Parameters of a driver

   You will need an audio sine-wave generator, frequency counter, ac voltmeter, 1000 ohm resister, a 10 ohm 1 % precision resistor, and the driver to test.

   The test setup for measuring driver impedance is shown here.  Connect everything as shown.

Set up diagram

Setup diagram

   First, calibrate by inserting the 10 ohm resistor in place of the driver.

   Adjust the voltage output of the audio frequency sine-wave generator until the ac voltmeter reads 0.01 volts.  

   Replace the 10 ohm resistor with the driver to be tested.

   Keep the output voltage constant.   0.01 volts represents 10 ohms, 0.015 volts represents 15 ohms, etc.

   Vary the frequency control of the audio frequency generator to find maximum resistance ( Rmax ).  At that point, frequency is resonant frequency ( Fs ).

Enter diameter1 of speaker cone :   cm
Enter the maximum resistance ( Rmax )
at resonant frequency :
Enter the resonant frequency ( Fs ) :   Hz

  Adjust frequency  to 1 Hz  to find ( Re ).

Enter resistance at 1 Hz ( Re ) :   ohms

Impedance to frequency curve

Impedance to frequency curve

  resistance ( R x ) = ohms.

   Adjust the sine-wave generator until the resistance is equal to Rx.  This will occur twice as shown in the graph above.   F1 is the lower frequency when the resistance equals Rx.  F2 is the higher frequency when the resistance equals Rx.

Enter the lower frequency ( F 1 ) at R x : Hz
Enter the higher frequency ( F 2 ) at R x : Hz

  With the speaker facing upward place small weights or  U. S. nickels evenly around the dust cap in the center.   6  U. S. nickels equals 30 grams. With the mass on the speaker find the shifted resonant frequency.

Enter the mass : grams
Enter the shifted resonant frequency : Hz

Parameters of the driver

Symbol Value Definition
Qms =    The mechanical control coming from the suspension system's damping abilities.
Qes =    The electrical gauge of the control on a driver coming from the counter - EMF generated in the voice coil.
Qts =    The total Q of the driver.
Cms =    m / N The compliance of the driver.
Vas =    liters The equivalent volume of air having the same compliance as the suspension system of the driver.
EBP  =    The Efficiency Bandwidth Product.

   To find the voice coil inductance of the driver, set the frequency of the sine-wave generator at 1000 Hz and measure the resistance.

Enter resistance at 1000 Hz  : 
Inductance of voice coil  =  mH