Beginner
CT Sounds
CT Sounds Tropo 12 D4
$129.99A dual 4 ohm 12 that wires to 8 or 2 ohms with one driver, which keeps the amplifier choice open.
Check price on AmazonPower calculator
Car Audio SPL Estimate Calculator
Quick answer
SPL is sensitivity plus ten times the log of the power. An 85 dB subwoofer on 500 watts produces about 112 dB at one metre anechoic, and a sealed car interior typically adds another 6 to 12 dB below its transition frequency.
Result
Estimated SPL in cabin 118 dB Convention
Anechoic at 1 metre 112 dB Published figure
Gain from power 27 dB Published figure
Gain from driver count 0 dB Published figure
Sustained exposure above roughly 100 dB causes permanent hearing damage in minutes, and the damage does not heal. A system that reaches these numbers is not one to sit inside at full output.
The formula
SPL = sensitivity + 10 x log10(watts) + 10 x log10(driver count)
This is an estimate of anechoic output, plus a cabin allowance that is a convention. It is NOT a competition score. A metered burp on a calibrated meter at the windscreen measures peak pressure at one point in a sealed vehicle and routinely reads far higher than this. Treat the number as a comparison between options rather than as a prediction.
The figures above are computed with these exact inputs: Driver sensitivity 85 dB at 1W/1m, Power per driver 500 W RMS, Number of drivers 1, Cabin gain 6 dB.
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 |
|---|---|---|
| SPL = sensitivity + 10 x log10(power) | Published figure | SPL = sensitivity + 10 x log10(power), the logarithmic power relation |
| Cabin Gain: 6 | Convention | Cabin gain: the low frequency reinforcement a sealed vehicle interior provides below its pressure-vessel transition. Figures between 6 and 12 dB are quoted. It varies enormously with vehicle size, sealing and frequency and is not a published specification |
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
ORION
Orion Cobalt CBW124D
$74.95The cheapest dual 4 ohm 12 in this catalog from a brand that has published specifications.
Check price on Amazon Intermediate
Skar Audio
Skar Audio SDR-12 D4
Price varies, check the listingA 2.5 inch four layer coil and a published 22 Hz to 300 Hz response, which is the usual first real subwoofer.
Check price on Amazon Intermediate
Skar Audio
Skar Audio SVR-12 D4
Price varies, check the listingA step up in motor and excursion from the SDR at the same coil configuration, so an existing box often still suits it.
Check price on Amazon Expert
Skar Audio
Skar Audio EVL-12 D4
Price varies, check the listingHigh excursion and a heavy motor, which means it wants a larger, properly braced box and real power behind it.
Check price on Amazon Expert
Skar Audio
Skar Audio VXF-12 D4
Price varies, check the listingA competition driver. Do not buy it unless the electrical system and the enclosure are already built for it.
Check price on AmazonFrequently asked questions
- How does the spl estimate calculation work?
- SPL = sensitivity + 10 x log10(watts) + 10 x log10(driver count). This is an estimate of anechoic output, plus a cabin allowance that is a convention. It is NOT a competition score. A metered burp on a calibrated meter at the windscreen measures peak pressure at one point in a sealed vehicle and routinely reads far higher than this. Treat the number as a comparison between options rather than as a prediction.
- 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.