Units and calculations

Units :

Names come from these of scientists : Volta,Ampère,Watt,Ohm,Faraday...

U = Voltage Unit: Volt V Multipliers : Kilo (x1.000): K Méga (x1.000.000): M

I = Current Unit: Ampère A Dividers : Mili (/1.000): m Micro (/1.000.000): µ Nano Pico

P = Power Unit: Watt W

R = Résistance Unit: Ohm Ω The BEL is the logarithmic acoustic unit , we use the decibel : dB.

C = Capacity Unit: Farad F Ex : + 6dB = voltage x 2 and power x 4  - 20dB = voltage / 10 et power / 100

F = Fréquency Unit: Hertz Hz

Z = Impedance Unit: Ohm Ω ( The impedance is the equivalent of the resistance but in alternative current . )

Examples: a capacity of 47µF and 25V, a resistor of 22KΩ and 1 / 4W , the line voltage 220V~ and 16A , a loud speaker with an impedance of 8Ω and 30W.

The line voltage frequency in France is 50Hz .

What counts for an amplifier is the continuous efficient power ( RMS ) . Improper terms  : musical power, admissible, maximum , PMPO .

Calculation : two formulas ( we can calculate the two others )

U= R x I Voltage (Volts) = Résistance (Ohms) x Current (Ampères) P= U x I Power (Watts) = Voltage (Volts) x Current (Ampères)

P= U² / R (P= U x U / R) Power(Watts) = Voltage² (Volts) / Résistance (Ohms)

P= R x I² (P= R x I x I) Power(Watts) = Résistance (Ohms)x Current² (Ampères) Rappel : I= U / R R= U / I U= P / I I= P / U

Examples : A résistor of 1000Ω and 12v A radiator of 1000w and 220v A loud speaker of 8Ω and 30w

U= R x I then I = U / R I = 12/1000 I = 0.012A equal 12mA P= U x I then I = P / U I = 1000/220 I = 4,545 A P=U² / Z then U²= P x Z U= √P x Z U= √30x8 U= 15.491V

P= U x I then P= 12x0.012 P= 0.144W equal 144mW U= R x I then R= U / I R= 220/4,545 R= 48,4 Ω U= Z x I then I = U /Z I = 15.491/8 I = 1.936A