port opening too close to driver/tube wall/endcap?

Discussion in 'Archived Threads 2001-2004' started by Jeff Meininger, Sep 7, 2002.

  1. Jeff Meininger

    Jeff Meininger Second Unit

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    I'm trying to design an EBS shiva using 20-inch diameter sonotube. I'm trying to avoid porting out the top because I'd like to have the option of using the sub as a small table. If I have to port out the top, I can always use a "baseplate" on the top, but this adds a good 4 inches to the height.
    I'd like to use an FP4 flared port kit as the adire spec calls for, but this page (http://terryctheater.tripod.com/shiv...bum/page1.html) makes me wonder if I'll be able to make it fit along with the driver on the bottom plate. If it will fit, it's certainly going to be a close fit. But going up to a 5" port isn't feasible because tuning to 18 Hz would require the tube to be too long to fit comfortably inside the tube. I think there would be about two inches between the port opening and the endcap. I've read that you need at least 3.
    So if the port opening on the bottom is very very close to the driver, and the edge of the flare is very very close to the tube wall inside the sub, am I still okay? I'd like to save myself the 4 inches, but not at the expense of sound quality.
    Thanks!!
     
  2. Ron D Core

    Ron D Core Stunt Coordinator

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    I don't think it would hurt anything, but I'm no expert. Maybe you can go with multiple smaller ports. Is the option of constructing your own port out of the question?
     
  3. Jeff Meininger

    Jeff Meininger Second Unit

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    Multiple ports must be longer, though, since the surface area is doubled. One 5-inch straight port will just barely fit, and two non-flared 4-inch ports would have to bend a couple times to fit. [​IMG]
    I'm estimating my results based on measurements of 12.25" for the shiva, and 7.25" for the FP4 or parts-express 4" port flare kit.
    I'll have about 2 mm between the driver and port on the bottom endcap, and about 3 mm between the port opening and sonotube wall inside the sub. That's a pretty tight fit indeed! That means that the port opening will be interacting with the poly batting on the sub wall, unless I don't put any batting by the port opening.
    I'm also concerned about possible driver/port interaction. On most sub designs I've seen, the driver and port are at least 2 inches away from eachother, many times they're even further apart. Maybe this is for aesthetic reasons, but maybe it isn't?
     
  4. Patrick Sun

    Patrick Sun Moderator
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    I used a flared 4" port with a 15" Tempest in a 24" wide sonotube (all mounted on the bottom endcap). I didn't really come across any strange anomalies from the configuration that detracted from its performance. This was Sunosub III.
     
  5. Jeff Meininger

    Jeff Meininger Second Unit

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    That's reassuring, Patrick, thanks! I guess it's full steam ahead with my plan then. [​IMG]
     
  6. Dustin B

    Dustin B Producer

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    Have you considered a pair of 3" flared ports. A pair of 3" flared ports shouldn't have length problems, have a little more cross sectional area than a 4" port and will have a smaller flange radius.
     
  7. Patrick Sun

    Patrick Sun Moderator
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    Might be tough to fit two flared 3" ports (probably takes up circles of 6" in diameter with the flares)on the bottom endcap with the 12" driver in a 20" wide sonotube.
     
  8. Brian Bunge

    Brian Bunge Producer

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    Pat is correct. The 3" ports take 5.25" through holes and the outer flange is actually 6.25" in diameter. It might work but if so it will be mighty tight down there!

    Brian
     
  9. Dustin B

    Dustin B Producer

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    I was going off that pic he linked to in his first post. Put a 3" flared where the port in that picture is and the other 3" flared where the binding posts are. Then use those screw through binding posts like I did on my twins (take up very little space).

    The 3" flared ports have a 1" smaller flange and hole diameter which should make for a not so tight fit. Mind you, you won't have much endcap material left though :p)
     

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