Methodology

About CarAudioCalc

CarAudioCalc exists to answer the arithmetic questions in car audio with the working shown. 16 calculators and 256 generated answer pages, all computed from the same library at build time, with 252 products verified against the Amazon catalog.

We separate published figures from convention

Two very different kinds of number get quoted interchangeably in car audio advice, and conflating them is how bad guidance spreads. Every figure on this site carries one of two labels.

Published means physics, geometry, or a figure published by a manufacturer or standards body. The Helmholtz resonator port length relation. The Thiele and Small sealed and vented alignment equations. Cone area geometry. Ohm's law. NEC Chapter 9 Table 8 conductor resistance and NEC Table 310.16 ampacity. The CTA-2006 amplifier power measurement standard. A driver's own Vas, Qts, Fs and Xmax.

Convention means a widely repeated rule of thumb with no measurement behind it. One farad of capacitance per thousand watts. Twelve to sixteen square inches of port per cubic foot. Eighty percent class D amplifier efficiency. Six to twelve decibels of cabin gain. Twenty five percent sound deadening coverage. Setting the gain by ear. These are planning numbers at best, and the first one is close to meaningless.

We return nothing rather than inventing a figure

Every calculation here returns no answer when the inputs fall outside what the published relations cover, and explains why. 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 range of Qts. A sealed box cannot produce a total system Q below the driver's own.

The version of this that matters most: if a manufacturer does not publish a recommended enclosure volume for a driver, we say so rather than estimating one. A wrong box volume ruins a subwoofer, and a figure borrowed from a different driver of the same nominal size is not a substitute for the real one. Drivers of the same diameter routinely want volumes that differ by a factor of two, because enclosure volume follows compliance rather than size.

We do not test products in person

Every product recommendation here is researched from published specifications, owner manuals, and the consensus of verified owner reviews. We have not installed these products, measured them, or listened to them, and we never claim to have. Any site that claims hands-on testing of forty subwoofers is telling you a story.

What we do instead is read every returned product title against what the page actually claims. Car audio is a difficult category for this: a search for a subwoofer returns loaded enclosures and powered under-seat boxes, a search for a car audio battery returns cranking batteries rated in cold cranking amps, and capacitors are sold as ten and eighteen farads at prices where that capacitance is not physically plausible. Every rejected product is recorded in the repository with the reason it was cut.

Safety is real advice, not boilerplate

A car battery will deliver several hundred amps into a short without any drama at all. The main fuse goes within 18 inches of the battery positive terminal, because every inch of cable before it is unprotected. That fuse protects the wire and not the equipment. 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 that does not heal.

Corrections

If a figure here is wrong, we would rather know. Get in touch and tell us which number and what the published source says, and it will be fixed.