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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