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Where to aim a port

Discussion in 'Home Theater Projects' started by Kevin_W, Jun 8, 2004.

  1. Kevin_W

    Kevin_W Second Unit

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    Hi,

    I have what I am sure is an easy question. I am building a ported enclosure for my car but due to space limitations its going to be rather long and narrow. Can I use a PVC elbow so that the port opening is on the same side as the driver, or does this not matter? In other words can the port can be on any side of the box?

    Thank you,
    KW
     
  2. GrahamT

    GrahamT Supporting Actor

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    It doesn't matter where it goes
     
  3. Kevin_W

    Kevin_W Second Unit

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    Thanks!

    And as long as I am keeping the port tube the proper length overall, a 90 degree bend inside the box is fine correct?



    KW
     
  4. Andrew Pratt

    Andrew Pratt Producer

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    Yes that's correct...just make sure its well glued so it doens't rattle at some future point (happened to me on the one and only bent port I used)
     
  5. Kevin_W

    Kevin_W Second Unit

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    Thanks again!

    Just as a side note, how much room for error does one have with port lenghts? For instance I know for the driver and enclosure I am going to use, the port is to be 3" x 16.5". If for some reason the tube actually ended up being 16.75" or 16.25" because of something I screwed up, how much does that affect the overall performance?

    KW
     
  6. Geoff L

    Geoff L Screenwriter

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    Depending on box size, (a large box or tubes internal volume) it can make a bigger difference than in the case of a smaller box which would make a minor diference.

    In general, 2 to 3cf^³ it should make a minor difference in the tune, say a HZ or so one way or another at most.

    If this is a really big deal for you,
    post your box volume & we an tell you exactly what the difference might be using the port info you provided..

    Just go a little long on the port and test it, then you can remove some port length if you want the tune higher....

    Hope that helps
    Geoff
     
  7. Dave Poehlman

    Dave Poehlman Producer

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    I've read that a good rule of thumb is to keep the port 1 diameter length away from any box walls or driver holes, and not to place it directly behind the woofer. But, this is more for an even airflow issue rather than tuning.

    In fact, it's not necessary to put the port in the box. You could have it sticking out of the top like a big stovepipe if you want! [​IMG]
     
  8. Andrew Pratt

    Andrew Pratt Producer

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    If you run the sims you'll see half and inch one way or the other won't make any real world difference at all...in fact you're likely going to be slightly off on the true internal volume anyway with all the bracing, driver and port unknowns so its likely not an issue worth worrying about....esp in a car environment were you're going to get so much cabin gain anyway.
     
  9. Kevin_W

    Kevin_W Second Unit

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    Cabin gain... I wish [​IMG]

    Thanks for the tips... In fact I might just put some of the port outside to use as a "natural" fan over the amp.

    The box is going to be 1.6cf^3 (this accomodates for drivers displacement). Slightly larger I think because I'll have to build a brace inside (it'll be getting 500w RMS and the box has to be long and narrow due to my application).

    But, now that I have a couple people reading, I'll whore myself out for another very important question. :b

    This 1.6cf^3 box is for my driver. The 10" driver specs are:

    Fs: 29.9
    Re: 3.7
    Qms: 9.0
    Qes: 0.422
    Qts: 0.404
    Vas: 28.46l
    Mms 168.36g
    Cms: 168.4
    BL: 16.64 Tesla-M
    SPL: 85db 1w/1m
    Sd 345 sq cm
    Xmax (Field); 35mm p-p
    Sub's displacement I'm told is .1cf

    The original specs that are in the white papers state a 1.1cf^3 (includes displacement) box with a 2" x 9.5" port. This is their "sound quality" setup (versus their SPL specs). However these specs are a year old and they are now saying go with the 1.6cf box with the 3"x16.5" port. Lemme just tell you that this is going into the cargo space on a Wrangler. A 1.6 box will eat up most of the room. From a pure *speculation* standpoint, and based on the parameters I've listed, does it appear that the 1.6cf is going to give me a noticeable increase in output? If not, I will stick with the 1.1cf box and save the room.

    Thoughts?

    Kevin
     

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