Bandpass Speaker Box Design (Fourth-Order)

Fourth-Order Bandpass Enclosure Design Calculator
Explanation of Terms Used
Qts, Vas, and Fs, are the electro-mechanical parameters for your woofer. They are also commonly referred to as the "Thiele-Small" parameters. You can get these from the paperwork that came with your speakers, from the dealer where you purchased your speakers, or from the manufacturer of the speaker (they are sometimes hard to contact, however).
S Factor - refers to the efficiency of the enclosure. 0.7 is the most efficient, however, it also has the narrowest passband. 0.5 is the least efficient, but it has the widest passband. One of the reasons bandpass enclosures are so popular is this inherent property that allows the designer the flexibility to trade bandwidth for efficiency or vice versa.
F3(L) - the frequency where the response is down by 3 dB (on the low end of the passband). This will be the first number in the "Passband" box when you calculate an enclosure.
F3(H) - the frequency where the response is down by 3 dB (on the high end of the passband). This will be the second number in the "Passband" box when you calculate an enclosure.
Vf - the internal volume of the front (vented) chamber of the enclosure.
Vr - the internal volume of the rear (sealed) chamber of the enclosure.
Qbp - is the total resonance of the speaker system.
Fb - the frequency that the vent in the front chamber of the enclosure needs to be tuned to.
Passband - refers to the range of frequencies that will be allowed to pass through the speaker system (the frequencies you will be able to hear/feel). Any frequencies above or below the passband will be attenuated (reduced).
Gain - the amount of boost(or in some designs the amount of attenuation) in sound pressure level(SPL). This is usually referred to in speaker design with other terms, which serve to make it a valid reference point.

A typical specification for a bandpass enclosure would be :

Efficiency/Sensitivity : 94 dB SPL @ 1W/1M.

 This means that this design is capable of creating a sound pressure level of 94 dB when a signal of 1 watt is applied to it, and is measured with the measuring instrument 1 meter (3.28 feet) away from the speaker system.
Bandpass Enclosure Image

Typical Fourth-Order Bandpass
Enclosure Design  
Calculate Your Enclosure Here
 This calculator will design an enclosure using any value for F3(L) that you desire. If the "Gain" value comes up negative, you will have to increase the value you entered for F3(L), or choose a higher S factor.

Note : Too much gain can be hazardous to your speakers, try to keep it +3 dB or less unless you want to find out what your speakers look like with holes in them.
Number of Drivers 
Isobaric Loading
Yes  No
  
Enter Qts
Enter Vas  (ft3 )
Enter Fs
Choose an S Factor
0.7  0.6   0.5
    		 Enter Desired F3(L) 
Vf =(ft3 )
Vr = (ft3 )		 Qbp = 
Fb = Hertz		 Passband =  Hertz
Gain = (dB SPL@1W/1M)

  If you want to experiment with different quantities of drivers, or the isobaric option, you don't need to enter all of the values again, just change the value you want to adjust and click the "Calculate Enclosure" button again. When you are finished, write down your enclosure specifications, (or copy & paste them), and go here to design the port(s) for your front chamber.