16 calculators
Car Audio Calculators
Every calculator here shows its formula, renders a worked example into the page itself so it can be read without scripts, and returns nothing rather than a guess when the inputs fall outside the published relations. Figures are labeled as published or as convention, because they are not the same kind of number.
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Enclosure
- Sealed box volume Vb = Vas / ((Qtc / Qts)^2 - 1), and Fc = Fs x (Qtc / Qts) Work out the sealed enclosure volume a subwoofer needs from its published Thiele/Small parameters, with the resulting sy
- Ported box volume Vb = 20 x Vas x Qts^3.3, Fb = 0.42 x Fs x Qts^-0.96, F3 = 0.26 x Fs x Qts^-1.4 Free subwoofer box calculator: enter your sub's Vas, Qts and Fs to get the ported box volume in cubic feet, the tuning f
- Port length Lv = (1.463e7 x R^2) / (Fb^2 x Vb) - (k x R) Calculate the length of a round subwoofer port from the box volume, the tuning frequency and the port diameter, using th
- Slot port Equivalent diameter = 2 x sqrt(area / pi), then Lv = (1.463e7 x R^2) / (Fb^2 x Vb) - (k x R) Size a rectangular slot port for a subwoofer enclosure: length from the Helmholtz relation, area against the per cubic f
- Box dimensions Internal volume = (W - 2t) x (H - 2t) x (D - 2t), divided by 1,728 for cubic feet Convert external subwoofer box dimensions and panel thickness into internal volume in cubic feet and cubic inches, which
- Net vs gross volume Net = gross internal volume - driver displacement - port displacement - bracing Subtract driver displacement, port displacement and bracing from a subwoofer box gross volume to get the net internal vo
Wiring
Electrical
- Fuse size I = P_rms / (efficiency x volts), then fuse at or below the conductor ampacity What size fuse for a 1000 watt amp? About 100 A on 2 gauge or 1/0 wire. Enter RMS watts and wire size to get the amp dra
- Wire gauge Vdrop = 2 x run length x amps x (ohms per 1000 ft / 1000) Find the smallest power wire that carries an amplifier current draw over a given run while holding voltage drop within t
- Big 3 wire size Size each of the three runs for the alternator rated output at the target voltage drop Size the three cables of a big 3 upgrade against your alternator output: alternator positive to battery positive, batter
- Capacitor size Energy E = 0.5 x C x V^2, and capacitance for a given sag C = I x t / dV Compare what the one farad per thousand watts rule of thumb recommends against what the physics of a capacitor actually
- Alternator output Alternator amps = (audio RMS watts / (efficiency x volts)) + accessory load, times headroom How many amp alternator do you need? A 1,000 W system needs about 171 A, 2,000 W about 275 A. Add amp draw to the vehicl
Power
- RMS vs peak power dB difference = 10 x log10(P2 / P1) Convert between the peak or max power figure printed on a car audio box and the RMS rating that actually matters, and se
- SPL estimate SPL = sensitivity + 10 x log10(watts) + 10 x log10(driver count) Estimate sound pressure level from driver sensitivity, amplifier power and driver count, with cabin gain shown separatel
