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You will need anaudio sine-wave generator, frequency counter, ac voltmeter, 1000 ohm resister, a 10 ohm 1% precision resistor, and the driver to test.
The test setup formeasuring driver impedance is shown here. Connect everything as shown.
First, calibrate byinserting the 10 ohm resistor in place of the driver.
Adjust the voltageoutput of the audio frequency sine-wave generator until the ac voltmeter reads 0.01 volts.
Replace the 10 ohmresistor with the driver to be tested.
Keep the outputvoltage constant. 0.01 volts represents 10 ohms, 0.015 volts represents 15ohms, etc.
Vary the frequencycontrol of the audio frequency generator to find maximum resistance ( Rmax ). Atthat point, frequency is resonant frequency ( Fs ).
Adjustfrequency to 1 Hz to find ( Re ).
resistance ( R x ) =ohms.
Adjust the sine-wavegenerator until the resistance is equal to Rx. This will occur twice as shown in thegraph above. F1 is the lower frequency when the resistance equals Rx. F2 isthe higher frequency when the resistance equals Rx.
With the speaker facingupward place small weights or U. S. nickels evenly around the dust cap in thecenter. 6 U. S. nickels equals 30 grams. With the mass on the speakerfind the shifted resonant frequency.
To find the voice coilinductance of the driver, set the frequency of the sine-wave generator at 1000 Hz andmeasure the resistance.