Port Question

Discussion in 'Home Theater Projects' started by Mike Strassburg, Apr 28, 2006.

  1. Mike Strassburg

    Mike Strassburg Second Unit

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    My old sonotube had (2) 6" x 22.5" ports. I'm going to throw a few Tempests into a ported box, same volume as the sonotube, but will be using 8" ports as they're much easier to find and cheaper.

    I used a basic volume calculator and it comes up with a 8" x 12.75" being the same as the old 6" port. Is there any problem with running (2) of those 8" ports? Is there an ideal diameter to length ratio to avoid chuffing, but still make the port work properly??

    Need help from the port gurus!!! TIA...Mike
     
  2. Patrick Sun

    Patrick Sun Moderator
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    Something must be off because the larger the port diameter, the longer the port needs to be (keeping internal volume the same, and tuning frequency the same).
     
  3. Mattak

    Mattak Stunt Coordinator

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    It's not very clear...he said one 8" port whereas his old had two 6" and then asks about two.

    One 8" port per tempest is plenty IMO. You want to look at port area when considering what size to go with. An 8" port is about 50sq inches and should be more than enough for a tempest. If anything you could also take a 1/2" roundover bit to the edge.
     
  4. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    This is the problem. He thinks equal port volume means equal tuning. This is certainly not the case. An 8 inch port has 78% more port area than a 6 inch port. So the length needs to be 78% longer to maintain the same tuning.

    Two 8 x 40 ports would tune to the same frequency as two 6 x 22.5 ports.

    Its also possible that his old sonotube housed 2 Tempests - one on each end.

    Mike - chuffing is dependent on the total cross-sectional area of your ports (and the amount of air your woofers are moving). Tuning is dependent on the size of the box and the ratio of total port cross-sectional area to port length. And no, two 20 inch long ports are not the equivalent of one 40 inch port. Both ports must be 40 to achieve that tuning.
     
  5. SteveCallas

    SteveCallas Second Unit

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    Plug your parameters into WinISD so you can take out the guess work. In addition to the correct lengths, it will track the first port resonance for you. I aim to keep my first resonance above ~220hz, but others have heard no audible effects with letting it get as low as 180hz - I wouldn't feel comfortable letting it drop any lower than that.
     

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