ToolsElectronics, cables & data
Interconnection & impedance measurement
Level loss between an output and an input, and how to measure output and input impedances.
Voltage bridging: how much level is lost?
Ω
Ω
- Level loss
- -0.0864275dB
- Bridging ratio Zin / Zout
- 100: 1
Modern audio connects a low output impedance to a high input impedance (ratio of 10:1 or more), so almost no voltage is lost. Power matching (equal impedances) loses 6 dB.
Measure an output impedance
V
V
Ω
- Output impedance
- 111.111Ω
Measure an input impedance
V
V
Ω
- Input impedance
- 45555.6Ω
Measure with a sine tone in the middle of the audio band and a true-RMS meter. Choose a load or series resistor close to the expected impedance for the best accuracy.
How it works
Audio equipment uses voltage bridging: a low output impedance drives a much higher input impedance, so nearly the full voltage arrives. Measuring the voltage with and without a known resistor reveals an unknown impedance.
Formulas
- loss = 20 · log₁₀( Z_in / (Z_in + Z_out) )
- Z_out = R_L · (V₀ / V_L − 1)
- Z_in = R_s · V₂ / (V₁ − V₂)
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