Dual Tempest & LspCad - can this be right?

Discussion in 'Archived Threads 2001-2004' started by Tyson Neidig, Feb 16, 2001.

  1. Tyson Neidig

    Tyson Neidig Auditioning

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    I input all the #'s for box size, fill, resonant frequency, etc. . . then I hit the optimize option to find out what port size & lenght I need to get a tune of 19hz out of my 750liter box with 2 front firing tempest drivers. It tells me that I need a port that is 2.9 centimeters long & 8.9 cm in diameter? Surely this can't be right. . . . What am I doing wrong?
     
  2. DanWiggins

    DanWiggins Second Unit

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    Tyson,
    For 750 liters and twin Tempests, I'd look at a tuning closer to 17 Hz or so. Use a 10" diameter vent, and you should be set for 700W or so... [​IMG]
    Note that the optimizer will optimize for a box volume AND tuning. I don't think it plays with vent diameter, other than cranking it up to make a realizable vent length for a given tuning.
    Dan Wiggins
    Adire Audio
     
  3. Tyson Neidig

    Tyson Neidig Auditioning

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    Thanks a bunch for the reply Dan - I am helping a friend put this project together - he wanted the ultimate bass possible for under $1k & I told him the Tempest was it! So, regarding port length, when I run the 17 hz tune for a 750 liter box, it tells me that port length should be 10cm? That is like 4 inches. Seems like everyone else is using 20-30 inch ports to get the right tune. Am I doing something wrong with the program to give me such a short port length? When I play around with box and port settings manually, I still get some odd readings. I put in the 750l volume, fill of 50%, and a port length of 20cm. This gives a tune of 10.5hz. If I manually change the tuning to 17hz, it puts the port length at 3.7cm. My only guess is that I am using LspCad incorrectly. But everything seems to be filled out properly, since the tempest comes pre-loaded & I did not make any changes to the T/S parameters. Any idea what I am doing wrong?
     
  4. Poul Nielsen

    Poul Nielsen Auditioning

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    I don´t remember the formular, but with regard to tuning, the rule is, the larger the box, the shorter the ports.
    750 l is a truly massive box, so the port lenght is probably ok. Now, are you sure you want to build such a large sub? I have just built a 270 l single tempest sub (haven´t put in the driver yet, so ask me later how it sounds...) and it is a pretty large piece of furniture. I can´t even imagine where I would put one three times as big...
    Eventually you reach a point, where an increase in box size is just not worth it, performancewise. IMO a box approx. 4-500 l would perform just as well as the 750 l one.
    My 0.02$
    Best regards,
    Poul Nielsen
     

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