Newbee needs help on driver firing position

Discussion in 'Home Theater Projects' started by Don McKinnon, Jun 6, 2003.

  1. Don McKinnon

    Don McKinnon Auditioning

    Nov 28, 2002
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    I'm building my first sub project. Going with a Shiva driver and AVA250 amp in an 88 L sealed enclosure. My interest is mostly music. I would prefer the driver be in the down firing position for aesthetic reasons. Are there any advantages or disadvantages to the driver firing down as compared to in a forward position? I have seen some reference to a claim that the driver might wear out over time quicker if always facing down - others have suggestted that this is not case.

    Thanks in advance.

    Don [​IMG]
  2. Jonathan T

    Jonathan T Second Unit

    Nov 6, 2002
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    You can mount that driver facing down. There's really no problem with it. Over time as the surround wears out, it will sag somewhat but shouldn't happen for decades as long as you take care of your investment.
  3. Bob Kavanaugh

    Bob Kavanaugh Second Unit

    Jan 17, 2003
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    Loss of Xmax due to driver sagging is the only downside I can think of.

    According to Adire:

    Many low-Fs drivers cannot be mounted in a downfiring (or horizontal) configuration; they must be
    oriented vertically, with the cone/basket perpendicular to the floor. To achieve a very low Fs in other
    subwoofer systems, the moving mass of the system is made quite high, while the stiffness of the suspension
    is made low. These two changes work to create a system which will suffer excessive cone offset when
    mounted so that gravity will pull the cone out, away from the normal “rest” position.
    Because Shiva has an Fs of 21.6 Hz, the moving mass is not substantially more than competitive
    subwoofers. However, the surround is considerably stiffer. This results in Shiva being rated for horizontal
    mounting. In fact, given the T/S parameters, one can calculate the effective loss in Xmax that will occur
    due to the offset of the cone from the force of gravity:
    Basically, one looks at the mass of the cone (118.3 grams, in the case of Shiva), and the mechanical
    deflection, Cms (0.47 mm/N, as measured by DUMAX). The acceleration of gravity (what's pulling the
    cone down, or up) is 9.8 m/s2.
    Now, a Newton (the N in Cms’ units) is in units of kg * m / s2, or kilogram meter/second squared. So,
    multiply the mass of the cone by the force applied (gravity) by the mechanical deflection:
    mass * force * deflection = 0.1183 kg * 9.8 m/s2 * 0.47 mm/N
    = 1.1593 kg * m / s2 * 0.47 mm / (kg * m / s2)
    Note that there's a kg * m / s2 term in the numerator and the denominator. Cancel the units out, and you're
    left with 0.545 mm. Thus when Shiva is mounted horizontally, one will end up with an Xmax of
    14.355mm one way (in the direction of gravity), and 15.44mm in the opposite way. As a comparison,
    several other high-end 12” subwoofer drivers will exhibit up to 1mm of offset; considering these units
    typically start with 2+mm less Xmax than Shiva, the result is a considerable drop in swept volume.

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