Calculate voltage, current, resistance, or power using Ohm's Law. Select what you want to find, then enter any two known values.
A 3000W RMS amplifier at 80% efficiency running at 14.4V:
• Actual power draw = 3000W ÷ 0.80 = 3750W
• Current draw (I) = P ÷ V = 3750W ÷ 14.4V = 260.4A
Testing a subwoofer with a multimeter: 1V applied, 0.25A measured:
• Resistance (R) = V ÷ I = 1V ÷ 0.25A = 4Ω
• This is a 4-ohm voice coil
Measuring 40V AC across a 2Ω subwoofer load:
• Power (P) = V² ÷ R = 40² ÷ 2 = 1600 ÷ 2 = 800W RMS
Speakers are reactive loads — their impedance changes with frequency due to inductance (Le), back-EMF, and enclosure tuning. The nominal impedance you enter here is a baseline reference. At resonance, impedance can spike 5-10× above nominal. At the enclosure tuning frequency, "box rise" typically doubles the effective load. Use these calculations as a starting point, then verify with measured impedance data for precision applications.