Chris
posted this
03 August 2021

- Last edited 03 August 2021
Fantastic work CD!

Impedance, the rated 2, 4, amd 8 Ohms Load on your Amp, is typically the Coils Inductive Reactance: **X**_{L} = 2π f L

2 Ohms is not the DC Resistance, this part is somewhat confusing. Measuring a Speaker will give you a closer approximation.

I observing the typical Speaker Drive Coil, we see it is fairly small with few turns:

It is the Inductance we see, that is important, as the inductance changes when the Speaker Drive Coil is inserted, we see the Load on the Amp change.

### Example:

- Voltage = 10 Volts RMS
- Frequency = 25 Hertz
- Inductance = 0.5 Henries

X_{L} = 2 π f L = 6.28 x 25Hz x 0.5H = 78.5 Ohms

Current I = Voltage V / Resistance R = 10 Volts / 78.5Ohms = 0.1273 Amps.

Watts = V I cos( θ ) = 10 x 0.1273 x 1 = 1.2738 Watts.

I hope this helps My Friend, oh yes, there is an impedance calculator in the Aboveunity Member Calculator.

Best Wishes,

Chris