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Is there a formula for cabinet porting?

Discussion in 'Amps and Cabs [BG]' started by Stinsok, Feb 20, 2003.

  1. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Considering building a 2/10 or 2/12 cabinet, and wondering about proper porting. Any ideas.
  2. BruceWane


    Oct 31, 2002
    Houston, TX
    Yep, there are formulas to use. Do a little research on Thiele and Small, a couple of scientists that did extensive work on this stuff; they established the mathematical science behind ported cabinets. You'll need the thiele-small parameters for the speakers you plan to use, as well as the internal volume of your cabinet.

    Download a program called WinISD - it'll do the calculations for you.
  3. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Thanks for the help!
  4. Vented (Port) Enclosures

    Vb = 15 * Vas * Qts2.87

    Fb = 0.42 * Fs / Qts0.9

    F3 = 0.26 * Fs / Qts1.4

    db = 20 * log10 [ 2.6 * Qts * ( Vas / Vb )0.35 ]

    VentArea_sqin >= 0.02032 * Fb_hz * Vd_cuin

    The origin of this relationship is Richard Small's excellent paper on vented boxes:
    "Vented-Box Loudspeaker Systems Part II: Large Signal Analysis" Journal of the Audio Engineering Society, Volume 21, Number 6 July/August 1973
  5. ESP-LTD


    Sep 9, 2001
    If you don't know, just say so .... :D
  6. You could also do a search on "DIY speaker building" it turned up some link pages that had on-line calculators. They are not as flexible as winISD (and it's free) but the will give you an idea. If you need speakers try Parts Express or Madisound, but they focus more on Hifi. also check out the eminence web site, they publish all of the Theile/Small specs for their speakers there.

    Have fun.
  7. I recently built a pair of ported subwoofers with speakers and accessories from Parts Express. The nice folks at Parts Express had the software to give me venting information. All I had to do was ask. I also recommend Part Express because my corners, handles, jack plates, port tubes, and covering look terrific and were pretty cheap. Including generic drivers made by Eminence (which were on closeout special), I built the subs for less than $200 each! They look like my SWR stuff other than the grills, which I already had. -Wes
  8. Parts Express is a good source for many parts. If you are going to buy more than $50, look into:


    As they are the supplier of many cabinet parts, etc, to Parts Express. The price at Penn is a WHOLE lot better, if you are buying in bulk. I buy grilles, feet, corners, wheels, carpet, etc from Penn and the price is much better. They are very fast shipping, and OK for non-wholesale (public) buyers. They do have a $50 minimum order.
  9. Here's my version of the formula, quoted from an ancient thread "cabinet building 101" (you should read that thread, BTW)