Beginner
Goldwood Sound, Inc.
Goldwood TR12S sealed 12
$48.99The cheapest sealed 12 here, and sealed is the alignment that forgives a volume error.
Check price on AmazonEnclosure calculator
Sealed Subwoofer Box Volume Calculator
Quick answer
Sealed box volume is Vas divided by ((Qtc/Qts) squared minus 1). A driver with Vas of 1.2 cubic feet and Qts of 0.42 needs about 1.09 cubic feet for a Qtc of 0.707, and the system resonance lands near 55 Hz.
Result
Net internal volume 0.654 cu ft Published figure
In cubic inches 1131 cu in
System resonance Fc 53.9 Hz Published figure
Total system Q 0.707 Qtc
This is NET volume, which is the air the driver sees. Add back the driver displacement and any bracing to get the internal volume you actually build.
The formula
Vb = Vas / ((Qtc / Qts)^2 - 1), and Fc = Fs x (Qtc / Qts)
Vas, Qts and Fs are published on the driver specification sheet. Qtc is the alignment you choose: 0.707 is maximally flat, below 0.6 is over-damped and sounds lean in a car, and above 0.8 is peaky. If your driver does not publish Vas and Qts, this calculation cannot be done and no table of box sizes by driver diameter is a substitute.
The figures above are computed with these exact inputs: Vas 1.2 cu ft, Qts 0.42, Fs 32 Hz, Target Qtc 0.707.
What this calculator assumes
Some of these are published physics or manufacturer figures and some are conventions. They are not the same kind of number, so each one is labeled.
| Assumption | Kind | Where it comes from |
|---|---|---|
| Sealed-box alignment from Thiele/Small parameters | Published figure | Sealed-box alignment from Thiele/Small parameters: Vb = Vas / ((Qtc/Qts)^2 - 1) |
Gear that matches this result
Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.
Beginner
Q Power
QPower HD112 sealed 12
$49.99A heavy duty single 12 sealed box built for a driver that is going to get used hard.
Check price on Amazon Intermediate
Rockville
Rockville RMS12, 1.6 cu ft
$54.95A stated 1.6 cubic feet in 3/4 inch MDF, which is at the large end of sealed for a 12 and suits a low Qts driver.
Check price on Amazon Intermediate
BELVA
Belva MDFS12, 1.0 cu ft
$69.99A stated 1.0 cubic feet, which is the most common published sealed recommendation for a 12 inch driver.
Check price on Amazon Expert
Atrend
Atrend Bbox single sealed 12
$72.05Better finish and bracing than the budget boxes, with terminals that will take real wire.
Check price on AmazonFrequently asked questions
- How does the sealed box volume calculation work?
- Vb = Vas / ((Qtc / Qts)^2 - 1), and Fc = Fs x (Qtc / Qts). Vas, Qts and Fs are published on the driver specification sheet. Qtc is the alignment you choose: 0.707 is maximally flat, below 0.6 is over-damped and sounds lean in a car, and above 0.8 is peaky. If your driver does not publish Vas and Qts, this calculation cannot be done and no table of box sizes by driver diameter is a substitute.
- Are these figures published or are they rules of thumb?
- Both, and the page labels which is which. The Helmholtz port relation, the Thiele/Small alignment equations, cone area geometry, Ohm’s law, conductor resistance and ampacity, and manufacturer specifications are published and are labeled as such. Amplifier efficiency, cabin gain, the farad per thousand watts rule, port area per cubic foot and coverage percentages are conventions with no measurement behind them, and they are labeled as conventions.
- Why does this calculator sometimes refuse to give an answer?
- Because there genuinely is not one. A port can be too large in area for the box and tuning asked of it, a vented alignment stops describing a useful box outside a Qts range, and a sealed box cannot produce a total Q below the driver’s own. In each case the calculator returns nothing and explains why, rather than extrapolating past the end of a published relation.
- Do I still need an installer if I use this?
- Many owners do their own 12V work, and these are the figures that work is sized from. What matters is that a car battery delivers hundreds of amps into a short without hesitating, so the main fuse goes within 18 inches of the battery positive terminal and the battery comes off before power wire goes in. If any of that is beyond what you want to take on, a professional installer is money well spent.
Researched guidance, not professional advice. These results are planning figures from published relations and manufacturer specifications. Fit the main fuse within 18 inches of the battery positive terminal, because that fuse protects the wire and the wire is what starts a fire. Disconnect the battery before running power wire, use a grommet through every piece of sheet metal, and remember that sustained high sound pressure causes permanent hearing damage.