|The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R.
Ohm's law equation (formula): V = I × R and the power law equation (formula): P = I × V.
P = power, I or J = Latin: influare, international ampere, or intensity and R = resistance.
V = voltage, electric potential difference Δ V or E = electro motive force (EMF = voltage).
|Enter any two known values and press "calculate" to solve for the two others. Please, enter only two values.|
|V comes from "voltage" and E from "electromotive force". E means also energy, so V is chosen. Energy = voltage × charge. E = V × Q. Some like better to stick to E instead to V, so do it.|
|Voltage V = I × R = P / I = √(P × R) in volts V Current I = V / R = P / V = √(P / R) in amperes A
Resistance R = V / I = P / I2 = V2 / P in ohms Ω Power P = V × I = R × I2 = V2 / R in watts W
| The Big Power Formulas
Electrical and mechanical power calculation
In sound engineering there is no Impedance matching or Power matching.
In audio we use only high Impedance bridging or Voltage bridging.
Power is like all energy sizes
primarily a calculated value.
Tip: The electric power triangle (power formula)
Please enter two values, the third value will be calculated.
The magic triangle can be used to calculate all formulas of the "electric power law". You hide with
a finger the value to be calculated. The other two values show then how to do the calculation.
Calculations: Ohm's law - Ohm's magic triangle
Measurement of input impedance and output impedance
ALTERNATING CURRENT (AC) ~
Vl = line voltage (volts), Vp = phase voltage (volts), Il = line current (amps), Ip = phase current (amps)
Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)
|Current (single phase): I = P / Vp×cos φ||Current (3 phases): I = P / √3 Vl×cos φ or I = P / 3 Vp×cos φ|
|Power (single phase): P = Vp×Ip×cos φ||Power (3 phases): P = √3 Vl×Il×cos φ or P = √3 Vp×Ip×cos φ|
|frequency f||hertz (Hz)||1/s|
|force F||newton (N)||kg·m/s²|
|pressure p||pascal (Pa) = N/m²||kg/m·s²|
|energy E||work joule (J) = N·m||kg·m²/s²|
|power P||watt (W) = J/s||kg·m²/s³|
|electric charge Q||coulomb (C) = A·s||A·s|
|voltage V||volt (V)= W/A||kg·m²/A·s³|
|capacitance C||farad (F)= C/V = A·s/V = s/Ω||A²·s4/kg·m²|
|inductance L||henry (H) = Wb/A = V·s/A||kg·m²/A²·s²|
|resistance R||ohm (Ω) = V/A||kg·m²A²·s³|
|conductance G||siemens (S) = A/V||A²·s³/kg·m²|
|magnetic flux Φ||weber (Wb) = V·s||kg·m²/A·s²|
|flux density B||tesla (T) = Wb/m² = V·s/m²||kg/A·s²|
|The flow of electric charge Q is referred to as an electric current I. The amount of charge per unit time
is the change in electric current. A current flows at a constant value I. during the time t, it transports the
charge Q = I × t. For a temporally constant power, the relationship between the charge and current:
I = Q / t or Q = I × t. Through this relationship, the basic units of amps and second the Coulomb in International System of Units is set. The Coulomb unit can be represented as 1 C = 1 A × s.
In acoustics we have an "Acoustic equivalent for ohm's law"
Relationships of acoustic sizes associated with plane progressive sound waves
Conversions of many units, like power and energy
prefixes | length | area | volume | weight | pressure | temperature | time | energy | power | density | velocity | acceleration | force
[top of page]