The Subwoofer DIY Page v1.1
How low should a subwoofer go?
last updated: 09 August 2015
For all subwoofer designs, there are considerable tradeoffs in cutoff frequency, enclosure size and power handling. Generally, the lower the cutoff frequency, the larger the enclosure and the lower the power handling of the system. Consider the following when deciding on your subwoofer requirements:

Size Limitations:
Do you want something small and unobtrusive or is something the size of a small refrigerator Ok? Smaller subwoofers tend to have higher cutoff frequencies, but the SAF is higher as well.  Subwoofer drivers typically require big boxes to perform at their best.  You can use the following as a rough guide for determining how much living room space you'll be giving up to your subwoofer, using typical driver sizes:
Box Size
Size Internal External
20.3 cm (8") 28 l - 50 l (1.0 - 1.8 cu.ft.) 40 l - 67 l (1.4 - 2.4 cu.ft.)
25.4 cm (10") 50 l - 71 l (1.8 - 2.5 cu.ft.) 67 l - 92 l (2.4 - 3.3 cu.ft.)
30.5 cm (12") 57 l - 113 l (2.0 - 4.0 cu.ft.) 75 l - 142 l (2.7 - 5.0 cu.ft.)

Design Goals:
Is the subwoofer going to be used as part of a small three-piece system that will be used mostly for popular music, or is it going to be part of a large home theater system? For the former example, a subwoofer that reaches below 45 Hz should be good enough, while the latter may require a subwoofer that extends below 30 Hz.

Room Gain:
In most rooms, the room itself provides additional gain at frequencies below approximately 30 Hz. There's a slight risk of creating a boomy system if you create a design that on paper has a cutoff point much below 30 Hz.

Car Audio:
Most cars provide an additional gain of approximately 12dB/octave below 80 Hz or so. Note that sealed and 4th order bandpass systems have response characteristics that naturally complement the natural bass boost provided by a car's interior. When designing a sealed subwoofer for car audio use, aim for a cutoff point between 40 - 50 Hz to achieve the best results.  For other types of systems, you will need to adjust the design parameters a bit to get the best results in-car.