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port dimensions

Discussion in 'Home Cinema Building DIY' started by go5, May 20, 2003.

  1. go5

    go5
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    I am building my first sub, and after all my research and finally getting a volume, etc. I am having trouble with the port. Does anyone know a sure way to figure out what the dimensions of the port should be? I have tried a calculation in a book, and a few programs and spreadsheets. Everyone comes up with a different answer.

    Any help is apreciated. Thanks
     
  2. micb3rd

    micb3rd
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    Port dimentions are determined by what speaker you are using (Thiele and small paramaters) enclosure size, vent mouth area and vent tuning point.

    It is normally useful to use WINISD or simular software to model your driver and enclosure to have a good play to find a good responce.

    What subwoofer driver are you using?

    I may be able to surgest a few designs for you.
     
  3. go5

    go5
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    I have posted my other t/s parameters on other postings and got all the information I needed as far as box size, etc, etc, but I am just stuck on the port. Like I said just keep getting different port sizes depending on prog, book, etc.

    These are my paramters

    Driver coustic ht-812
    Vas 130.000 litres
    Qts 0.320
    Qes 0.450
    fs 26.0 Hz
    Xmax 7.62 mm
    Dia. 30.48 cm
    PEMax 250 watts

    Constants
    Ro 1.18 kg/m^3
    c 345.00 m/s



    Enclosure Specifications
    Desired Qtc 0.60
    Qr 1.88
    Vr 2.52
    Vb 51.68 litres
    Fb 34.66 Hz
    F3 39.1 Hz

    Sd 7.30E-02 m^2
    Vd 5.56E-04 m^3
    n0 0.005
    SPL 88.9 dB/1W/1m
    K1 0.741
    K2 110.696
    Amax 1.000
    Par 0.741
    Per 151 watts
    PeakSPL 113 dB
     
  4. go5

    go5
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    okay so this is why i am so confused...

    for port sizes these are the calcs i get

    winisd - 3" wide 5 " long
    4 " wide 10 " long

    formula from book - 3" wide 10" wide

    website spreadsheet - 6" wide 5" long

    see why I am so confused, any suggestions anyone?

    thanks
     
  5. micb3rd

    micb3rd
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    I modeled subwoofer driver, the default WinISD box looked ok, it comes up with a enclosure of 60.5 Liters, a vent tune 32.95 hz which gives a port 4.02 inch diamater by 11.51 inchs depth.

    The subwoofer will not drop to the deepest of low bass but it looks like it will have ok performance above 30 hz.

    Its is a 4 ohm driver so what are you going to use for amplification?
     

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