provide the resistance to cone movement reaction forces. The reaction forces are not simply the result of the lightweight cone itself moving back and forth but also the much greater mass of the air which is being pushed by the cone.

    I don't like the sound of car bungee chords unless the quality is unusually high. They tend to have quite a short lifetime in use particularly when under constant tension. Most aren't particularly attractive either.

    If I was going to suspend a subwoofer I would use stainless steel or galvanised steel stranded cables or chains and use all the handy kit available for attaching and tensioning them individually. A browse around any decent DIY store or builders merchant will provide enough kit to hang anything no matter what its weight or size.

    There was a fashion for hanging spherical speaker enclosures from a single cable back in the last century. Some supermarkets and department stores still have hanging speakers. They also have very high ceilings and lots of space! A large SVS hanging in a typical Victorian semi might become a little overpowering. :rolleyes:

    I can think of at least three other problems with suspended subwoofers:

    The clean styling of the steel cables might be spoilt by the need for signal feed cables and mains power. Chains might allow the cables to be woven neatly through the links.

    Rather than hanging the enclosure itself a strong suspended plywood platform might be a better choice to avoid spoiling the nice finish of the box or enclosure itself.

    You'd need to hang your cables from screw eyes fixed into the ceiling joists. You can't hang anything serious from plasterboard.

    As height is a factor in subwoofer performance and frequency response the results could be awful or great depending on your room and the subwoofer itself. Subwoofer suspension might become a fashion for fine tuning. Don't hold your breath though if SWMBO has any say.

    By sheer coincidence they are showing a chain suspended double bed on a French satellite programme at this very moment. <spooky> :)
     
  8. paulr2006

    paulr2006
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    Many years ago I was with a friend who was dismantling an old cinema, the speaker cabinet was huge & mounted above the screen. It was driven by a
    5W RMS Valve Amp....yes 5W RMS! the projectionist who had been there years told us that the previous Amp (before the upgrade) was 1W RMS! I guess the speaker was very efficient :D
     
  9. Nimby

    Nimby
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    The cinema speaker was probably horn loaded which can provide phenomenal output levels on low power amplifiers. There are still fans of horn loading and small valve amps if you search online.

    Horns have to be very large to be efficient at bass frequencies. So usually full range horns are split between bass horns, mid horns and treble horns to reduce coloration and distortion outside each horn's ideal bandwidth parameters.

    My first serious Hifi amplifier was a 10 watt mono Mullard 510 all valve pre-power amp. The neighbours once knocked on the wall when I played rock music too loud on my large folded horn. :suicide:
     
  10. k13 wjd

    k13 wjd
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    nimby.

    Thanks for your reply, and thoughts.

    I should have mentioned i have absoloutly NO intention of hanging my Tannoy 625 Alf from the roof.....i was just interested in the idea......


    the tube in question was ballasted with concrete.

    if the enclosure was on the ground, surely the sub "Pushes" down on the ground for every given stroke....all forces equal and opposite...right ?

    so if its susspended from the roof, surely there is less lost kinetic energy ? or am i a mile off ?

    could turn into an interesting topic....
     
  11. Nimby

    Nimby
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    A subwoofer driver in an enclosure is complex system. The linear cone movement is cyclical but subject to asymmetrical and often violent acceleration on dynamic peaks. The forced air movements and any ports also add their complexity to the model. Carried to extremes one might consider the True Infinite Baffle array where it requires considerable stiffening and/or very high baffle mass to limit reaction forces to a usable level. Any baffle (or driver) movement is lost information and reduced dynamic range with slower rise times on transients.

    With suspended subwoofers the cone must work against the mass of the enclosure to accelerate. In an extreme (imaginary) system of a giant driver and a balsa wood enclosure the cone would stay still and the enclosure would move instead. This is the same effect as fixing a series of 15" or 18" drivers in an ordinary lightweight stud wall. The cones stay almost still and the wall moves back and forth an inch or so! Been there.. done that. Didn't like it. Read the first chapter of my blog in my signature link to see what happened when I placed 4 x 15" IB drivers in a rather weak wall.

    One can imagine the gradually reducing effects of the driver reaction forces as the drivers becomes smaller and the enclosure or wall becomes heavier. Or in the extreme case one keeps on adding slabs of concrete until the cones start moving normally and the wall or enclosure stays completely still.

    You may be misunderstanding Newton's law in this context which states that every action has an equal and opposite reaction. The reaction forces generated by the driver are usually lost as heat energy in the enclosure mass. The reaction forces are still there but they are invisible.

    An interesting arrangement, much used in true IB subwoofers, is to nullify reaction forces by using an opposed driver manifold. Here the drivers move in opposite directions while fixed on opposite walls of a stiff box. The reaction forces are largely cancelled out. Suspending an opposed driver box from cables should ensure that it stays quite still while the cones can still move to closely match the amplified signal. The cones accelerate against each other's matching reaction forces.
     
  12. k13 wjd

    k13 wjd
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    im glad your here nimby......Your answers are first rate, and clear to understand.


    I had written about 30 lines in this space, about driver direction....but that can wait for another day....

    Thanks once again for your input nimby.
     

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