Sub drivers for car audio typically have higher output, but also a higher resonant frequency. You'll typically find car audio enclosures tuned around 40Hz to maximize the output from 40Hz+, so the subs play louder. Below 40-ish Hz, the car's cabin itself acts as another sort of enclosure, supplying additional gain below the tuning of the box. You can see an illustration of this in the graphs provided in the
Infinity 1260w spec sheet. More simply, a car subwoofer can do more with less because there's less space to fill. Also, you're likely going to be sitting physically closer to a car sub than a home theater sub. Put a car sub into a 2000 cubic foot typical bedroom, however, and it'll probably struggle to fill that much space below its tuned frequency.
Room gain is less profound than automotive cabin gain, so the tuning of a home theater sub needs to be lower to achieve the same level of rumble. Indeed, there are valleys in the in-room low end response curve where the sub will have
no gain at all beyond its anechoic response (partially depending on placement, as corner loading a sub can provide boost you wouldn't achieve from floor and wall boundary loading). Once EQ is applied to flatten the room response, you'll appreciate having a stronger baseline target for your flattening.
This is why, in a home theater or hifi system, it's desirable to have a sub with an anechoic response reaching near or into infrasonics (below ~20Hz). The reason the Infinity in particular can migrate from the car into the home is because it has a relatively low resonant frequency of 23.5Hz. Notice that the Infinity spec sheet recommends a smaller box with a 32Hz port tune. That configuration wouldn't work in a home theater setting, as it's tuned to take advantage of a car's cabin gain. But a 3ft³ net volume (gross would be around 3 1/2 - 3 3/4, depending on wood thickness; displacement of bracing, vent, and driver; etc.) tuned to 23.5 Hz would work well in a home.
I'm still looking for a worthwhile design program that'll let me calculate box dimensions for a desired net volume and visualize how the bracing, slot vent, and so forth will all impact the gross volume.
The calculators on this page are pretty useful for figuring out the displacement of the bracing and ports, and for now I guess Google SketchUp would be the way to apply the numbers to a visual model. I haven't had much luck finding a program that'll do both, though.
Sonosub does this for tube-based subwoofers (well, lack of braces notwithstanding); but I'd still like to find a similar design program for box sub cabinets. (Edit:
Torres' Box Tuning Calculator looks promising.
Download w/o registering.)
Nevertheless, you can fudge the tuning a little and compensate with Polyfil if needed. Polyfil will make the sub behave as though it were in a bigger cabinet. And I don't think +- a cubic inch or two will cause a massive unexpected spike or dip in the response that would ruin the whole project. Tapped horns require more meticulous implementation, but I think simple vented subs are more tolerant of imperfection in dimensions. Hopefully
@TLS Guy can correct me if I'm wrong.
And yes, if you DIY your sub, you will end up with something that outperforms more expensive subs for less money. If you can DIY, you should. Don't get frustrated and give up!
Playing with WinISD, the HTS web-based calculators, and Torres' Calculator, I came up with this. Build a box out of 3/4" MDF, outer dimensions 19.5"H x 17"W x 24"D (including a double front baffle so you can countersink the driver), build in a 1"H x 15.5"W x 20.75"D slot (no bend needed, using the inner-cabinet bottom and sides as 3 of its walls), and add a brace in the middle (18"H x 15.5"W, 12" hole centered behind the driver). That'll give you net 3.02ft³ internal volume with a vent tuned to 23.83Hz, having a port velocity of ~18m/s at 125W. Dropping in the Infinity 1260w should result in an F3 of 22.5Hz, output of 105dB at 20Hz at 300W at 1m, ~111dB from 29Hz+, and more satisfaction than anyone has a right to expect from a $70 driver.
Then build a second one, for great justice, and because that Crown amp will easily drive two of those subs. Then get a miniDSP + UMIK-1 to manage them.
Or if you prefer, the
Dayton Titanic 15" in a 6ft³ box tuned to 16.8Hz would handle 600W of power, at which point it's about 3dB louder than the Infinity at 30Hz; would have an F3 of 19Hz, and would play down to 14.5Hz (at 107dB with 600W of power) without bottoming out. This would result in a box 24.25"H x 22"W x 28"D with a 2"H x 9"W x 52.75"L vent with a bend or two (I think -- WinISD and Torres seem to disagree about this, with WinISD claiming a length of 25". I can find another calculator to confirm one or the other if you want to pursue this option).
