Flared ports vs. unflared ones. When can I get away with unflared?

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Dec 8, 2002.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    As my quest comes almost to an end, I find out that all I'm missing now is the port material / configuration.
    I saw at PartsExpress that a flared port could give me 3dB extra output over an unflared one. OK, that sounds a bit over the top to me.
    I was thinking about using unflared (ie, PVC) tubing for my subwoofer, a 170 liter box tuned at 18 hz. I'm getting a 14.5" long, 4" diameter port in order to get a nice airflow.
    Will I *really* be losing those 3dB if I use PVC instead of a flared port? What exactly am I ganinig by spending the extra dollars in a premium port?
    I'm asking you because I can't find a flared port around here, and PE would charge me $75 to send a pair of 4" flared ports to México. Compare this to the... hmmm... $2 I paid for 1 meter of PVC piping, and you get the idea. [​IMG]
    Thanks!
     
  2. Dustin B

    Dustin B Producer

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    I remember reading from one of the more knowlegable here that flared ports don't gain you anything over a straight port until the air speed passes 17 m/s. So to be simplistic I guess you could say, if the air speed stays under 17m/s, a straight port will be just fine.
     
  3. Chris Carswell

    Chris Carswell Supporting Actor

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    Do you have a router? If so make your own like I do. I use a 3 1/2" hole saw to cut a hole in a 5" square piece of MDF. If you don't have a hole saw or jaser jig for your router you can slowly cut a hole using a jig saw. Now that you got your hole, push the 3" wide PVC in until it is flush. Then take a 1/2" or 3/4" round over bit & round over the inside of the PVC. Glue the MDF to the PVC. Inside part is done. Now do the same for the outside except just cut the hole in the cabinet where you want to port to go(no additional square piece is needed). You just saved $73.
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Thanks, Dustin. I'll try and model someting on WinISD that will keep airspeed *below* that threshold, just in case.

    Chris, I saw your idea before in this forum, but I couldn't understand how to do it. Now I get it! You are basically flaring the wood using the PVC as the tube. It's not a bad idea - maybe I'll try it.

    I also found out that the size of the ports differs greatly when using flared and unflared ports. Is this correct? For example, when using the PE3 Flared Ports for Adire Alignment's design, the tube length is given as 11", if I recall corectly. When simulated on WinISD or LSPCad, I get a 14" tube. So, if I decided on going flared, how could I simulate it using a commercially available software?

    Thanks for your input!

    Thanks a lot!
     
  5. Greg Monfort

    Greg Monfort Supporting Actor

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    Right DB, ~5% mach, or ~56.5ft/sec (17.2m/sec). If downfiring into carpet then you can often go as high as 10%.

    I find a 3dB difference hard to accept based both on theory and my own simple measurements. If vent mach is so high that it compresses its potential output 3dB, then the flare rate would have to be a lot greater than what the flared tube kits offer AFAIK.

    GM
     
  6. Keith Martin

    Keith Martin Auditioning

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    The 11" length Adire is referring to is the only the TUBE length. That's not accounting for the length that's in each of the ports. So overall port length is very near the same for flared and standard. This from experience using BassBox Pro.
    BTW, I don't think simply rounding over the edges of the port is considered a true flare. It is slightly helpful in reducing the chances of port noise but I'd keep the original overall length of 14" and round over.
     

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