Port length for shiva?

Discussion in 'Home Theater Projects' started by DorianBryant, Nov 27, 2004.

  1. DorianBryant

    DorianBryant Screenwriter

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    I built a 85 liter Shiva with a 4" port. I must have ordered the wrong port from Parts Express or they sent me the wrong one. The one I received is 11.5" totall length and flared on both ends. The numbers i came up with indicate the port length should be 13.87" to tune to 20-22 hz.

    Does this sound right? I tried the 11.5" port but it seems to be a bit boomy.

    Should i get the longer port? I tried to plug the port but it really effects the output. It somewhat tighter though.

    What length 4" port should i be using?
     
  2. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    Sounds like they sent you their clearance 3" x 11.5" port. I would send it back and have you send the correct 4" port because that's what you paid for or refund you the difference. That said, the 3" x 11.5" port is giving you a tune of around 21.5hz which should give a prety gradual rolloff w/ an F3 of around 25hz. What you're perceiving as boominess is probably due to room peaks or nulls. I would experiment with placement to see if you can minize this, or it may be neccesary to add some kind of EQ to combat the peeks.
     
  3. minhG

    minhG Stunt Coordinator

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    just to be clear, is that 11.5 with the flares or only the center section?
     
  4. DorianBryant

    DorianBryant Screenwriter

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    Actually it is a 4" port with flares on both ends and a total length of 11.5".

    I have gotten conflicting results from a couple of different programs. Thought I would pose the question to those in the know. Since the hole is cut, what length 4" port should i use to get down in the 20's? Does 13.87 sound reasonable?

    I may look into an EQ. Most seem to be using the BFD.

    I was also using a 120watt RMS amp which may or may not have a bass boost. I sold it and will be getting a 250 watt amp from PE without a boost.

    when i demoed the sub upstairs in my living room i played around with placement but was getting some serious resonance from the windows. I want to get the port length and amp straightened out first.

    Thanks for the help.
     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Not particularly. I assume you mean 13.87 inches TOTAL (including flares). This would get you to around 26-27Hz tune with about 1.5dB bump around 40Hz.

    In 85L even using the full 18" length of the 4" flared port you'll only tune it down to about 23-24Hz. So I'd want to use at least this much. And perhaps you could mate some other 4" tubing to the flares to get more length. You'd need 25-26" total to achieve the "Adire alignment" and get 20Hz tune.
     
  6. Dennis Gardner

    Dennis Gardner Stunt Coordinator

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    It took a 19" long 4" port to get a 17 hz tune for my 142 litre box. I run dual Shivas with 320 watts.
     
  7. DorianBryant

    DorianBryant Screenwriter

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    yes, 13.87" inclusing the flares. 11.5 seems just too short. hopefullt this, and a better amp will allow me to ge the performance I am looking for.
     

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