Complete Build Example: 12-Inch Sealed Subwoofer for a Daily Driver

This walkthrough shows a realistic sealed-subwoofer build for a daily-driven sedan where music quality matters more than extreme output. The goal is controlled bass, reasonable cost, and a box that actually fits the car.

The Requirements

Vehicle: Honda Accord sedan with trunk space available
Budget: about $400 total for the driver, materials, and install supplies
Music use: rock, jazz, and acoustic with accurate bass instead of boom
Amplifier on hand: 500 W RMS
Packaging limit: 1.5 ft^3 net internal volume

Step 1: Driver Selection

A sealed daily-driver build usually wants a driver with a workable Qts, enough power handling for the amplifier, and displacement that still fits the available box size.

Example driver: Dayton Audio RSS315HF-4

The numbers below show how a sealed-box workflow fits a real 12-inch daily-driver build. Confirm the latest published specs before ordering parts.

Fs: 28 Hz
Qts: 0.51
Vas: 3.54 ft^3 (100 L)
Xmax: 18 mm
Sensitivity: 87.3 dB
Power handling: 600 W RMS
Street price: about $140

Step 2: Box Volume Math

If we chase a textbook Butterworth target first:

Vb = Vas / [ (Qtc / Qts)^2 - 1 ]
Vb = 3.54 / [ (0.707 / 0.51)^2 - 1 ]
Vb = 3.85 ft^3

That is too large for the available space, so we check the response with the real packaging limit of 1.5 ft^3 net:

Qtc = Qts x sqrt(Vas / Vb + 1)
Qtc = 0.51 x sqrt(3.54 / 1.5 + 1)
Qtc = 0.93

Qtc of 0.93 is a slightly peaked sealed alignment. It gives a little extra output around system resonance, which is a fair trade in a box this size.

Fc = Fs x (Qtc / Qts)
Fc = 28 x (0.93 / 0.51)
Fc = 51 Hz

F3 = Fc x 0.815
F3 = 41.5 Hz

This is not a flat Butterworth box. System resonance is around 51 Hz, and the electrical -3 dB point lands in the low-40 Hz range before cabin gain. In a typical sedan that still works well for music.

Step 3: Exterior Dimensions

Net volume needed is 1.5 ft^3, or 2,592 cubic inches. Add about 0.15 ft^3 for driver displacement and about 0.10 ft^3 for bracing, and the gross target becomes about 1.75 ft^3.

A compact internal layout for that target:

Width: 14 in
Height: 14 in
Depth: 15.4 in internal

With 3/4-inch material on all sides, the outside size comes out to about 15.5 in wide by 15.5 in tall by 16.9 in deep.

Step 4: Materials and Budget

Item	Qty	Cost
3/4-inch MDF sheet	1	$45
Construction adhesive	1 tube	$8
Wood screws	1 box	$6
Terminal cup	1	$8
12 AWG speaker wire	10 ft	$5
Carpet or wrap	3 yd	$25
Spray adhesive	1 can	$12
Polyfill	1 bag	$10
Weatherstrip foam tape	1 roll	$6

That keeps the enclosure materials near $125, leaving room in the budget for the driver and install supplies.

Step 5: Cut List

Top and bottom: 15.5 in x 16.9 in (2)
Left and right sides: 14 in x 15.5 in (2)
Front baffle: 15.5 in x 15.5 in (1)
Back panel: 15.5 in x 15.5 in (1)
Cross braces: 2 in x 13 in (3)

Step 6: Assembly Sequence

Cut all panels and the driver opening, then dry-fit everything square.
Glue and screw the shell together with pilot holes on every joint.
Seal the interior seams, add braces, and install the terminal cup.
Sand, wrap, and finish the exterior.
Add polyfill, gasket the driver opening, wire the driver, and perform a leak check.

Step 7: Amplifier Settings

Subsonic filter: 25 Hz, 24 dB per octave
Low-pass filter: 80 Hz, 24 dB per octave as a starting point
Gain target: about 44.7 V for 500 W into 4 ohms
Bass boost: 0 dB to start

Expected Result

With about 500 W available, this build should land in the 108 to 112 dB range near 50 Hz in a typical car, with musical extension in the low-40 Hz range before cabin gain helps below that point. The character should be warm, controlled, and easy to live with every day.