Shavano Music Online

    Sub Woofer;
    4th Order Bandpass Calculator

    5/98 - Jens Moller - http://www.colomar.com/Shavano/4thorder_info.html
    text updated 3/02
    Many people have asked for information on building their own Sub-Woofer systems. In some ways, it appears to be a black art (I have the 5th Edition of the Loud Speaker Design Cookbook, by Vance Dickason, and its not as simple as I would want it to be. You may wish to purchase this book and learn a lot more about driver design and enclosure effects) - there are numerous issues to contend with.

    To simplify matters somewhat, I used equations found at:

      http://www.diysubwoofers.org/

    and created a CGI program that takes a number of parameters and generates the results based on these equations for a 4th Order Bandpass Box.

    Please be aware that you really need to add a First or Second Order Passive Crossover (which would make this into a 5th or 6th Order Bandpass box); or, you will have to have a separate power amplifier that has an active crossover for this cabinet that restricts the frequency response accordingly (4th Order Bandpass cabinets have very uneven frequency response at frequencies above the Sub-Bass range (200 Hz or more) - you will need to manage this with either a Passive or Active Crossover network).

    See: First Order Crossover Networks and Second Order Crossover Networks for information about adding one to this box.

    Also see Additional information about this application and its use.

    Please fill in the following Information. 

      Construction Data
       Diameter:  Speaker Diameter in Inches
        Bracing:  (Optional)
      Thickness:  of cabinet material
  Speaker (Driver) Data
            Qts: 
             Fs:  (Hz)
            Vas:   
  Cabinet Parameters
              S: Response Curve
             F3: Hz - Low Freq Roll-off
  Port Diameter:  (Optional)
    Note: Enclosures with an S (Response Curve) value of 0.4 will be the smallest in size, have the widest response range but will have a dip of approximately 2.7 db in the middle of the response curve. An enclosure with an S (Response Curve) of 0.7 will have a larger box, narrower response range, but will generate a flat response curve.

    Optional: If you have a specific Port material that you want to use, and you know the inside diameter in inches (ie. 1 3/4 inches = 1.75), or in mm, you may enter this value manually. Select the right scale to use. This value must be entered as a decimal value (the program does not understand fractions).

    Disclaimer: I've checked the results from this application against another application that generates 4th Order Bandpass information, and while the results differed moderately, there were no significant errors in the data generated when comparing both results. Your results may vary.

    This software generates results for a single speaker. You may consider adding a second speaker to your system, if you do, all parameters stay the same, except Vas. Assuming identical drivers:

    • For Isobaric (Push-Pull) - Vas gets divided by 2 and the speakers are wired out of phase. Make this correction to the Vas parameter you enter before calculating your results.

    • For 2 separate drivers mounted in the Sealed enclosure (this program doesn't generate results/drawings for this design) - Vas gets multiplied by 2 and the speakers are wired in phase. Make this correction to the Vas parameter you enter before calculating your results.

      You can define the Diameter parameter as the the size of both the drivers put together - ie. 2 6 inch speakers = 12 inch Diameter. Make this correction to the Diameter parameter you enter before calculating your results.

    Also be aware that the published specifications of your Speaker is based on a sampling of the production run. Large variations may exist in any 2 speakers produced by the same manufacturer with the same model number. This is not as big an issue as it could be. The relationships of the major parameters tend to be quite consistent and while it could impact your design, it may not be significant. If in doubt, there are systems that can be used to individually measure speaker parameters available from Parts Express and LinearX (and others) using a Windows based PC.

    Note: The Results generated here should work for any Subwoofer use: Pro-Audio sound re-enforcement, Car Audio or Home Audio. Most Pro-Audio systems have higher SPL values associated with the drivers - they are also typically driven harder to cover a larger area. The addition of Acoustic fill may be necessary. For Pro-Audio use, you should use at least 2 Subwoofers placed 10 feet or more apart to cancel standing waves. Also, consider that the Subwoofer can absorb sustantial amounts of power; it is in your best interests to over rate the capability of your Subwoofers by at least 50% - for example, if you have a 200 watt per channel Power amp (at 8 ohms, for example), you should use Drivers that are capable of 300 watt transients at the same impedance the Power amp will be operating at. Multiple drivers may be required to accomplish this.

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