I posed this question, because I'm looking for a simple answer as to why this resistor is needed In series with the speaker when measuring impedance.
My thought would have been that you use your amplifier to send a signal to the speaker, staggering the frequency sweep to one or two seconds at each. frequency and measuring the voltages at each frequency across the speaker. Have an ammeter In series with a speaker. To measure amps. One can then plot a graph of the impedance response.
Please keep in mind that my knowledge is at beginner level, and if you could, think of the simplest individual when constructing your answer. I understand equal. V=IR., but not a whole lot more.
My thought would have been that you use your amplifier to send a signal to the speaker, staggering the frequency sweep to one or two seconds at each. frequency and measuring the voltages at each frequency across the speaker. Have an ammeter In series with a speaker. To measure amps. One can then plot a graph of the impedance response.
Please keep in mind that my knowledge is at beginner level, and if you could, think of the simplest individual when constructing your answer. I understand equal. V=IR., but not a whole lot more.
But one good way to measure current is to measure voltage (across a resistor). Magnetic current sensors can be quite noisy by comparison, but they will also serve, but a resistor is simple and cheap.
Bigger is better until the measured signal drops too far.
The amplifier would ensure the voltage is the same for each frequency.
- I use an Audio Precision Analyzer for this type of impedance measurement, however other equipment can be used. The AP is an instrument that gives you a nice GARPH/PLOT.
- Sweep the amplifier output for flatness.
- Add a series resistor 10x of the speaker. This is then a current source.
- Plot the voltage across the speaker.
- Replace the speaker with a 4 Ohm resistor and plot the voltage.
- Replace the 4 Ohm with an 8 Ohm resistor and plot the voltage.
- The graph now has a 4 & 8 Ohm reference.