Pressure build-up in a vented sub???

Discussion in 'Archived Threads 2001-2004' started by PeterOS, Jan 25, 2003.

  1. PeterOS

    PeterOS Extra

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    Hoping some one might be able to help me out here. I want to find out what is the actual pressure build up inside a subwoofer, more specifically my Tempest Adire aligment. I want to do an analysis of how much the MDF moves under the pressure generated using ALGOR (its a Finite Element Analysis software).

    I was on this website and thought I was sorted but what the hell is Xv???
    http://www.silcom.com/~aludwig/Sysde...l_analysis.htm

    Here a section of it. (the equation that goes with it would paste for me)

    "A speaker cone with effective area SD moves sinusoidally with a peak excursion Xc. There is a vent of cross-sectional area Sv and length Lv. It is assumed that the air within the vent moves sinusoidally as a rigid mass with peak excursion Xv"

    Any help would be appreciated. I want to do up a graph of the differt Freq's against the pressure. Pump these values into ALGOR and see what it gives me. I presume the biggest pressure will be at thee box's resonant freq.

    If I get it done I will post the results for those who are interested. I will also be doing a analysis of the airflow through ported vents to see how much of a difference the vents make, these I will also post for those interested.

    Cheers in advance
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    My understanding is the air in the vent is treated as a "solid" slug of air with its corresponding mass and moves much like the cone of a driver.

    Pete
     
  3. PeterOS

    PeterOS Extra

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    Cheers for the reply Pete
    Just to be clearer, are you saying the the value for Xv is equal to the volume or the mass of the vent. The equations therefore being

    vol = (pie * radius^2 * length)
    or
    mass = (pie * radius^2 *length)*density

    Ex. For a vent of radius 3.75cm (diam 3") and length 28cm (11")
    The value of Xv would be 0.00149 kg (using mass eqn)

    Giving me a pressure for my 214L Tempest of

    76.244kg/m^3

    Anyone know if this sounds right???
    PLEASE REPLY
     
  4. Jonathan M

    Jonathan M Second Unit

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    I would say that Xv refers to the amount that that "solid" slug moves - not the volume of the air in the slug.
     
  5. Pete Mazz

    Pete Mazz Supporting Actor

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    This is his equation to derive pressure, substituting for X(v).

    [​IMG]


    X(v) is measured in meters.
    [​IMG]

    [​IMG]

    Pete
     
  6. Jeff Rosz

    Jeff Rosz Second Unit

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    i'll take a stab at clearing it up a bit. but im no mathmatics guru, so have a grain of salt.
    Xv would have to be a distance. therefore as johnathan stated, it cannot be a volume or a mass. as far as i can see, the equation pete posted is frequency dependent (which makes some sense to me). the variable that looks like a W represents angular frequency. "thats just my opinion, i could be wrong" [​IMG]
     
  7. Andrus_R

    Andrus_R Stunt Coordinator

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    My head hurts.([​IMG] _[​IMG] )
     

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