The Subwoofer DIY Page v1.1
Choosing a Driver
last updated: 08 January 2009
When you're looking for the "perfect" driver for your DIY subwoofer system, be on the lookout for the following features:

    Low resonant frequency:
    Drivers with a lower resonant frequency ( Fs less than 40 Hz) will make better subwoofer drivers in most instances.

    Size Does Matter!
    The lower the frequency, the more air the driver's cone has to move. Consider this - for every octave that you go down in the audio spectrum, your speaker has to move 4 times as much to provide the same output level! As a consequence of this, your subwoofer is probably going to end up being the largest speaker in your living room. 

    The following can be used as a rough guide to determine the minimum size required for your subwoofer, based on the size of the woofers in your main speakers, and typical excursion specifications for subwoofer drivers.

    Mains

    Subwoofer
    Type, Driver size Typical Vd Target Vd Minimum Size
    2-way 11.5 cm (4.5") 40 160 20.3 cm (8")
    2-way 13.3 cm (5.25" 54 215 25.4 cm (10")
    MTM 11.5 cm (4.5") 80 319 25.4 cm (10")
    2-way 16.5 cm (6.5") 82 329 25.4 cm (10")
    MTM 13.3 cm (5.25") 107 429 30.5 cm (12")
    2-way 20.3 cm (8") 125 498 30.5 cm (12")
    3-way 25.4 cm (10") 259 1038 45.7 cm (18")

    Some popular subwoofer drivers are:

    Name Size Enclosure Type Cost
    NHT 1259 30.5 cm (12") Sealed $150
    Adire Audio Shiva 30.5 cm (12") Sealed, Vented $125
    Dayton Titanic 30.5 cm (12") Sealed $139
    Audio Concepts SV12 30.5 cm (12") Sealed $149

    Sturdy construction:
    Flimsy cones and driver baskets are likely to produce distortion, resulting in a less than perfect subwoofer design. To test the cone of a driver, push down one side of the cone near the surround. If the cone visibly distorts or doesn't move straight down into the basket, choose another driver.

    Impedance:
    If you're planning to build a passive subwoofer (i.e. one that's driven by your main amplifier), then its impedance has to be the same or greater than the amplifier's minimum impedance rating.  If you plan to build a powered subwoofer, then impedance is less of a concern (most subwoofer amplifiers can easily handle 4 ohm impedances).

    Please note that there is NO requirement for the impedance of your subwoofer to match the impedance of your main speakers.

    Car Audio Drivers:
    Typically, car audio drivers will not do well as drivers for a home subwoofer system, as they are usually designed to produce a good response when a car's cabin gain is taken into consideration.  However, there are a few for which  the T/S parameters suggest that they can produce good results in the home.  IOW, if you're planning to use a car audio driver in your design, treat it as a home audio driver and design a system based on its T/S parameters to get the best results.