Subwoofer Formula?
Dear Gary: My name is John Fairbanks. I am with Brock Audio/Video Systems in Beaumont, Texas. I always enjoy reading Terry Paullin’s column in Widescreen Review. I particularly enjoyed the column on “Affordable Home Theatre.” Most of the systems that we do fall into this category—with a few notable exceptions. In the article, Terry alluded to a formula for finding the right size subwoofer for ANY system. I have been looking for such a formula for a while. Would you possibly share this with me or point me in the right direction? I really would appreciate it. Thanks in advance—and continue Terry’s great column!
John Fairbanks, Brock Audio/Video Systems, Beaumont, Texas
Contributing Editor Terry Paullin Comments:
Thanks for the kind words; it’s always very satisfying to hear positive feedback from readers. No, I don’t use a specific formula, but I’m confident that with a little bit of time, a calculator, and about ten subsequent jobs to verify real-world results, one could be arrived at, since room dimensions, cone sizes and (voice coil) throw distances are all known quantities (there’s the EE in me...). I know, for instance, that in my dedicated theatre that’s a completely closed cube (18 x 14 x 9) there is about 2,270 cubic feet. My 18-inch Velodyne, with a high-excursion, 2-inch voice coil throw does a great job in there. So, if I were to calculate the area in square inches of an 18-inch circle, and multiply that by 2 (throw), I would come up with the volume of air (VA) the subwoofer moves in one cycle. Taking the ratio of that to 2,270 would give me a constant that could serve as a good starting point for any situation. Start with the room size, calculate backwards to VA, and then decide how many and/or how big the subs need to be. Obviously, through experience with different brands/models you would learn to sweeten (the formula) to taste, accounting for particularly strong or weak boxes. I guess I’ve done so many theatres that I can just look at a room and know what’s likely to work and what won’t. But now you’ve piqued my curiosity, and I intend to work through the math for the next couple of installations and see if I can’t refine the formula. If I go to that trouble, you can be sure it will be the focus of a column coming to your town soon.
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