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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^{3}H
 1 microhenry (mH) = 0.000001H or 1 x 10^{6}H
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^{12}farad

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:
 X_{c} = 1 / (2pƒC)

 To get the value of a capacitor that will give a specified
reactance at a given frequency:
 C = 1 / (2pƒX_{c})
Inductance
 Inductive reactance:
 X_{L} = 2pƒL
 To get the value of a choke that will give a specified
reactance at a given frequency:
 L = X_{L} / (2pƒ)
Resonance
 ƒ = 1 / [2psqrt(LC)]
Parallel Resistors
 Where R_{1} = R_{2} = R_{3}, and N
is the number of resistors.
 Total (R_{t}) = R / N

 For mixed value resistors:
 R_{t} = 1 / [ (1/R_{1}) + (1/R_{2})
+ (1/R_{3}) + . . . ]

 If N = 2
 Rt = (R_{1} * R_{2}) / (R_{1}
+ R_{2})
Series Resistors
 R_{t} = [R_{1} + R_{2} + R_{3}
+ . . . ]
Parallel Capacitors
 C_{t} = [C_{1} + C_{2} + C_{3}
+ . . . ]
Series Capacitors
 Where C_{1} = C_{2} = C_{3}, and N
is the number of capacitors.
 Total (C_{t}) = C / N

 For mixed value capacitors:
 C_{t} = 1 / [ (1/C_{1}) + (1/C_{2})
+ (1/C_{3}) + . . . ]

 If N = 2
 Ct = (C_{1} * C_{2}) / (C_{1}
+ C_{2})
Parallel Inductors (Chokes)
 Where L_{1} = L_{2} = L_{3}, and N
is the number of inductors.
 Total (L_{t}) = L / N

 For mixed value inductors:
 C_{t} = 1 / [ (1/C_{1}) + (1/C_{2})
+ (1/C_{3}) + . . . ]

 If N = 2
 LCt = (L_{1} * L_{2}) / (L_{1}
+ L_{2})
Series Inductors (Chokes)
 L_{t} = [L_{1} + L_{2} + L_{3}
+ . . . ]
Resistor & Capacitor in Series
 Z = sqrt ( R^{2} + X_{C}^{2} )
Resistor & Capacitor in Parallel
 Z = [R * X_{1}] / [sqrt ( R^{2} + X_{L}^{2}
)]
Resistor, Inductor, & Capacitor in Parallel
 Z = [R * X_{L} * X_{C}] / sqrt[(X_{L}^{2}X_{C}^{2})
+ (R^{2}(X_{L}  X_{C})^{2}]

CONVERSION FACTORS FOR SPEAKER COMPLIANCE
 Speaker compliance is sometimes measured in cm/dyne the
CGS (centimetergramsecond) 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 termstiffnessin Newton/Meter, the MKS (meterkilogramsecond)
system.
To change cm/dyne to mm/Newton:
 1cm = 10mm
 1 * 10^{5}dynes = 1 Newton
 C_{ms} (cm/dynes) * 10^{6} = C_{ms}
(mm/Newton)

