Audio Speakers Driver Parameters ~ Calculators

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.

Set up diagram

Setup diagram

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 ).

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

  Adjustfrequency  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-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.

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

  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.

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'sdamping abilities.
Qes =    The electrical gauge of the control on a driver coming fromthe 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 asthe suspension system of the driver.
EBP  =    The Efficiency Bandwidth Product.

   To find the voice coilinductance of the driver, set the frequency of the sine-wave generator at 1000 Hz andmeasure the resistance.

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