Slot Port Calculator?

Discussion in 'Home Theater Projects' started by Kincade, May 26, 2004.

  1. Kincade

    Kincade Second Unit

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    Hi all. I'm currently building a 5 cubic foot box with a Blueprint 1503 tuned to 20 hz... It calls for a 6 inch port of 33" long..

    Considering I'd have to use elbows, and it would still have some port noise, i'm debating on a slot port. However, i'm unsure how to calculate the port dimensions. Unibox doesn't have a provision for a slot port, only round.

    How would I calculate the port dimensions of a slot port compared to a round?

    Thanks in advance,
     
  2. Geoff L

    Geoff L Screenwriter

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    To figure your port, square/slot/round and different tunings for your box, try here. Select Loudspeakers-101 and then check fro that menu (design port/s) and click on that. Some very basic info is given, and a calculator is their for giving you the deminsions you'ed need for a particular tuning using round, square or slot port/s.

    Just punch in your box volume etc, along with width & height of the slot & the calucuator will do the rest. ~{Including telling you if you've done something wrong, or do not have enough port area}~...

    I use it for all kinds of quicky driver box and port sims, and it seems to work quite well.

    Works in ft^³ and inches, NOT, LT's and cm's........

    Others may provide info that will suite your question better, but this should get you started.

    Regards
    Geoff
     
  3. Kyle Richardson

    Kyle Richardson Screenwriter

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    I know WINISD PRO has the ability to change to a square or rectangular port but I'm not sure how accurate it is or if it also accounts for the end correction value. You can calculate it by hand using formulas and instructions on this page.
     
  4. Kyle Richardson

    Kyle Richardson Screenwriter

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    Here is the link that Geoff was talking about. I forgot about that one and it also includes a radio button to select if its a slot port which probably accounts for end correction values. It says to use a ratio of less than 1:8 (height x width) but I'm pretty sure you can go 1:9 and still be okay.
     
  5. Geoff L

    Geoff L Screenwriter

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    Thanks Kyle

    Yes, 1:8 is text book, but found 1:9 works fine and it's supposed to account for end correction...

    You can put your pen down now...[​IMG]

    Cheers
    Geoff
     
  6. Kincade

    Kincade Second Unit

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    Thanks to both of you! I'll try that calculator. Strange though - if I uncheck "is this a slot port", it adds quite a bit of length.. Reading on the JL audio webpage, it looks like a slot port should be a little LONGER than a square port, due to the end correction factor. Any thoughts?

    I should mention, for anyone that hasn't dealt with Kyle so far, I HIGHLY recommend him. He's spent a whole lotta time with me so far helping me with this, and even went so far as to let me come up to his house and listen to his sub/system.

    And man oh man - for anyone who hasn't seen the 1503 in person - i'm hard pressed to describe it! I really hate to put it in a box and hide it! ;-)
     
  7. Kincade

    Kincade Second Unit

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    A final question - if I use a slot port, would a configuration like this work:

    --------------
    | |
    | |
    | |
    | |
    | |
    | |
    | |
    |---------- |
    | ----------|
    |---------- |
    |
    --------------

    Or does this introduce too many bends to the equation?

    Would the length of the ports here be wall to wall? (ex., if the box is 10" deep, then would the total port length be 40"?, not figuring the end correction factor that JL audio lists)

    TIA,
     
  8. Brian-K-Owens

    Brian-K-Owens Stunt Coordinator

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    I have always thought the slot port info on the JL-Audio site was crazy. The formula seems to be too general. The calculator on loudspeakers101 works great every time for me.

    The slot port benefits from the additional resistance of the extended sidewall. Since the port is a type of resistance, it only make sense that adding resistance would be equivalent to a longer port.

    Brian
     

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