Closed Thread
Results 1 to 9 of 9

Reload Thread: I need the math behind port WxH, hz, and length. Help!

  1. #1
    MrBananaMan's Avatar
    MrBananaMan is offline Junior Member



    Join Date
    Jun 2009
    Location
    Michigan
    Posts
    7
    Post Thanks / Like
    Mentioned
    0 Post(s)

    I need the math behind port WxH, hz, and length. Help!

    Hey guys, I am going to be extending a port on my box that is tuned to 41.5hz, to 31.5 hz. The length is currently 18 inches and I need to get it to ~35.85 inches. For this, I am going to have to bend my port multiple times to fit in my trunk. This means I need to know about how bending affects a port, AND the math behind the relationship between port width, height, length, and hertz. I can't rely on a solid length and then change the port opening size to get a certain hz, becuase I need a different length!

    So, if anyone has any information on this, especially the math formula, I was would pleased to hear from you.







  2. #2
    spl_robb's Avatar
    spl_robb is offline Member



    Join Date
    Jun 2009
    Location
    SD
    Posts
    108
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    just remember also that by extending your port you will lose cuft on the box and that also afects the tuning(hz)




  3. #3
    MrBananaMan's Avatar
    MrBananaMan is offline Junior Member

    Threadstarter


    Join Date
    Jun 2009
    Location
    Michigan
    Posts
    7
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Hmm ok will that make a
    Noticeable difference? Also, any idea on how I can manipulate the port without a huge
    Equation? Since I know my 3 dimensions already, can I take their volume, keeping their hxw consistant, and bend it as much as I want?




  4. #4
    MrBananaMan's Avatar
    MrBananaMan is offline Junior Member

    Threadstarter


    Join Date
    Jun 2009
    Location
    Michigan
    Posts
    7
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Oh sorry I read cu ft wrong in your post. The rest of the port will be
    On the outside of the box so I won't lose any cubed ft




  5. #5
    Pioneer~Saturn's Avatar
    Pioneer~Saturn is offline Dr. Enclosure



    Join Date
    Jul 2006
    Location
    Dayton, OH
    Age
    26
    Posts
    5,318
    Post Thanks / Like
    Images
    7
    Mentioned
    1 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Ok, here's the what you need to do:

    -Find the port area

    -Find the port length from the center of the port through the whole thing..bends, etc (it's much easier to make your enclosure on sketchup instead of doing this on paper/thinking it out)

    -Find the net airspace left inside the enclosure after you take away the port's displacement and the sub(s) displacement...find it in cubic INCHES

    After you've found these three pieces of info you can find your tuning with this:

    -Square root of the port area

    -Mulitply that by .823

    -Add your port length onto that

    -Multiply this by the net airspace you found in cubic INCHES

    -X-Save the number you have now for future use-X-

    -Now take 184000000 multiplied by the port area

    -Then devide by the number you came up with in the previous steps

    -Square root this number

    -Multiply by .159

    You now have your tuning (if your specs were calculated correctly)


    Knock yourself out And remember:
    -Longer port length = lower tuning
    -Smaller port area = lower tuning
    -Larger airspace = lower tuning

    Hope that helps



    <First and only dual-alternator 'real' Saturn (pre 2002) on the planet>
    Team Concepts, Team Shok Industries Team XS Power
    Soon: Mystery subs + AQ20k
    12.75 cubes net ~25Hz tuning 200 sq inches of port (lowz?)
    AC position- 250 amp alt
    Stock alt position- 225 amp alt
    (2) XS Power D3100's
    4 power+ 4 ground runs of 1/0-gauge to rear
    152.1 @ 40Hz legal, certified...just getting started.

  6. #6
    KOL's Avatar
    KOL
    KOL is offline Senior VIP Member



    Join Date
    Jan 2009
    Location
    my house
    Posts
    218
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    The more bends in the port the more turbulence/port noise you'll create. Just build yourself a whole new box.




  7. #7
    MrBananaMan's Avatar
    MrBananaMan is offline Junior Member

    Threadstarter


    Join Date
    Jun 2009
    Location
    Michigan
    Posts
    7
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Thanks for the help saturn! This will come in handy.

    To KOL: I'm strapped on cash so I'm trying to make due with what I have atm (college = little money). I'm starting to think pvc tubes are a better choice now because I can just seal my current slot port with wood and bend some tubes up for the inside, while also easily being able to extend the port outside of the box too, if necessary.

    If I did do this, would a 6" diameter be enough for each chamber? Or should I double up. I'm running 2.25 ft^3 airspace for each sub right now, which will be 2.5^3 after chopping down the old port. What do I factor in a second port if necessary?




  8. #8
    406er's Avatar
    406er is offline box builder extraordinair



    Join Date
    Sep 2005
    Location
    Winnipeg,Mb
    Age
    32
    Posts
    1,043
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Quote Originally Posted by KOL View Post
    The more bends in the port the more turbulence/port noise you'll create. Just build yourself a whole new box.
    X2

    if you cant do it right, dont do it at all



    Head installer for Hamilton Audio
    Macrom, Stetsom, RD and Sundown car audio

    1999 Jeep Cherokee Sport
    Eclipse CD3100 head unit
    Steg Audio System F4 380 4ch amp
    Macrom M2 6 1/2 comp set
    RE RE 10

    dB set up
    SD3000, SPL12 143.4dB (in my 91 Sonoma)
    http://www.sounddomain.com/ride/759285

  9. #9
    MrBananaMan's Avatar
    MrBananaMan is offline Junior Member

    Threadstarter


    Join Date
    Jun 2009
    Location
    Michigan
    Posts
    7
    Post Thanks / Like
    Mentioned
    0 Post(s)

    Re: I need the math behind port WxH, hz, and length. Help!

    Quote Originally Posted by 406er View Post
    X2

    if you cant do it right, dont do it at all
    No thanks!




Closed Thread

Posting Permissions

  • You may not post new threads
  • You may post replies
  • You may post attachments
  • You may edit your posts

1e2 Forum