port length questions. how to measure

Discussion in 'Home Theater Projects' started by perry web, Feb 10, 2004.

  1. perry web

    perry web Stunt Coordinator

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    I am building a 118L vented box tuned to 20.5 fb. using pe's 250w amp and shiva mk IV driver.

    unibox says 17" port and winisd pro says 16.5". that is basically the same.

    I bought the 4" flared port kit. Is the length the overall dimension or the center section, not including flares?

    the assy is roughly 18" overall. the straight section is approx 16". so would I have to add or subtact and 1"?

    actually i am going to do nothing just curious for future reference.
     
  2. Patrick Sun

    Patrick Sun Moderator
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    Whatever the straight port length is, when using a flared port kit, add 1" to the straight port length to get to the final end-to-end flared port kit's length.

    So in the case, you'd want to use the entire flared port kit's length of 18".
     
  3. Adam Demuth

    Adam Demuth Agent

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    I'm going to be using PVC for a port, and it will need to have a 90 degree angle, how do I measure around the curve?
     
  4. ThomasW

    ThomasW Cinematographer

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    Angles in ports should be avoided if possible (They change the tuning slightly). Look at relocating the port if that's an option.

    Otherwise just measure through the middle of the elbow
     
  5. Adam Demuth

    Adam Demuth Agent

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    I was afraid of that. You just had to go and make things difficult for me... [​IMG]
     
  6. ThomasW

    ThomasW Cinematographer

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    Don't worry about it. The changes would likely be measurable with test gear, but are probably inaudible.
     
  7. Troy R

    Troy R Stunt Coordinator

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    I have a question about the 4" vent kit. I bought the 4" flared Precision Port from Parts Express but no where in the installation instructions does it say how big of hole to cut to get that flared end mounted. So what diameter hole do I need to cut for the port?
     
  8. Patrick Sun

    Patrick Sun Moderator
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    Seriously, use a ruler and figure it out. Just don't make the hole so big that you don't have any material to screw the port into the MDF. You might want to make the hole slightly smaller where the curvature starts on the flared edges (and simply do a little sanding to get the flared edges to seat properly).

    Also, if you have a piece of scrap MDF, practice on that as well.
     
  9. Troy R

    Troy R Stunt Coordinator

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    I've done that, I just thought I would ask! I'm sure there are people on the board that have used this product before and could EASILY help me make sure I got it right the first time...
     
  10. perry web

    perry web Stunt Coordinator

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    the mounting flang of the port is 7.25. The flat part of the flange is 1/2". So 7.25 - (2 x 1/2) = 6.25"

    you can make the hole smaller if you chamfer or radius the edge has mentioned about but the out side point will still be roughly 6.25"

    I wanted to mount mine w/ threaded inserts so I can remove it easily but there was not enough material so I just used silicon and self tapping screws. When I paint I will just tape it off.
     
  11. Patrick Sun

    Patrick Sun Moderator
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    I did more work on mine, I made the hole 5" wide, and then sanded the opening to mate with the flared port piece. By doing it this way, I had some MDF to work with to add screw holes for the flare.

    Check out photos 95-98 in this page.
     

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