FORMULAS & Electrical Units
Used in Speaker Circuits

Inductance

The unite of inductance in the henry.
All smaller units should be converted to henrys before using the formulas.
1 millihenry (mH) = 0.001H  or 1 x 10-3H
1 microhenry (mH) = 0.000001H or 1 x 10-6H

Capacitance

The unit of capacitance is the farad.
All smaller units should be converted to farads before using the formulas.
1 microfarad (mf) = 0.000001 farad or 1 x 10-6
1 picofarad (pf) = 0.000000000001 farad or 10 x 10-12farad
 

OHM'S LAW FOR SPEAKERS

For alternating current, the Ohms's Law formulas are:
E = I Z
I = E / Z
Z = E / I
E is the voltage in volts,
I is the current in amperes and
Z is the impedance in ohms
 

REACTANCE & RESONANCE

Capacitors

Capacitive reactance:
Xc = 1 / (2pƒC)
 
To get the value of a capacitor that will give a specified reactance at a given frequency:
C = 1 / (2pƒXc)

Inductance

Inductive reactance:
XL = 2pƒL
To get the value of a choke that will give a specified reactance at a given frequency:
L = XL / (2pƒ)

Resonance

ƒ = 1 / [2psqrt(LC)]

Parallel Resistors

Where R1 = R2 = R3, and N is the number of resistors.
Total (Rt) = R / N
 
For mixed value resistors:
Rt = 1 / [ (1/R1) + (1/R2) + (1/R3) + . . . ]
 
If N = 2
Rt = (R1 *  R2) / (R1 + R2)

Series Resistors

Rt = [R1 + R2 + R3 + . . . ]

Parallel Capacitors

Ct = [C1 + C2 + C3 + . . . ]

Series Capacitors

Where C1 = C2 = C3, and N is the number of capacitors.
Total (Ct) = C / N
 
For mixed value capacitors:
Ct = 1 / [ (1/C1) + (1/C2) + (1/C3) + . . . ]
 
If N = 2
Ct = (C1 *  C2) / (C1 + C2)

Parallel Inductors (Chokes)

Where L1 = L2 = L3, and N is the number of inductors.
Total (Lt) = L / N
 
For mixed value inductors:
Ct = 1 / [ (1/C1) + (1/C2) + (1/C3) + . . . ]
 
If N = 2
LCt = (L1 *  L2) / (L1 + L2)

Series Inductors (Chokes)

Lt = [L1 + L2 + L3 + . . . ]

Resistor & Capacitor in Series

Z = sqrt ( R2 + XC2 )

Resistor & Capacitor in Parallel

Z = [R * X1] / [sqrt ( R2 + XL2 )]

Resistor, Inductor, & Capacitor in Parallel

Z = [R * XL * XC] / sqrt[(XL2XC2) + (R2(XL - XC)2]
 

CONVERSION FACTORS FOR SPEAKER COMPLIANCE

Speaker compliance is sometimes measured in cm/dyne- the CGS (centimeter-gram-second) system because the centimeter is a convenient unit to use in measuring cone diameter.   Sometimes compliance is shown in mixed units of mm/Newton or even as its reciprocal term-stiffness-in Newton/Meter, the MKS (meter-kilogram-second) system.

To change cm/dyne to mm/Newton:

1cm = 10mm
1 * 105dynes = 1 Newton
Cms (cm/dynes) * 106 = Cms (mm/Newton)

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