help me figure internal volume with these parameters

Discussion in 'Archived Threads 2001-2004' started by rodneyH, Aug 4, 2002.

  1. rodneyH

    rodneyH Supporting Actor

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    I have a spare SVS standard driver, and a very nice end table (cabnet) that is enclosed, I am thinking about building a box a dropping in right in the end table, so it looks very nice. It looks like I could drop a box in with the internal volume of about 3.25 cubic feet (internal dimensions of the sub box would be about 20"WX17.5"HX16"D (which should equal about 3.24 if my math is corrrect). Cane someone tell me if I would need a port?, if so how big of a diameter, length?, how much poly fill to put it? (I am a beginner at this and don't understand tuning, while some of you appear to be GREAT at it, I don't want to screw it up). I would assume I want it tuned to 20 or 22 Hz if possible.

    here are the dimensions of the SVS driver

    SVS Stats:
    ----------
    FS- 21 hz
    Qts- .38
    Qes- .39
    Qms- 6.6
    Vas- 4.6 ft^3 or 130 liters
    Z Impedance- 4ohms
    Re- 3.2ohms
    SPL- ~87dB
    X-max- ~14mm
    power handling- ~200w
    ---------------------

    sorry if it is a stupid question and thanks for giving me help!!

    also,the driver will face down, is that the same direction the port should face?? any other recommendations are much appreciated
     
  2. Adam Bluhm

    Adam Bluhm Supporting Actor

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    I just posted in somewhat of a related thread. I have WINisd, but that's a bit confusing. I want to begin working on a single ported Shiva sonosub.
    I'll begin doing a search for this program you speak of and mess with that some. [​IMG]
    «edit»
    I don't have excell. Unibox is a nogo. [​IMG]
     
  3. rodneyH

    rodneyH Supporting Actor

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    John, what if I increased the size to 3.56 cubic feet??

    is that a differance enough, and what would I be at then if it was sealed Vs ported???
     
  4. rodneyH

    rodneyH Supporting Actor

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    yep, the program didn't work for me either
     
  5. Patrick Sun

    Patrick Sun Moderator
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    You could simulate a SVS 25-31 (tuned to 25Hz, total sub height around 31", just a bit over 85-88 liters, 3 ft^3) with the existing enclosure, and use a 4" wide port roughly 13.5" long (if you use a flared port kit, make the end-to-end length 14.5").

    If you wanted to tune it a smidge lower (around 22-23Hz), use a 4" wide port 17" long (which is perfect with a flared port kit because that's the usuable length of the kit), with the volume around 3.5 ft^3.
     
  6. rodneyH

    rodneyH Supporting Actor

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    Patrick, would I have to make the cabnet 31" high, because the space I was thinking about using is only about 17.5" high (on the inside). Would that make a difference???
     
  7. Patrick Sun

    Patrick Sun Moderator
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    I just provided the SVS "model number" as a comparison to what you might expect in terms of performance. All you should worry about is internal volume, not a specific height dimension value.
     
  8. rodneyH

    rodneyH Supporting Actor

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    patrick, so for a FINAL word (in other words, I will build it based on these dimensions), If I get 3.5 cubic ft and use a 17" long 4" diameter port, it should go 22-23 HZ?

    1 final question, does the port have to be straight, or can it curve??
     
  9. rodneyH

    rodneyH Supporting Actor

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    opps, a couple more

    1.how much poly fill do I use??

    2.do I face the port and driver down or does it matter??
     
  10. Patrick Sun

    Patrick Sun Moderator
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    Straight ports are preferable. If you have to use a curved port, use the center line length as its length.

    Umm...polyfill - anywhere from none to around 50% fill (100% fill means 1 pound per cubic foot) which is up to 1.75 pounds of polyfill for a 3.5 ft^3 enclosure. Try it with none, it is sounds good, don't use any polyfill. If it's a tad boomy, stuff some polyfill inside and listen again.

    Driver/port orientation shouldn't matter as long as both don't have any obstructions in their way. (Don't point a front firing sub into the way, for example).
     
  11. rodneyH

    rodneyH Supporting Actor

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    OK, another question.

    is it OK if the inside port hole is ONLY 1.5" AWAY FROM THE inside of the cabnet (top)?? (if that makes sense)
     
  12. Patrick Sun

    Patrick Sun Moderator
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    You need roughly 4" or more of clearance for the hole, otherwise, you run the risk of introducing chuffing sounds from the port during loud bass passages.
     
  13. rodneyH

    rodneyH Supporting Actor

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    dang, now I am back to square 1.

    a couple more questions

    crap, I forgot to figure in the volume of the drver and the port? how much of the 3.24 OR 3.56 cubic feet will that take up???


    1. If I build the box 3.24 cubic ft (then mius the volume of the driver and port) what will the tuning frequency be if I use the 13.5" length and 4" diameter port?

    2. If I build the box 3.56 cubic ft (and minus the volumes) with the same port, what will the freq be??

    THANX FOR ALL YOUR HELP!!!!
     
  14. Patrick Sun

    Patrick Sun Moderator
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    The tuned frequency will most likely move up by 1Hz-2Hz if at all. You can put in some polyfill later to make up the volume lost to the driver/port. These are little details, just build the sub!
     
  15. rodneyH

    rodneyH Supporting Actor

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    Patrick, I am really close to finalizing the plans, so I hope to build it very soon.

    in your opinion, would you go for the 3.24 or the 3.56 cubic feet (the 3.56 will require some slighlty more work, but if it is going to make a huge diffference, I will do it.
     
  16. Patrick Sun

    Patrick Sun Moderator
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    If it's a lot of work to get an extra 1/4 ft^3 of volume, rely on using polyfill then.
     
  17. rodneyH

    rodneyH Supporting Actor

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    sounds good, thanks for the advice, perhaps I will try and download one of the programs you recommended on another computer to see if it will work.
     

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