If I have the calculations for a bandpass enclosure, can I simply multiply them by 2 if I want an additional subwoofer?

I have 2 identical 12 inch subwoofers. I have the measurements from the company for a bandpass enclosure, but the box is only meant to house one driver. I want to build ONE box but have BOTH subwoofers in it. Would I simply multiply all the measurements by 2? Would I need to do anything with the port dimensions? Or would I just be able to dual port it? Or is there some other steps that I have to do. Here are the measurements just in case any one wants to see them:

(Vf) Box Volume - .84 Cu. Ft.
(Vr) Box Volume - .91 Cu. Ft.
(P) Port ID - 4"
(P) Port Length - 4.25"


Width - 15"
Height - 20.75"
Depth - 15"
(Sb) 9.25"


Vf (Front Chamber (Ported Section))
Vr (Rear Chamber) (Sealed Section))
Sb (Speaker Baffle Location (Vf's height)

Any help would be much appreciated. 


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That all depends on how you want to mount the speakers and how you want to build the box(es).

The easiest way is to build 2 boxes and make the face, back, bottom, and top all one piece (2 x's the length). Just make sure that they are separated between the individual boxes by some sort of partition. That way you are pretty much guaranteed that things will work correctly.

If you wish to make the speakers actually share the space inside the box, you have 2 options there, compound or isobaric. Compound is when you place the speakers (drivers) on the same face, normally side by side. in this case, your Qts stays the same, but the Vas doubles. When you do Isobaric, the speakers are usually placed face to face and are wired out of phase so that when the rear driver pushes forward, the front driver pulls back, thereby making both move in the same direction. In this case, Vas stays the same but Qts is halved.

If either of these is the way you want to go, you would need to calculate a new box for that configuration. Give me an idea of what you are thinking and I should be able to help you arrive at a solid bottom end.

brandencota (author)  Quercus austrina6 years ago
Thanks a lot. I'm going to go with option 1. I never thought of that before. (I would give you best answer, but I don't know how to take it away from the other guy...)
brandencota (author)  brandencota6 years ago
NVM about the best answer thing...
Best answer!

Thank you American Eagle and thank you Re-design, that is quite the compliment. I have been exploring building speakers and actually building them since I was a young teen ( good god, has it been that long???!!!;) ).

Most of my expertise came from reading Popular Electronics - the William R. Hoffman series of articles -  and books from Radio Shack, back when they actually had replacement / hobby speakers on the shelf / in stock. One was from the 80's by W. B. Weems (and some other guy) and a book from the 70's that I found at a yard sale - also a RS book. I'll have to dig them out to let you know the actual names. That and good old trial and error.

All that reading gave me a good grasp of the calculations needed and I did many by hand on my TI30X. I even used the calcs to rebuild a friend's Bose 401's (first gen from the 70's) and he couldn't believe how much better they sounded when they were completed (Pioneer drivers ROCK!).

American Eagle, I look forward to helping you learn this rewarding hobby.


Re-design6 years ago
The vol. should be double or somewhere between 1.5 and two.  The vol is not as critical and the port shape and size.

The port size and shape should remain the same since it's tuned to a specific frequency not speaker.