|Measuring Speaker T-S Parameters
To properly determine the T-S parameters of your speaker, you will need:
Set up diagram
An Audio sine-wave generator.
A Frequency Counter (unless the dial on your audio generator is very accurate).
An AC voltmeter that will read accurately down in the millivolt range.
A 1000 ohm, 5% resistor.
A 10 ohm 1% resistor.
The test setup for measuring the speaker's impedance is shown here.
Make sure you connect everything as shown.
Calibrate the system by inserting the 10 ohm resistor in
place of the speaker.
Adjust the voltage output of the generator until the AC Voltmeter reads 0.01 volts.
Replace the 10 ohm resistor with the speaker to be tested.
Make sure you keep the output voltage constant throughout the tests.
.01 volts represents 10 ohms, 0.015 volts represents 15 ohms, etc.
Vary the frequency control of the generator to find maximum resistance
( Rmax ), which is indicated by the highest reading on the AC Voltmeter.
This is the free air resonant frequency of the speaker ( Fs ).
To determine the diameter of the speaker, take the size of the speaker (e.g. 12") times .85 and convert to cm by taking the result times 2.54
Impedance to Frequency Plot
resistance ( R x ) = ohms.
With the speaker facing upward, place small weights or U. S. nickels evenly around the dust
cap in the center. 6 nickels equal about 30 grams. With the added mass on the speaker, find the shifted
resonant frequency using the same method you used before to determine the free air resonant frequency.
The T-S Parameters For This Speaker
To find the voice coil inductance of the speaker, set the frequency of the generator to 1000Hz
and measure the resistance using the same method as before.